Control of Beam Current in a Particle Accelerator

Abstract

An exemplary particle accelerator includes a particle source for providing particles to a magnetic cavity, a circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from an ionized plasma in an orbit within the magnetic cavity, where the RF voltage has a smaller gradient when the particles are injected into the magnetic cavity than when the particles are accelerated within the magnetic cavity, and an extraction channel for receiving particles from the magnetic cavity for output as a particle beam from the particle accelerator.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority of U.S. Provisional Application No. 63 / 392,264, filed on July 26, 2022. The content of U.S. Provisional Application No. 63 / 392,264 is incorporated herein by reference.

[0002] This specification describes examples of techniques for controlling beam current in a particle accelerator.

Background Art

[0003] A particle therapy system uses a particle accelerator to generate a particle beam for treating an irradiation target such as a tumor. An attribute of the particle beam is its beam current or beam intensity. The beam current is a function of the number of particles injected into the particle accelerator. The higher the beam current, the more capable it is of treating the irradiation target at a higher dose rate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Means for Solving the Problems

[0005] An exemplary particle accelerator includes a particle source for providing particles to a magnetic cavity, a circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from an ionized plasma in an orbit within the magnetic cavity, the RF voltage having a smaller slope when the particles are injected into the magnetic cavity than when the particles are accelerated within the magnetic cavity, and an extraction channel for receiving particles from the magnetic cavity for output as a particle beam from the particle accelerator. The particle accelerator can include one or more of the following features, either alone or in combination.

[0006] The RF voltage can have a first slope when the particles are injected into the magnetic cavity and a second slope when the particles are accelerated within the magnetic cavity. The first slope can be smaller than the second slope, at least during the RF voltage fall slope. The first slope can be at least 50% smaller than the second slope. The first slope can be at least 30% smaller than the second slope. The first slope can be at least 20% smaller than the second slope. The slope that becomes smaller when the particles are injected into the magnetic cavity can correspond to an increase in the current in the particle beam. The slope that becomes smaller when the particles are provided to the magnetic cavity can be proportional to an increase in the current in the particle beam.

[0007] The particle accelerator can include an RF controller that includes a rotary capacitor for varying the RF voltage. The rotary capacitor can include plates having a shape based on a targeted reduction of the RF voltage slope. The particle beam can be output at a FLASH dose, such as a dose exceeding 20 grays per second over a duration of less than 5 seconds.

[0008] An exemplary particle therapy system includes the aforementioned particle accelerator and a gantry configured to enable the output of a particle beam to a patient. The gantry can include a conduit for transporting the particle beam. The conduit can include a magnetic dipole configured to bend the particle beam at least 90° toward the patient. The magnetic dipole can be mounted for rotation around the gantry. The magnetic dipole can be configured to bend the particle beam at least 90° in the presence of a magnetic field of at least 3 Tesla (T).

[0009] An exemplary system includes a particle source for providing particles to a magnetic cavity, a circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate particles in an orbit within the magnetic cavity from an ionized plasma, a control system for controlling the particle source to provide particles to the magnetic cavity based on the slope of the RF voltage, and an extraction channel for receiving particles from the magnetic cavity for output as a particle beam from the particle accelerator. The exemplary system can include one or more of the following features, either alone or in combination.

[0010] The control system can be configured to control the particle source to provide particles to the magnetic cavity at or near the top of the waveform including the RF voltage. The system can include a comparator circuit for identifying a location at or near the top of the waveform representing the RF voltage. The control system can be configured to control the particle source to provide particles to the magnetic cavity between a first waveform generated for an injection cycle, which has an increased waveform width relative to a second waveform generated for an acceleration cycle, and the RF voltage having the first waveform. The control system can be configured to control the particle source to provide particles to the magnetic cavity at or near the top of the waveform generated for the injection cycle. The waveform generated for the injection cycle can have an increased waveform width relative to the waveform generated for the acceleration cycle.

[0011] The particle beam can be output at a FLASH dose. The particle beam can be output at a dose exceeding 20 grays per second over a duration of less than 5 seconds. The system can include a gantry configured to enable output of the particle beam to a patient. The gantry can include a conduit for transporting the particle beam. The conduit can include a magnetic dipole configured to bend the particle beam towards the patient by at least 90°. The magnetic dipole can be mounted for rotation around the gantry. The magnetic dipole can be configured to bend the particle beam by at least 90° in the presence of a magnetic field of at least 3 tesla (T).

[0012] An exemplary particle source includes a tube for introducing gas into a region where the particles are to be accelerated, the tube having an opening through which the particles are released into the region, an electrode at a different end of the tube for applying a potential to ionize the gas and thereby create particles, and a valve controllable to allow the gas to reach the opening or to prevent the gas from reaching the opening. The particle source can include one or more of the following features, either alone or in combination.

[0013] The valve can be within the tube and closer to the opening than either of the electrodes. The valve can include a piezoelectric displacement valve. The pressure of the gas within the tube can be 10 -4 Torr (0.0133322 Pascal (Pa)) or more. Ionizing the gas can create a plasma within the tube. The plasma can have at least a predefined particle density. The predefined particle density can be 10 15 ions / cm 3 or more. The valve can be located 3 centimeters (3 cm) or less from the opening. The valve can be located 2 centimeters (2 cm) or less from the opening. The valve can be located between 1 centimeter (1 cm) and 4 centimeters (cm) from the opening. The electrode can include a cathode, which is periodically charged to create an electrical pulse that ionizes the gas to create a plasma and releases particles into the region. The electrical pulse can be created at intervals of 1 millisecond or more over a duration on the order of single-digit microseconds. The tube can be completely separated within the region. The tube can include the opening within the region but not be completely separated within the region.

[0014] An exemplary system includes a particle source for providing particles to a magnetic cavity, a circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate the particles in an orbit within the magnetic cavity, and a control system for controlling the particle source to provide particles to the magnetic cavity. The particle source is a tube for introducing gas into the region of the magnetic cavity where the particles are to be accelerated, the tube having an opening through which the particles are emitted into the region, the tube, electrodes on different sides of the opening for applying a potential to ionize the gas and thereby create the particles, and a valve controllable to allow the gas to reach the opening or to prevent the gas from reaching the opening. The system can include one or more of the following features, either alone or in combination.

[0015] The gas in the tube can be under a first pressure and the magnetic cavity can be at a second pressure that is less than the first pressure. The valve can be controllable to reduce the effect of the first pressure in the tube on the second pressure in the magnetic cavity. The valve can be controllable to prevent the gas from reaching the opening during times when a potential is not applied to the electrodes.

[0016] The electrode can include a cathode, which is periodically charged, thereby creating an electrical pulse that ionizes a gas to create a plasma and releases particles into the region. The gas in the tube can be under a first pressure, and the magnetic cavity can be at a second pressure that is different from (e.g., less than) the first pressure. The valve can be controllable to prevent the gas from reaching the opening during at least a portion of the time when the electrical pulse is not being created. The valve can be controllable to allow the gas to reach the opening when a potential is applied to the electrode. The valve can be controllable to allow the gas to reach the opening only when a potential is applied to the electrode and only for a predetermined duration prior to the potential being applied to the electrode.

[0017] The electrode can include a cathode, which is periodically charged, thereby creating an electrical pulse that ionizes a gas to create a plasma and releases particles into the region. The gas in the tube can be under a first pressure, and the magnetic cavity can be at a second pressure that is less than the first pressure. The valve can be controllable to allow the gas to reach the opening during the time when the electrical pulse is being created. The valve can be controllable to allow the gas to reach the opening only during the time when the electrical pulse is being created and only for a predetermined duration prior to the electrical pulse being created. The valve can be within the tube and can be closer to the opening than either of the electrodes. The valve can include a piezoelectric displacement valve.

[0018] Any two or more of the features described in this specification (including this summary section) can be combined to form implementations not specifically described herein.

[0019] The control of the various systems or portions thereof described herein can be implemented via a computer program product that includes instructions, which are stored on one or more non-transitory machine-readable storage media, and which are executable on one or more processing devices (such as, for example, a microprocessor, an application specific integrated circuit, or programmed logic such as a field programmable gate array, etc.). The system or portion thereof described herein can be implemented as an apparatus, method, or medical system that includes one or more processing devices for implementing control of the described functions and a computer memory for storing executable instructions. The devices, systems, and / or components described herein can be configured, for example, through design, construction, placement, installation, programming, operation, activation, deactivation, and / or control.

[0020] Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

Brief Description of the Drawings

[0021]

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DETAILED DESCRIPTION OF THE INVENTION

[0022] Like reference numerals in different figures indicate like elements.

[0023] Described herein are exemplary particle therapy systems configured to generate beam currents and particle beam intensities usable in high-dose-rate (or FLASH) particle beam therapy, and particle accelerators for use therewith. Generally, the systems and accelerators described herein are controllable to increase the amount (e.g., number) of protons or ions (commonly referred to as "particles") injected into the particle accelerator in order to affect the beam current (e.g., to increase the beam current). In some implementations, the system is configured to vary the frequency of a radio frequency (RF) voltage provided to the particle accelerator to increase the time period during which particles are injected into and accepted by the accelerator. In some implementations, the system is configured to select a point on an RF waveform having the smallest or a relatively small slope and to inject particles into the accelerator at that time. The effect is an increase in the time period during which particles are injected into and accepted by the accelerator. The increase in the amount of particles accepted by the accelerator results in an increase in the beam current. In some implementations, the system is configured to adjust the pressure inside the particle accelerator to reduce the effect of collisional particle losses.

[0024] FIG. 1 shows a cross-section of the components of an exemplary superconducting synchrocyclotron 10 that can be used to provide a particle (e.g., proton) beam in a particle beam (e.g., proton beam) therapy system having one or more features of the type described in the preceding paragraphs. In this example, the components include superconducting magnets. The superconducting magnets include superconducting coils 13 and 14. The superconducting coils are formed from a plurality of integrated conductors, each of which includes superconducting strands (e.g., four strands or six strands) wound around a central strand that may itself be superconducting or non-superconducting. Each of the superconducting coils 13, 14 is for conducting a current that generates a magnetic field (B). Magnetic yokes 16, 17 or smaller pole pieces shape the magnetic field within a magnetic cavity (referred to herein as the "cavity") 19 where particles are accelerated. In one example, a cryostat (not shown) uses liquid helium (He) to conductively cool each coil to a cryogenic superconducting temperature (e.g., approximately 4 degrees Kelvin (K)).

[0025] As shown in FIG. 2, the two superconducting magnet coils 13, 14 are centered on a common axis and are spaced apart along the axis. The coils can be formed from Nb3Sn-based superconducting strands. The coils are mounted on a reverse stainless steel bobbin 20. The geometry of the coils is maintained by the reverse stainless steel 20, which exerts a restoring force against the distortion force (or hoop force) created when the coils are energized.

[0026] The superconducting coil is maintained at a temperature close to absolute zero (e.g., about 4°K) by surrounding the coil assembly (coil and bobbin) inside an evacuated annular aluminum or stainless steel cryostat chamber 21 that provides free space around the coil structure except for a limited set of support points. The coil assembly and the cryostat chamber are mounted within and completely surrounded by magnetic yokes 16 and 17, which can be considered collectively as a single magnetic yoke. The magnetic yokes provide a path for the return magnetic field flux, magnetically shield the volume between the yoke pole faces, and prevent external magnetic influences from disturbing the shape of the magnetic field within its cavity. Also, the yokes serve to reduce the stray magnetic field in the vicinity of the accelerator.

[0027] As shown in FIG. 3, the coil position is maintained relative to the magnetic yoke and the cryostat using a set of warm-to-cold support straps 22, 24, 26. Supporting the bobbin and the coil by the straps reduces the heat leakage imparted to the cryostat by a rigid support system. The straps are arranged to withstand the changing gravity acting on the coil. They withstand the combined effect of gravity and the large eccentric forces realized by the coil when the coil is displaced from a position completely symmetric with respect to the magnet yoke. Additionally, the straps act to reduce the dynamic forces imparted to the coil when the gantry accelerates and decelerates as the position of the gantry is changed.

[0028] In some implementations, such as the implementations shown in FIGS. 1 through 3, a magnetic shield (not shown) surrounds the yoke. The return yoke and the shield act together to reduce the stray magnetic field, thereby reducing the likelihood that the stray magnetic field will adversely affect the operation of the particle accelerator.

[0029] In some embodiments, the return yoke and / or shield can be replaced by, or enhanced by, an active return system. An exemplary active return system includes one or more active return coils that conduct current in a direction opposite to the direction of the current through the main superconducting coils 13, 14. In some embodiments, there is an active return coil for each superconducting main coil, for example, two active return coils, one for each main superconducting coil. Also, each active return coil can be a superconducting coil that concentrically surrounds the outside of the corresponding main superconducting coil. In some embodiments, the active return coil can be, or can include, a non-superconducting coil. By using an active return system, relatively large ferromagnetic magnetic yokes 16, 17 can be replaced with smaller and lighter pole pieces. Thus, the size and weight of the synchrocyclotron can be further reduced without sacrificing performance. An example of an active return system that can be used is described in Patent Document 1 (Zwart) entitled "Active Return System". The content of Patent Document 1, particularly the content related to the return coil configuration (for example, FIGS. 2, 4, and 5 of Patent Document 1, and the accompanying description), is incorporated herein by reference.

[0030] Another component of the accelerator is the source of the particles to be accelerated (referred to as the particle source). For electron accelerators, various cathode technologies, such as thermionic emitters, field emitters, and photocathodes, readily provide a sufficient number of electrons for the beam. Also, these electron sources add a minimal gas load to the accelerator vacuum system. However, proton and other ion accelerators may use more complex particle sources because ions cannot be easily removed from bulk metal as electrons can. The particle source can take many forms, including sputtering sources and laser-driven sources. One class of particle sources is the plasma-based particle source. This class of particle source involves the addition of a source gas containing the atoms / molecules to be ionized. The resulting particles are extracted from the plasma and injected into the accelerator.

[0031] Exemplary plasma-based particle sources include the particle source 25 of FIGS. 1, 3, and 4. The particle source 25 is, in this example, a Penning Ion Gauge (PIG) source and is configured to provide a column of plasma that is at least partially ionized within the cavity 19. Referring to FIGS. 1 and 3, the particle source 25 is near the magnetic center of the synchrocyclotron and is arranged such that the particles are present at the synchrocyclotron midplane where, as described below, the particles can be acted upon by an RF voltage field.

[0032] As described above, the particle source can have a PIG geometry. In the PIG geometry, two high voltage electrodes, such as cathodes 33a, 33b (Fig. 4), are arranged at different or opposite ends of the particle source such that they are linearly aligned. For example, one cathode 33a can be on one side of the acceleration region 38 and the other cathode 33b can be on the other side of the acceleration region 38 and can be aligned with the magnetic field lines in the cavity 19. A gas tube 36 (which may be referred to as a "chimney") extends from each end of the particle source towards the acceleration region. In an implementation where the particle source is not interrupted (see, for example, Fig. 15 described below), the tube extends through the acceleration region. The particle source 25 includes an emitter side 31 that includes a gas feed portion 32 for receiving gas and a reflector side 34. The gas is introduced through the gas feed portion 32 and propagates in the direction of arrow 29 in and through the tube 36, and the tube 36 holds the gas. When a relatively small amount of gas (e.g., hydrogen / H2, etc.) occupies the region in the tube between the cathodes, a plasma column can be formed from the gas by applying a voltage to the cathodes. The applied voltage causes electrons to flow along the magnetic field lines (essentially parallel to the tube wall) and ionize the gas molecules concentrated inside the tube. The background magnetic field prevents the scattering of the ionized gas particles and generates a plasma column between the cathodes.

[0033] The gas in the gas tube can include a mixture of hydrogen and one or more other gases. For example, the mixture can contain hydrogen and one or more of the noble gases such as helium, neon, argon, krypton, xenon, and / or radon (although the mixture is not limited to use with noble gases). In some implementations, the mixture can be a mixture of hydrogen and helium. For example, the mixture can contain at least about 75% hydrogen and at most about 25% helium (with possible trace gases included). In another example, the mixture can contain at least about 90% hydrogen and at most about 10% helium (with possible trace gases included). By way of example, the hydrogen / helium mixture can be any of >95% / <5%, >90% / <10%, >85% / <15%, >80% / <20%, and >75% / <20%.

[0034] As described above, an example of a particle source 25 having a PIG geometry that can be used in the synchrocyclotron 10 is shown in FIG. 4. Also, an exemplary implementation of the particle source 25 is described in Patent Document 2. The content of Patent Document 1, particularly the content related to the interrupted particle source (e.g., FIGS. 3A, 3B, and 4 to 7 of Patent Document 2, and the accompanying description), is incorporated herein by reference.

[0035] The particle source is capable of passing through a dummy dee (not shown in FIG. 4) and adjacent to the active (RF) dee 37, and they are described below. During operation, the particle source periodically emits pulses and provides particles (e.g., protons) to the cavity 19. The magnetic field between the active dee and the dummy dee causes the particles to be accelerated outward. The acceleration is spiral so as to generate an orbit around the plasma column, and the particle-to-plasma-column radius is gradually increasing. The radius of curvature of the spiral depends on the mass of the particle, the energy imparted to the particle by the RF field, and the strength of the magnetic field. When the magnetic field is high, it may be difficult to impart sufficient energy to the particle so that it has a large enough radius of curvature to clear the physical housing of the particle source during its initial turn during acceleration.

[0036] The magnetic field is relatively high in the central region of the cavity 19 containing the particle source, for example, on the order of 2 tesla (T) or more (e.g., 2.5T, 3T, 4T, 5T, 6T, 8T, 8.8T, 8.9T, 9T, 10.5T, or more). As a result of this relatively high magnetic field, the initial particle-to-ion-source radius is relatively low for low-energy particles, where low-energy particles include those first extracted from the plasma column. For example, such a radius can be on the order of 1 millimeter (mm). Since the radius is very small, at least initially, some particles can contact the housing of the particle source, thereby preventing further outward acceleration of such particles. Thus, the housing of the particle source 25 can be interrupted (e.g., separated) to form two parts. That is, a portion of the housing of the particle source can be partially or completely removed in the acceleration region 38, thereby creating an opening 38a around the area where the particles are output from the particle source. Also, the housing can be removed for distances above and below the acceleration region. For example, the housing can be removed for distances in the single-digit millimeters or single-digit centimeters above and below the acceleration region.

[0037] Differently described, the opposing parts of the particle source 25 aligned with the beam's axis of rotation are separated so that the tip of the particle source does not reach the acceleration region 38. This design results in a relatively high conductance between the plasma and the cavity (vacuum space). In one example, the particle source ideally has 10 15 ions / cm 3 or 10 15 electrons / cm 3Create a plasma having a density of (cubic centimeters) or greater. If the pressure in the particle source is too low, the plasma density will be too low and the overall beam current will be limited by the number of protons that can be extracted from the plasma. The pressure here refers to the pressure of the gas in the particle source. If the pressure in the particle source is too high, the pressure from the particle source will increase the pressure in cavity 19 and may adversely affect particle acceleration as described below. Also, when the pressure in the particle source is too high, although there are protons available for extraction from the plasma, the overall beam current of the accelerator is limited by the collision losses of these protons due to the background gas from the particle source. This can result in degraded performance for both the particle accelerator and the particle source.

[0038] In this regard, in some examples, plasma-based particle sources such as particle source 25 can operate at a pressure of 10 -4 Torr (0.0133322 pascals (Pa)) or above. In some implementations, particle acceleration and beam transport in cavity 19 work better or optimally at a negative pressure approaching vacuum (e.g., a negative pressure of 10 -5 Torr (0.0013332 pascals) or less). When the pressure in cavity 19 increases above vacuum, the scattering of low-energy particles in the particle beam line also increases. For devices such as synchrocyclotrons where particles are injected into the cavity at low energy and accelerated in the same cavity, the high pressure required for the plasma-based particle source can limit the beam current that the synchrocyclotron can produce due to such scattering losses in the beam line.

[0039] Thus, the pressure in the particle source (e.g., particle source 25), which is greater than the pressure in the cavity 19, can increase the pressure in the cavity 19 and lead to limitations in the magnitude of the beam current and other undesirable effects (including those described above). To address these issues, the particle source 25 is configured to limit the exposure of the cavity to the pressure in the particle source and is controllable in that regard. For this purpose, the particle source 25 includes a valve 120 (e.g., a high-speed pulsed gas valve, etc.) that adjusts the gas flow through the particle source. The valve is controllable to reduce the amount of gas provided to the cavity by reducing the duration for which the particle source opening to the cavity is exposed to the gas. Reducing the exposure of the cavity to the gas from the particle source reduces the exposure of the cavity to the pressure in the particle source. As a result, the likelihood that the pressure in the cavity will increase as a result of the exposure to the particle source pressure is also reduced. In one example, the valve is controllable to prevent gas from reaching the particle source opening 38a during the time when no cathode electrical pulse (e.g., potential) is being generated and to allow gas to reach the opening 38a when an electrical pulse is generated and applied to the cathode. Also, the valve is controllable to allow gas to reach the opening 38a for a predefined duration before an electrical pulse is generated and applied to the cathode. In some cases, the valve is controllable to allow gas to reach the opening 38a only during the time when an electrical pulse is generated and applied to the cathode and only for a predetermined duration before the electrical pulse is generated. In these examples, at all other times, gas does not reach the opening 38a.

[0040] As shown, valve 120 is included within tube 36 that provides gas to opening 38a in the acceleration region. In this example, valve 120 is positioned within the path of the gas flow towards opening 38a and is positioned on one side of the opening. When closed, the valve creates a gas-tight seal within tube 36 and prevents the flow of gas through the valve. When open, the valve allows gas to flow through the valve and through the entire length of the tubing (including the separation region) between the two cathodes.

[0041] In one example, a piezoelectric actuator controls valve 120. When an ion pulse is requested by the control system, the valve opens, allowing gas flow into tube 36 to create a plasma column with a targeted high plasma density. This allows for the extraction of a large number of protons per bunch moving through the cavity. In some examples, since the valve is open only over the duration of particle injection, the amount of gas provided to the cavity by the particle source (referred to as the "gas load") can be reduced compared to a source that allows gas to continuously flow into the particle source until the accelerator is ready to create a beam. This reduces the pressure provided to the cavity by the particle source. In some examples, the particle source is effectively active for less than 2% of the time the accelerator is operating to create a particle beam. This can result in a reduction of more than one order of magnitude in the pressure within the cavity compared to an accelerator where the particle source is always active and constantly provides gas and pressure to the cavity.

[0042] The valve 120 is a piezoelectric displacement valve in this example. However, other types of piezoelectrically actuated valves or electromechanical valves can also be used. FIG. 14 shows an example of a piezoelectric displacement valve 120a that can be used as the valve 120 in a particle source such as the particle source 25. In this example, the valve 120a is connected to a tube 36a, and the tube 36a can have the structure and function of the tube 36 in FIG. 4. The gas flows through the tube 36a in the direction of arrow 122 into the particle source towards the particle source opening. When closed, the valve 120a creates a gas-tight seal in the tube 36a, and when open, the valve 120a allows the gas to flow through the valve into and towards the acceleration region and the particle source opening (such as the opening 38a in FIG. 4). The valve 120a includes a housing 124 that includes a region 125, and when the valve 120a is open, the gas passes through the region 125. The valve 120a includes a piezoelectric actuator 126 that receives one or more electrical signals through wires 127a, 127b. In response to these electrical signals, the piezoelectric actuator 126 contracts, for example, in the directions of arrows 128, 128a. The valve 120a also includes a toroidal seal 129, and the toroidal seal 129 is physically connected to the piezoelectric actuator 126 and a coaxial seal 130 within the toroidal seal. The valve 120a includes a region 132 and a stationary wire 133. The gas passes from the region 125 through the region 132 and exits the valve 120a, and the stationary wire 133 can also receive an electrical signal that affects the operation of the piezoelectric actuator 126.

[0043] Referring back to FIG. 4, the valve 120 can be positioned closer to the opening 38a than either of the cathodes 33a and 33b. By positioning the valve 120 closer to the opening than either of the cathodes, the time it takes for gas to reach the opening 38a during operation of the particle source (i.e., when the valve is open) can be reduced, enabling the particle source to produce pulses at a higher rate. That is, the gas does not have to travel as far to reach the opening, enabling operation of the particle source at a higher rate. In one example, the valve 120 is located 3 centimeters (3 cm) or less from the opening 38a. In one example, the valve 120 is located 2 centimeters (2 cm) or less from the opening 38a. In one example, the valve 120 is located between 1 centimeter (1 cm) and 4 centimeters (cm) from the opening 38a. Generally, the valve 120 can be located at any suitable distance from the opening 38a. The location of the valve can be (partially) based on its size. That is, the valve should be small enough to fit close to the opening without blocking it.

[0044] In the exemplary valve of FIG. 14, a control system controls a circuit (not shown) to periodically provide electrical signals to wires 127a, 127b. The electrical signals coincide with the times at which pulses will be provided by the particle source. For example, the cathode can be periodically charged, thereby creating an electrical pulse that ionizes the gas, pulses the plasma, and releases particles into cavity 19. The electrical pulses applied to the cathode can be created every millisecond or more over a duration on the order of single-digit microseconds (from 1 μs to 9 μs, these numbers being merely examples). The electrical signal provided to piezoelectric actuator 126 can precede these electrical pulses by a predetermined amount of time (which can also be measured in single-digit microseconds), ensuring that gas is present at the opening of the particle source when the electrical pulse is applied to the cathode. Also, the electrical signal provided to piezoelectric actuator 126 extends throughout the duration of the electrical pulse applied to the cathode, ensuring that gas remains at the opening of the particle source for the entire time the electrical pulse is applied to the cathode. In other words, the electrical signal is provided to piezoelectric actuator 126 immediately before the electrical pulse is applied to the cathode to open valve 120, such that there is time for gas to pass through the valve and fill the entire tube (including opening 38a) before the cathode is pulsed. The valve is controlled to remain open for the entire duration that the cathode is pulsed, ensuring that gas remains to create an ionized plasma column in the particle source. When the potential is removed from the cathode or immediately thereafter, valve 120a is closed by stopping the electrical signals to wires 127a and 127b.

[0045] In this regard, when an electrical signal is applied to wires 127a and 127b, the piezoelectric actuator 126 contracts in the directions of arrows 128 and 128a. Also, this contraction causes the torlon seal 129 and the coaxial seal 130 to move in the direction of arrow 128a. The reason is that they are physically connected to the piezoelectric actuator 126 and move together with it. These movements of the various valve components create a path for the gas to travel from region 125, through the gap created at location 135 when the piezoelectric actuator contracts, through region 132, out of the valve 120a from there, and into the remainder of the particle supply tube (including the region containing the opening 38a). Since the actuator 126 is piezoelectrically activated, the actuator 126 can operate at a speed on the order of single-digit microseconds, although in some implementations the operation may be slower than that. Thus, the valve 120a can open and close on the order of single-digit microseconds, although in some implementations the operation may be slower than that. To close the valve 120a, the electrical signal is removed from wires 127a and 127b, which causes the piezoelectric actuator 126 to expand in the direction of arrow 129. This expansion closes the gap 135, thereby preventing the flow of gas out of the valve.

[0046] Thus, the valve 120 / 120a can be controlled to reduce the duration during which the cavity 19 is exposed to the pressure in the tube / particle source, thereby reducing the effect of the pressure in the tube / particle source on the pressure in the cavity. As described, the valve 120 / 120a can be controlled to prevent gas from reaching the opening during the time when the electrical pulse (potential) is not applied to the electrodes, and as a result, the pressure from the tube / particle source does not reach the opening during that time and does not affect the pressure in the cavity (e.g., increase the pressure).

[0047] FIG. 15 shows another example of a particle source 140 that can be used in the particle accelerator described herein, which can include a valve (e.g., valve 120b, etc.) to control the flow of gas 142 in the tube (or chimney) 143 of the particle source. The particle source 140 includes cathodes 144a and 144b at opposite ends or different ends or portions thereof, which are electrically pulsed to create a partially ionized plasma from the gas, and the particle source 140 includes a slit 146, which is an opening of a certain type through which a pulse of charged particles is emitted into a magnetic space such as cavity 19. The anode 147 is at ground potential. The gas is introduced into the particle source through an inlet 148 and travels in the direction of arrow 150 up to the valve 120b when the valve 120b is closed and through the valve 120b when the valve 120b is open.

[0048] Valve 120b is an exemplary implementation of valve 120 of FIG. 4 and can have the structure and function of valve 120 and valve 120a of FIG. 14. Valve 120b is arranged and controllable as described herein to control when gas 142 is allowed to reach slit 146. For example, as described above, valve 120b can be controlled to prevent gas from reaching slit 146 during the time when no cathode electrical pulse (e.g., potential) is being generated, and can be controlled to allow gas to reach slit 146 when an electrical pulse is generated and applied to the cathode. Also, the valve can be controlled to allow gas to reach slit 146 for a predefined duration before an electrical pulse is generated and applied to the cathode. In some cases, the valve can be controlled to allow gas to reach slit 146 only during the time when an electrical pulse is generated and applied to the cathode and only for a predetermined duration before the electrical pulse is generated. As described above, the particle source can thus output a pulse of particles into the cavity while reducing, minimizing, or substantially eliminating the influence of the pressure in the particle source on the pressure in the cavity.

[0049] The cavity 19 in which acceleration occurs surrounds the RF deep plate, the dummy deep plate, and the particle source and is evacuated by a vacuum pump. Maintaining a high vacuum / very low pressure ensures that the accelerating particles are not lost due to collisions with gas molecules and allows the RF voltage to be maintained at a higher level without arcing to ground. The voltage source provides an RF voltage to the cavity 19 and accelerates pulsed particles from the plasma column created by the particle source. As described, in one example, the particle accelerator is a synchrocyclotron. Thus, the RF voltage is swept over a wide range of frequencies to account for relativistic effects (such as increasing particle mass, etc.) on the particles when accelerating them within the cavity 19. The RF voltage drives the active deep plate (described below) contained within the cavity and has a frequency that is swept downward during the acceleration cycle to account for the increasing relativistic mass of the protons and the decreasing magnetic field. The dummy deep plate acts as a ground reference for the deep plate. The magnetic field created by passing a current through a superconducting coil, together with the sweeping RF voltage, causes the particles from the plasma column to be orbitally accelerated within the cavity and the energy to increase as the number of turns increases. The particles in the outermost orbit are directed towards the extraction channel described below and are output from the synchrocyclotron as a particle beam. In a synchrocyclotron, the particle beam is pulsed and bunches of particles are output periodically.

[0050] In the examples of FIGS. 5 and 13, the active deep plate 40 (1000 in FIG. 13) is a hollow metal structure having two semi-circular surfaces 41, 42 surrounding the space 43, and protons are accelerated within the space 43 during its rotation. A duct 44 opening into the space 43 extends through the yoke to an external location, and a vacuum pump (not shown) can be attached from the external location to evacuate the space 43 and the remaining part of the space within the cavity 19 where acceleration takes place. In this example, the dummy die 45 includes a rectangular metal ring spaced near the exposed rim of the deep plate 40. The dummy die is grounded to the vacuum chamber and the magnet yoke. The deep plate 40 is driven by an RF signal applied at the end of a radio frequency transmission line to apply an electric field within the space 43. The RF signal has a frequency that decreases with time during the particle acceleration cycle as the accelerated particle beam increases in distance from the geometric center of the cavity.

[0051] The RF voltage can be tuned to maintain a high Q factor of the cavity during the frequency sweep, for example, by using a rotating capacitor / variable reactive element having meshing rotating and stationary blades. During each meshing of the blades caused by rotation, the capacitance increases, thus decreasing the resonant frequency of the cavity. The blades can be shaped to produce the required precise frequency sweep. The drive motor for the rotating capacitor can be phase-locked to the RF generator for precise control. In this example, during each meshing of the blades of the rotating capacitor, one bunch of particles is accelerated.

[0052] FIG. 13 shows an exemplary capacitive structure 1308 (including a capacitive circuit) for controlling the shape of an RF voltage waveform applied to a deep plate 1000 (such as die 40) over an RF frequency range. The dummy die is not shown in FIG. 13. For example, the capacitive structure 1308 can be configured and controlled to generate the RF waveforms shown in FIGS. 8, 9, and 10, as well as variations and / or combinations thereof. The semi-circular surfaces 1003, 1005 of the deep plate 1000, which define the boundaries of the region 1007 of the cavity 19 where particles are accelerated, are connected to the inner conductor 1300 and are housed within the outer conductor 1302. A high voltage is applied to the deep plate 1000 from a voltage source 1320 (e.g., an oscillating voltage input) through a power coupling device 1304 that electrically couples the voltage source to the inner conductor. In some implementations, the coupling device 1304 is positioned on top of the inner conductor 1300 and provides power transfer from the voltage source to the deep plate 1000. Additionally, the deep plate 1000 is connected to variable reactive elements 1306, 1308 to implement an RF frequency sweep and to vary the RF frequency range and waveform shape in response to commands from a control system. For example, the variable reactive element 1306 can be configured and controlled to vary the waveform widths 100, 102, 106 of FIGS. 8, 9, and 10, respectively. The variable reactive element 1308 can be configured and controlled to vary the maximum and minimum voltages of the RF voltage, for example, from those shown in FIGS. 8 and 9 to those shown in FIG. 10.

[0053] The variable reactive element 1306 can include one or more rotary capacitors having a plurality of blades 1310 rotatable using a motor (not shown) controlled by a control system. By engaging or disengaging the blades 1310 during each cycle of the RF sweep, the capacitance of the RF structure changes, and it changes the resonant frequency (RF) of the cavity 19 and the frequency of the voltage applied to the cavity 19. In some implementations, during each quarter cycle of the motor, the blades 1310 engage with each other. The capacitance of the RF structure increases and the resonant frequency decreases. When the blades 1310 disengage, the process is reversed. As a result, the power required to generate the high voltage required to be applied to the deep rate 1003 and accelerate the beam can be reduced to a fraction. In some implementations, the shape of the blades 1310 is machined to implement the dependence of the resonant frequency on time.

[0054] Blade rotation can be synchronized with RF frequency generation. By changing the Q factor of the cavity 19, the resonant frequency of the RF structure can be maintained near the frequency of the alternating voltage potential applied to the deep rate 1003.

[0055] The variable reactive element 1308 can be or can include a capacitor formed by the plate 1312 and the surface 1316 of the inner conductor 1300. The plate 1312 is movable along the direction 1314 towards or away from the surface 1316. The capacitance of the capacitor changes as the distance D between the plate 1312 and the surface 1316 changes. For each different frequency range that will be swept within the cavity 19 (e.g., to change the minimum frequency and / or the maximum frequency), the distance D is set to a specific value. To change the frequency range that will be swept within the cavity 19, the plate 1312 can be moved in response to the desired change in the frequency range. The control system can control the movement of the plate 1312 using a motor (not shown).

[0056] In some implementations, the inner and outer conductors 1300, 1302 include a metallic material such as copper, aluminum, or silver. Also, the blades 1310 and the plate 1312 can include the same or a different metallic material as the conductors 1300, 1302. The connection device 1304 can be an electrical conductor. The variable reactive elements 1306, 1308 can have other forms and can be connected to the deep plate 1000 in other ways to implement RF frequency sweeping and frequency range variation. In some implementations, a single variable reactive element can be configured to perform the functions of both of the variable reactive elements 1306, 1308. In some implementations, three or more variable reactive elements can be used.

[0057] FIG. 8 shows an exemplary change over time of an RF voltage frequency between a minimum frequency 50 and a maximum frequency 51, and examples of the minimum frequency 50 and the maximum frequency 51 are 90 megahertz (MHz) and 135 MHz, respectively. In a typical synchrocyclotron, the RF voltage waveform 55 remains the same when particles are injected into the cavity and when those particles are accelerated within the cavity. That is, the RF voltage waveform remains consistent during the acceleration cycle and the injection cycle, respectively. The acceleration cycle includes when particles are accelerated within the cavity, and the injection cycle includes when particles are injected from a particle source into the cavity, including, for example, when the particle source is pulsed. Consistency can be defined in terms of the pulse width 100, the pulse height 101, or a combination thereof.

[0058] The particle source 25 is controllable to provide particles at a specific frequency that is close to a decrease from a maximum RF frequency 51 to a minimum RF frequency 50 during a voltage frequency sweep. For example, as shown in FIG. 8, the particle source can be controlled to inject a pulse 56 composed of particles at any point between a start frequency 57 and an end frequency 58. The start maximum frequency (which is 125 MHz in this example) and the end minimum frequency (which is 124 MHz in this example) correspond to a predetermined frequency range, over which the particles have the greatest likelihood of being accepted into the synchrocyclotron. This frequency range is collectively referred to herein as the acceptance frequency. At the acceptance frequency, pulsed particles from the particle source have a high likelihood of acceleration given the magnetic and electric fields within the synchrocyclotron. The acceptance includes a cavity that receives the particles and an RF voltage that accelerates the particles within the cavity. Particles injected outside the acceptance frequency have a lower or lower likelihood of acceptance given the magnetic and electric fields within the synchrocyclotron. Thus, particle injection between the acceptance frequencies is targeted at creating a larger beam current. That is, the more particles that are accepted, the greater the density of particles in the resulting beam. A pulse of particles having a width over the entire acceptance frequency is shown in FIG. 8. Other exemplary pulses may not extend over the entire acceptance frequency.

[0059] The current extracted from the particle accelerator is based on the amount of particles injected into (and accepted by) the cavity. In some examples, particles can be successfully injected into the cavity only within a few percent of the acceptance frequency. Thus, the time during which particles can be injected into the cavity, and hence the total beam current of the accelerator, is limited by the slope of the frequency variation as a function of the time between particle source pulses. For example, for a synchrocyclotron with a 1% frequency acceptance, an injection frequency of 124 - 125 MHz, and an RF voltage frequency modulation (FM) rate of 0.075 MHz / microsecond (μs), a particle source pulse 56 with a width of 17 μs can be successfully injected into the synchrocyclotron. The duration of this pulse and the pulse repetition rate control the beam current that the synchrocyclotron can produce.

[0060] Thus, in some implementations, the RF voltage during the injection cycle (i.e., when particles are injected into the cavity) can be varied such that its slope is less than the average slope of the RF voltage waveform during the acceleration cycle. In one example, the slope of the RF voltage waveform during the injection cycle can be less than the slope of the RF waveform at the same point along the waveform during the acceleration cycle. A slope that is 25% less at particle source injection compared to the average slope during the acceleration cycle can produce 25% more beam current. In other words, a slope that is one-quarter as small extends the duration of the acceptance frequency, which allows four times as many particles to be injected during the extended acceptance frequency and results in four times as much beam current. This lower frequency modulation slope is implemented by a control system that controls the rate of rotation of the rotating capacitor 1306 (FIG. 13) and can provide a desired frequency profile as a function of time. Also, the shape of the leaf can be configured to affect the frequency.

[0061] In the exemplary operation of the particle accelerator of FIG. 1, the RF voltage waveform 55 of FIG. 8 is the RF voltage provided to cavity 19 during the acceleration cycle. The RF voltage waveform 60 of FIG. 9 is the RF voltage provided to cavity 19 during the injection cycle. As shown, the width 102 of waveform 60 is increased relative to the width 100 of waveform 55. For example, the width of waveform 60 can be twice, three times, four times, etc. the width of waveform 55. As a result, the slope 61 of waveform 60 at the acceptance frequencies 124 - 125 MHz during particle injection 62 is less than the slope 64 of waveform 55 (FIG. 8) at the acceptance frequencies 124 - 125 MHz during particle injection 65. As a result, the amount of particles that can be injected, as represented by pulse 69 (FIG. 9), is greater during the RF frequency sweep of FIG. 9 than when it is during the RF frequency sweep of FIG. 8 (represented by pulse 56 in FIG. 8). That is, in both examples, particles are injected between 125 MHz and 124 MHz. However, the time period between 125 MHz and 124 MHz is greater in waveform 60 than in waveform 55, so more particles can be injected using waveform 60. As a result, the beam current is increased by using waveform 60 during the injection cycle. Waveform 55 can continue to be used during the acceleration cycle. The rotating capacitors 1306 / 1310 described herein can be controlled to switch between waveform 55 and waveform 60 at an appropriate time, for example, based on the pulse timing of the particle source. For example, when a potential is applied to the particle source cathode, the rotating capacitor described herein can be controlled to switch from waveform 55 to waveform 60.

[0062] In some implementations, the reduction of the slope from RF voltage waveform 55 to RF voltage waveform 60 is proportional to an increase in current in the particle beam. In some implementations, the slope of the RF voltage waveform during the injection cycle is at least 75% less than the slope of the RF voltage waveform during the acceleration cycle. In some implementations, the slope of the RF voltage waveform during the injection cycle is at least 50% less than the slope of the RF voltage waveform during the acceleration cycle. In some implementations, the slope of the RF voltage waveform during the injection cycle is at least 30% less than the slope of the RF voltage waveform during the acceleration cycle. In some implementations, the slope of the RF voltage waveform during the injection cycle is at least 25% less than the slope of the RF voltage waveform during the acceleration cycle. In some implementations, the slope of the RF voltage waveform during the injection cycle is at least 20% less than the slope of the RF voltage waveform during the acceleration cycle. Generally, the slope of the RF voltage waveform during the injection cycle can be less than the slope of the RF voltage waveform during the acceleration cycle by any suitable percentage.

[0063] In some implementations, a particle source timing trigger generated using one or more frequency comparators can be used. By using one or more frequency comparators (which can use a minimum frequency slope for reliable operation) and a timing delay, the particle source trigger can be initiated at any point in the RF voltage waveform (including the top or near the top of the waveform where the slope is lower than at other points along the waveform). For example, referring to FIG. 10, by controlling the operation and / or shape of a capacitor (e.g., 1308), the RF voltage waveform can be generated such that the start of the acceptance frequency (e.g., 125 MHz) is at or near the top 70 of the RF waveform 71 (where the slope is less than at other parts of the waveform). For example, the acceptance frequency can start at the top of the waveform, or at 5% from the top on the falling slope, at 10% from the top on the falling slope, or at any suitable percentage from the top on the falling slope. In the implementation of FIG. 10, the amount of particles that can be extracted, as represented by the pulse 72, is greater than at other locations in the waveform where the slope 74 is greater. As a result, the beam current is increased. In some implementations, the waveform 71 can be used during the injection cycle, and the waveform 55 of FIG. 8 can be used during the acceleration cycle. In some implementations, the waveform 71 can be used during both the injection cycle and the acceleration cycle. In some implementations, the width 106 of the waveform 71 can be increased (relative to the waveform used during the acceleration cycle) like the width of the waveform 60, further increasing the duration of the acceptance frequency and the amount of particles that can be injected at that time.

[0064] FIG. 11 shows an example of an exemplary comparator circuit 75, which can be used to identify the start or end of an acceptance frequency, or to identify a location at or near the top of a voltage waveform. To implement this function, other types of frequency comparators can be used. In this example, individual RF voltage values (e.g., from waveform 71 of FIG. 10) can be sampled and digitized to create a first pulse train having a frequency F1, which can be compared to a reference pulse train having a frequency F2. F2 can be a reference frequency close to the maximum frequency of the RF waveform. The two pulse trains are provided to D flip-flops 76 and 77. The outputs of flip-flops 76 and 77, signals Q1 and Q2 respectively, are applied to a NAND gate 78. The output of NAND gate 78 controls whether to reset flip-flops 76 and 77. Signals Q1 and Q2 are provided to a low-pass filter 79 including a capacitor and two resistors, and the resulting filtered values are compared using an analog comparator 80. The output of frequency comparator 75 can determine a predefined point (e.g., at or near the top, etc.) along the RF voltage waveform based on the comparison performed using signals Q1 and Q2. That is, the frequency at which Q1 exceeds Q2 corresponds to a location at or near the top of the RF voltage waveform.

[0065] Referring back to FIG. 1, the magnetic field in cavity 19 is shaped to cause particles to move orbitally within the cavity as described above. An exemplary synchrocyclotron uses a magnetic field that is uniform in the angle of rotation and decreases in intensity with increasing radius. In some implementations, the maximum magnetic field created by the superconducting (main) coil can be in the range of 2.5 T to 20 T at the center of the cavity, which decreases with increasing radius. For example, the superconducting coil can be used to generate a magnetic field at one or more (or exceeding) the following magnitudes: 2.5 T, 3.0 T, 3.1 T, 3.2 T, 3.3 T, 3.4 T, 3.5 T, 3.6 T, 3.7 T, 3.8 T, 3.9 T, 4.0 T, 4.1 T, 4.2 T, 4.3 T, 4.4 T, 4.5 T, 4.6 T, 4.7 T, 4.8 T, 4.9 T, 5.0 T, 5.1 T, 5.2 T, 5.3 T, 5.4 T, 5.5 T, 5.6 T, 5.7 T, 5.8 T, 5.9 T, 6.0 T, 6.1 T, 6.2 T, 6.3 T, 6.4 T, 6.5 T, 6.6 T, 6.7 T, 6.8 T, 6.9 T, 7.0 T, 7.1 T, 7.2 T, 7.3 T, 7.4 T, 7.5 T, 7.6 T, 7.7 T, 7.8 T, 7.9 T, 8.0 T, 8.1 T, 8.2 T, 8.3 T, 8.4 T, 8.5 T, 8.6 T, 8.7 T, 8.8 T, 8.9 T, 9.0 T, 9.1 T, 9.2 T, 9.3 T, 9.4 T, 9.5 T, 9.6 T, 9.7 T, 9.8 T, 9.9 T, 10.0 T, 10.1 T, 10.2 T, 10.3 T, 10.4 T, 10.5 T, 10.6 T, 10.7 T, 10.8 T, 10.9 T, 11.0 T, 11.1 T, 11.2 T, 11.3 T, 11.4 T, 11.5 T, 11.6 T, 11.7 T, 11.8 T, 11.9 T, 12.0 T, 12.1 T, 12.2 T, 12.3 T, 12.4 T, 12.5 T, 12.6 T, 12.7 T, 12.8 T, 12.9 T, 13.0 T, 13.1 T, 13.2 T, 13.3 T, 13.4 T, 13.5 T, 13.6 T, 13.7 T, 13.8 T, 13.9 T, 14.0 T, 14.1 T, 14.2 T, 14.3 T, 14.4 T, 14.5 T, 14.6 T, 14.7 T, 14.8 T, 14.9 T, 15.0 T, 15.1 T, 15.2 T, 15.3 T, 15.4 T, 15.5 T, 15.6T, 15.7T, 15.8T, 15.9T, 16.0T, 16.1T, 16.2T, 16.3T, 16.4T, 16.5T, 16.6T, 16.7T, 16.8T, 16.9T, 17.0T, 17.1T, 17.2T, 17.3T, 17.4T, 17.5T, 17.6T, 17.7T, 17.8T, 17.9T, 18.0T, 18.1T, 18.2T, 18.3T, 18.4T, 18.5T, 18.6T, 18.7T, 18.8T, 18.9T, 19.0T, 19.1T, 19.2T, 19.3T, 19.4T, 19.5T, 19.6T, 19.7T, 19.8T, 19.9T, 20.0T, 20.1T, 20.2T, 20.3T, 20.4T, 20.5T, 20.6T, 20.7T, 20.8T, 20.9T, or more. Moreover, the superconducting coil can be used when generating a magnetic field outside the range of 2.5T to 20T, or a magnetic field within the range of 3T to 20T that is not specifically listed herein.

[0066] By generating a high magnetic field having a magnitude such as those described above, it is possible to reduce the bending radius of the particles orbiting in cavity 19. As a result of the reduction in the bending radius, it is possible to create a greater number of particle orbits within a given sized cavity. Therefore, a greater number of orbits can be fitted into a smaller cavity. Reducing the size of the cavity generally reduces the size of the particle accelerator. The reason is that a smaller cavity requires a smaller magnetic yoke or pole piece among other components. In some implementations, the size or volume of the particle accelerator can be 4m 3 (cubic meters) or less, 3m 3 or less, or 2m 3 or less.

[0067] Particles traverse generally spiral orbital paths that begin at a particle source. At each half of each loop of the spiral path, the protons gain energy as they pass through an RF electric field in space 43. As the particles gain energy, the radius of the central orbit of each successive loop of its spiral path becomes larger than the previous loop until the loop radius reaches the maximum radius of the pole face. At that location, perturbations in the magnetic and electric fields direct the particles into an area where the magnetic field rapidly decreases, and the particles leave the high magnetic field area and are directed through an evacuated tube 46 (Figs. 2 and 3) (referred to herein as the extraction channel) and out of the yoke of the particle accelerator. A magnetic regenerator can be used to vary the perturbation of the magnetic field to direct the particles. Particles exiting the particle accelerator will tend to disperse as they enter an area of significantly reduced magnetic field that exists in the room around the particle accelerator. Beam shaping elements 48, 49 in the extraction channel 46 redirect the particles from the particle accelerator so that they remain within a straight beam of limited spatial extent.

[0068] As the beam exits the extraction channel, it is passed through a beam forming system (an example of which is described below with reference to Fig. 6), which can be programmably controlled to produce a desired combination of scanning, scattering, and / or range modulation for the output particle beam.

[0069] Ultra-high dose rate FLASH therapy may require higher average beam currents and instantaneous beam currents than non-FLASH applications. These higher average beam currents and instantaneous beam currents can be achieved using the techniques described herein. The particle accelerators, therapy systems, and variations thereof described herein can be configured and controlled to apply ultra-high dose rate radiation, such as FLASH rate, to an irradiation target within a patient. In this regard, experimental results of radiation therapy have shown improvements in the condition of healthy tissue exposed to radiation when the therapeutic dose is delivered at ultra-high (FLASH) dose rates. In one example, when delivering a radiation dose of 10-20 Gray (Gy) in a pulse less than 500 milliseconds (ms) and reaching an effective dose rate of 20-100 Gray per second (Gy / s), healthy tissue receives less damage than when irradiated with the same dose over a longer time scale, while tumors are treated with similar effectiveness. The theory that can explain this "FLASH effect" is based on the fact that radiation damage to tissue is proportional to the amount of oxygen supply in the tissue. In healthy tissue, ultra-high dose rates radicalize oxygen only once, as opposed to multiple oxygen radicalizations over a longer time scale with dose applications. This may lead to less damage in healthy tissue when using ultra-high dose rates.

[0070] In some examples, as described above, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gray per second over a duration of less than 500 ms. In some examples, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gray per second over a duration between 10 ms and 5 s. In some examples, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gray per second over a duration of less than 5 s.

[0071] In some examples, ultra-high dose rate radiation includes a dose of radiation that exceeds one of the following doses over a duration of less than 500 ms: 2 grays per second, 3 grays per second, 4 grays per second, 5 grays per second, 6 grays per second, 7 grays per second, 8 grays per second, 9 grays per second, 10 grays per second, 11 grays per second, 12 grays per second, 13 grays per second, 14 grays per second, 15 grays per second, 16 grays per second, 17 grays per second, 18 grays per second, 19 grays per second, 20 grays per second, 30 grays per second, 40 grays per second, 50 grays per second, 60 grays per second, 70 grays per second, 80 grays per second, 90 grays per second, or 100 grays per second. In some examples, ultra-high dose rate radiation includes a dose of radiation that exceeds one of the following doses over a duration between 10 ms and 5 s: 2 grays per second, 3 grays per second, 4 grays per second, 5 grays per second, 6 grays per second, 7 grays per second, 8 grays per second, 9 grays per second, 10 grays per second, 11 grays per second, 12 grays per second, 13 grays per second, 14 grays per second, 15 grays per second, 16 grays per second, 17 grays per second, 18 grays per second, 19 grays per second, 20 grays per second, 30 grays per second, 40 grays per second, 50 grays per second, 60 grays per second, 70 grays per second, 80 grays per second, 90 grays per second, or 100 grays per second. In some examples, ultra-high dose rate radiation includes a dose of radiation that exceeds one of the following doses over a duration of less than 5 s: 2 grays per second, 3 grays per second, 4 grays per second, 5 grays per second, 6 grays per second, 7 grays per second, 8 grays per second, 9 grays per second, 10 grays per second, 11 grays per second, 12 grays per second, 13 grays per second, 14 grays per second, 15 grays per second, 16 grays per second, 17 grays per second, 18 grays per second, 19 grays per second, 20 grays per second, 30 grays per second, 40 grays per second, 50 grays per second, 60 grays per second, 70 grays per second, 80 grays per second, 90 grays per second, or 100 grays per second.

[0072] In some examples, the ultra-high dose rate radiation includes a radiation dose exceeding one or more of the following doses over a duration of less than 500 ms, over a duration between 10 ms and 5 s, or over a duration of less than 5 s: 100 grays per second, 200 grays per second, 300 grays per second, 400 grays per second, or 500 grays per second.

[0073] In some examples, the ultra-high dose rate radiation includes a radiation dose between 20 grays per second and 100 grays per second over a duration of less than 500 ms. In some examples, the ultra-high dose rate radiation includes a radiation dose between 20 grays per second and 100 grays per second over a duration between 10 ms and 5 s. In some examples, the ultra-high dose rate radiation includes a radiation dose between 20 grays per second and 100 grays per second over a duration of less than 5 s. In some examples, the ultra-high dose rate radiation includes a radiation dose between 40 grays per second and 120 grays per second over a time period such as less than 5 s. Other examples of the time period are those provided above.

[0074] Referring to FIG. 6, an exemplary particle beam therapy system 82 that uses the accelerators and techniques described herein includes a gantry 84. The gantry 84 includes a ring-shaped or circular support structure 85 and a beam line structure 86. The combination of the support structure 85 and the beam line structure 86 can be referred to as a "compact gantry" due to its relatively small size. The beam line structure 86 includes an output channel 87 attached to the support structure 85 and a conduit 88 that directs a particle beam from the particle accelerator 10 to the output channel. The gantry 84 also includes one or more motors (not shown) for moving the output channel 87 around the support structure 85 relative to a treatment position 89. The treatment position can include a system isocenter where a patient can be positioned for treatment. In one example, the motor can move the output channel 87 along a track on the structure 85, resulting in rotation of the output channel 87 relative to the treatment position 89. In one example, the structure to which the output channel 87 is attached can rotate relative to the treatment position 89 in a couch 89a, resulting in rotation of the output channel 87 relative to the treatment position. In some implementations, the rotation enabled by the gantry 84 allows the output channel 87 to be positioned at any angle relative to the treatment position. For example, the output channel 87 can rotate through 360°, and as such, the output channel 87 can be positioned at 0°, 90°, 270°, and returned to 0° / 360°, or positioned at any angle between these rotational positions. As previously described, the beam line structure 86 is configured to direct a particle beam from the accelerator 10 to the treatment position 89. For this purpose, the output channel 87 includes magnets for bending the particle beam toward the treatment position. In addition, the beam line structure 86 includes a conduit 88 that includes magnets along a beam line that directs the particle beam from the particle accelerator 10 to the output channel 87.

[0075] The output channel includes magnetic dipoles arranged in series to bend the particle beam by at least 90°. The magnetic dipoles can include at least a first magnetic dipole and a second magnetic dipole. The magnets in the output channel can be configured to bend the particle beam by at least 90° towards the irradiation target in the presence of a magnetic field of at least 3 Tesla (T). In some examples, the output channel includes magnets for bending the particle beam by more than 90° (e.g., 100°, 110°, 120°, or more) towards the irradiation target.

[0076] A beam shaping system (which can include one or more scanning magnets, a range shifter composed of a plurality of plates movable into and out of the path of the particle beam, and a configurable collimator) can be included in the nozzle 90. In some implementations, one or more of the scanning magnets can be included in the beamline structure 86 and / or the output channel 87.

[0077] Another exemplary particle therapy system 120 that uses the accelerators and techniques described herein includes a gantry, as shown in FIG. 7. The gantry 94 can be connected to the floor 96 of the treatment room in a rotational or axial direction, allowing for controlled movement of the gantry 94 relative to the floor of the treatment room. In this example, the particle accelerator 10 is mounted on top of the gantry and is rotatable around the patient together with the gantry to direct the particle beam in the direction of arrow 121. The gantry 94 can include an arm 97 that runs along the length of the gantry 94 and reaches the floor 96 of the treatment room. The particle accelerator 10 and the connected beamline structure 98 are rotatably mounted to the arm 97. That is, the particle accelerator 10 and the connected beamline structure 98 are connected to the end 99 of the arm 97 such that the particle accelerator 10 and the connected beamline structure 98 can rotate in the direction of arrow 121 at the end 99. This rotation is separate from the gantry rotation described herein. The beamline structure can include magnets for bending the particle beam for application near the patient. For example, the beamline structure can include magnets for bending the particle beam more than 90° (e.g., 100°, 110°, 120°, or more) towards the irradiation target.

[0078] FIG. 12 shows a portion of an example of a proton therapy system 104 that includes a particle accelerator mounted on a gantry using the accelerators and techniques described herein. Since the accelerator is mounted on the gantry, the particle accelerator is either in or adjacent to the treatment room. In some implementations, the gantry is made of steel and has two legs (not shown) mounted for rotation on two respective bearings lying on opposite sides of the patient. The gantry can include a steel truss (not shown), the steel truss being connected to each of its legs, the legs being long enough to span the treatment area where the patient lies, and the legs being attached to the rotating legs of the gantry at both ends. The particle accelerator can be supported by the steel truss for movement around the patient. In the example of FIG. 12, the patient fits on a treatment couch 105. The treatment couch 105 includes a platform for supporting the patient.

[0079] The operation of the exemplary particle accelerators and particle therapy systems described herein, as well as the operation of all or some of their components, can be (at least partially) controlled using a control system 92 (FIGS. 6 and 7) configured to execute one or more computer program products (e.g., one or more computer programs tangibly embodied in one or more non-transitory machine-readable media) for execution by one or more data processing devices (e.g., programmable processors, computers, multiple computers, and / or programmable logic components) (for controlling the operation of the one or more data processing devices).

[0080] All or part of the systems and various modification examples described herein can be at least partially configured or controlled by one or more computers, such as a control system that uses one or more computer programs tangibly embodied in one or more information carriers (such as in one or more non-transitory machine-readable storage media). The computer program can be written in any form of programming language, including compiled languages or interpreted languages, and it can be deployed in any form (including as a stand-alone program or as modules, parts, subroutines, or other units suitable for use in a computing environment). The computer program can be deployed to be executed on one computer or on multiple computers at one site, or it can be distributed across multiple sites and interconnected by a network.

[0081] Actions associated with configuring or controlling the systems described herein can be performed by one or more programmable processors that execute one or more computer programs to control or implement all or some of the operations described herein. All or part of the systems and processes can be configured or controlled by special-purpose logic circuits, such as FPGAs (Field Programmable Gate Arrays) and / or ASICs (Application Specific Integrated Circuits), or built-in microprocessors localized in instrumentation hardware.

[0082] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, as well as any one or more processors of any kind of digital computer. In general, a processor will receive instructions and data from a read only storage area or a random access storage area or both. Elements of a computer will include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. In general, a computer will also include one or more machine-readable storage media, such as mass storage devices for storing data (e.g., magnetic disks, magneto-optical disks, or optical disks, etc.), or be operatively coupled to receive data from, or transfer data to, one or more machine-readable storage media, or both. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage areas, including, by way of example, semiconductor storage area devices, such as EPROM (erasable programmable read only memory), EEPROM (electrically erasable programmable read only memory), and flash storage area devices, magnetic disks, such as internal hard disks or removable disks, magneto-optical disks, and CD-ROM (compact disk read only memory) and DVD-ROM (digital versatile disk read only memory).

[0083] Elements of the different implementations described can be combined to form other implementations not specifically described previously. Elements can be removed from the previously described systems without overall adverse effect on their operation or on the operation of the system. Moreover, various separate elements can be combined into one or more individual elements to perform the functions described herein.

[0084] In the specification and claims provided herein, adjectives such as “first,” “second,” and “third” need not specify a priority or order unless the context otherwise indicates. Instead, these adjectives can be used only to differentiate the nouns they modify.

[0085] Any mechanical or electrical connection herein can include a direct physical connection or an indirect physical connection including one or more intervening components. The electrical connection can be wired and / or wireless.

[0086] Also, other implementations not specifically described herein are within the scope of the appended claims.

Description of Reference Numerals

[0087] 10 Superconducting synchrocyclotron 13 Superconducting coil 14 Superconducting coil 16 Magnetic yoke 17 Magnetic yoke 19 Magnetic cavity 20 Reverse stainless steel bobbin 21 Cryostat chamber 22 Support strap 24 Support strap 25 Particle source 26 Support strap 29 Arrow 31 Emitter side 32 Gas feed section 33a Cathode 33b Cathode 34 Reflector side 36 Tube 36a Tube 37 Active (RF) Dee 38 Acceleration region 38a Opening 40 Active deep plate 41 Semi-circular surface 42 Semi-circular surface 43 Space 44 Duct 45Dummy Dee 46 Tube, extraction channel 48 Beam shaping element 49 Beam shaping element 50 Minimum frequency 51 Maximum frequency 55 RF voltage waveform 56 Pulse 57 Start frequency 58 End frequency 60 RF voltage waveform 61 Slope 62 Particle injection 64 Slope 65 Particle injection 69 Pulse 70 Upper part of RF waveform 71 71 RF waveform 72 Pulse 74 Slope 75 Comparator circuit 76 D flip-flop 77 D flip-flop 78 NAND gate 79 Low-pass filter 80 Analog comparator 82 Particle therapy system 84 Gantry 85 Support structure 86 Beam line structure 87 Output channel 88 Conduit 89 Treatment location 89a Couch 90 Nozzle 92 Control system 94 Gantry 96 Floor of the treatment room 97 Arm 98 Beam line structure 99 End of arm 97 100 Pulse width, waveform width 101 Pulse height 102 Waveform width 104 Proton therapy system 105 Treatment couch 106 Waveform width 120 Valve, particle therapy system 120a Valve 120b Valve 121 Arrow 122 Arrow 124 Housing 125 Region 126 Piezoelectric actuator 127a Wire 127b Wire 128 Arrow 128a Arrow 129 Torlon seal 130 Coaxial seal 132 Region 133 Stationary wire 135 Location, gap 140 Particle source 142 Gas 143 Tube, chimney 144a Cathode 144b Cathode 146 Slit 147 Anode 148 Inlet 150 Arrow 1000 Deep plate 1003 Semi-circular surface, deep plate 1005 Semi-circular surface Area of the cavity 19 Inner conductor 1300 Outer conductor 1302 Power connection device 1304 Variable reactive element, rotary capacitor 1306 Capacitive structure, variable reactive element, capacitor 1308 Blade, rotary capacitor 1310 Plate 1312 Direction 1314 Surface 1316 Voltage source 1320 Distance D Frequency F1 Frequency F2 Signal Q1 Signal Q2

Claims

1. A particle accelerator comprising: a particle source for providing particles to a magnetic cavity; a circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from an ionized plasma in an orbit within the magnetic cavity, the RF voltage having a smaller slope when the particles are injected into the magnetic cavity than when the particles are accelerated within the magnetic cavity; an extraction channel for receiving the particles from the magnetic cavity for output as a particle beam from the particle accelerator; The particle accelerator comprising the above components. [[ID=?]]

2. [[ID=?]]The RF voltage has a first slope when the particles are injected into the magnetic cavity and a second slope when the particles are accelerated within the magnetic cavity, the first slope being smaller than the second slope at least during the RF voltage drop slope, according to the particle accelerator of Claim 1. [[ID=?]]

3. [[ID=?]]The particle accelerator according to Claim 2, wherein the first slope is at least 50% smaller than the second slope. [[ID=?]]

4. [[ID=?]]The particle accelerator according to Claim 2, wherein the first slope is at least 30% smaller than the second slope. [[ID=?]]

5. [[ID=?]]The particle accelerator according to Claim 2, wherein the first slope is at least 20% smaller than the second slope. [[ID=?]]

6. [[ID=?]]The particle accelerator according to Claim 1, wherein the slope that decreases when the particles are injected into the magnetic cavity corresponds to an increase in current in the particle beam. [[ID=?]]

7. [[ID=?]]The particle accelerator according to Claim 1, wherein the slope that decreases when the particles are provided to the magnetic cavity is proportional to an increase in current in the particle beam. [[ID=?]]

8. [[ID=?]]The particle accelerator according to Claim 1, further comprising an RF controller including a rotary capacitor for changing the RF voltage, the rotary capacitor including plates having a shape based on a target decrease in the RF voltage slope. [[ID=?]]

9. [[ID=?]]The particle accelerator according to Claim 1, wherein the particle beam is output at a FLASH dose. [[ID=?]]

10. [[ID=?]]The particle accelerator according to Claim 1, wherein the particle beam is output at a dose exceeding 20 Gray per second over a duration of less than 5 seconds. [[ID=?]]

11. [[ID=?]]A particle beam therapy system comprising: [[ID=?]]the particle accelerator according to Claim 1; A gantry configured to enable output of the particle beam to a patient, A particle beam therapy system including the same.

12. The gantry includes a conduit for transporting the particle beam, the conduit includes a magnetic dipole configured to bend the particle beam at least 90° toward the patient, and the magnetic dipole is mounted for rotation around the gantry. The particle beam therapy system according to claim 11.

13. The magnetic dipole is configured to bend the particle beam at least 90° in the presence of a magnetic field of at least 3 Tesla (T). The particle beam therapy system according to claim 12.

14. A system comprising: A particle source for providing particles to a magnetic cavity; A circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from the ionized plasma in an orbit within the magnetic cavity; A control system for controlling the particle source to provide the particles to the magnetic cavity based on the slope of the RF voltage; An extraction channel for receiving the particles from the magnetic cavity for output as a particle beam from the particle accelerator; A system including the same.

15. The control system is configured to control the particle source to provide the particles to the magnetic cavity at or near the top of a waveform including the RF voltage. The system according to claim 14.

16. The system further includes a comparator circuit for identifying a location at or near the top of the waveform representing the RF voltage. The system according to claim 15.

17. The control system is configured to control the particle source to provide the particles to the magnetic cavity between a first waveform generated for an injection cycle and a second waveform generated for an acceleration cycle, where the first waveform has an increased waveform width compared to the second waveform. The system according to claim 14.

18. The control system is configured to control the particle source to provide the particles to the magnetic cavity at or near the top of a waveform generated for an injection cycle. The system according to claim 14, wherein the waveform generated for the injection cycle has an increased waveform width with respect to the waveform generated for the acceleration cycle.

19. The system according to claim 14, wherein the particle beam is output at a FLASH dose.

20. The system according to claim 14, wherein the particle beam is output at a dose exceeding 20 Gy per second over a duration of less than 5 seconds.

21. The system according to claim 14, further comprising a gantry configured to enable output of the particle beam to a patient.

22. The gantry according to claim 16 includes a conduit for transporting the particle beam, the conduit including a magnetic dipole configured to bend the particle beam at least 90° toward the patient, the magnetic dipole being mounted for rotation around the gantry.

23. The particle therapy system according to claim 22, wherein the magnetic dipole is configured to bend the particle beam at least 90° in the presence of a magnetic field of at least 3 Tesla (T).

24. A particle source, a tube for introducing gas into a region where particles are to be accelerated, the tube having an opening through which the particles are released into the region, electrodes at different ends of the tube for applying a potential to ionize the gas and thereby create the particles, a valve controllable to allow the gas to reach the opening or to prevent the gas from reaching the opening, comprising a particle source.

25. The particle source according to claim 24, wherein the valve is in the tube and closer to the opening than either of the electrodes.

26. The particle source according to claim 24, wherein the valve includes a piezoelectric displacement valve.

27. The pressure of the gas in the tube is 10 －４ Torr (0.0133322 Pascal (Pa)) or more, the particle supply source according to claim 24.

28. Ionizing the gas creates a plasma in the tube, the plasma having at least a predefined particle density, according to the particle source of claim 24.

29. The predefined particle density is 10 １５ ions / cm ３ The particle source according to claim 28, wherein the particle source is such that

30. The particle source according to claim 24, wherein the valve is located 3 centimeters (3 cm) or less from the opening.

31. The valve is at 2 centimeters (2 cm) or less from the opening, the particle supply source according to claim 24.

32. The valve is between 1 centimeter (1 cm) and 4 centimeters (cm) from the opening, the particle supply source according to claim 24.

33. The electrode includes a cathode, the cathode is periodically charged, thereby creating an electrical pulse, the electrical pulse ionizes the gas to create a plasma, and emits the particles into the region, the particle supply source according to claim 24.

34. The electrical pulse is created every 1 millisecond or more over a duration on the order of single-digit microseconds, the particle supply source according to claim 33.

35. The tube is completely separated in the region, the particle supply source according to claim 24.

36. The tube includes an opening in the region, but is not completely separated in the region, the particle supply source according to claim 24.

37. A system comprising: A particle supply source for providing particles to a magnetic cavity; A circuit for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate the particles in an orbit within the magnetic cavity; A control system for controlling the particle supply source to provide the particles to the magnetic cavity; Including: The particle supply source is: A tube for introducing gas into a region of the magnetic cavity where the particles are to be accelerated, the tube has an opening, and the particles are emitted into the region through the opening; Electrodes on different sides of the opening for applying a potential to ionize the gas and thereby create the particles; A valve that is controllable to allow the gas to reach the opening or to prevent the gas from reaching the opening; A system including.

38. The gas in the tube is under a first pressure, the magnetic cavity is at a second pressure lower than the first pressure, and the valve is controllable to reduce the influence of the first pressure in the tube on the second pressure in the magnetic cavity, the system according to claim 37.

39. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to prevent gas from reaching the opening during the time when the potential is not applied to the electrode, the system according to claim 37.

40. The electrode includes a cathode, the cathode is periodically charged, thereby creating an electrical pulse, the electrical pulse ionizes the gas to create a plasma, and releases the particles into the region. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to prevent gas from reaching the opening during at least a portion of the time when the electrical pulse is not created, the system according to claim 37.

41. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to allow gas to reach the opening when the potential is applied to the electrode, the system according to claim 37.

42. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to allow gas to reach the opening only when the potential is applied to the electrode and only for a predetermined duration prior to the potential being applied to the electrode, the system according to claim 37.

43. The electrode includes a cathode, the cathode is periodically charged, thereby creating an electrical pulse, the electrical pulse ionizes the gas to create a plasma, and releases the particles into the region. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to allow gas to reach the opening during the time when the electrical pulse is created, the system according to claim 37.

44. The electrode includes a cathode, the cathode is periodically charged, thereby creating an electrical pulse, the electrical pulse ionizes the gas to create a plasma, and emits the particles into the region. The gas in the tube is under a first pressure, the magnetic cavity is under a second pressure that is less than the first pressure, and the valve is controllable to allow gas to reach the opening only during the time the electrical pulse is created and only for a predetermined duration prior to the creation of the electrical pulse. The system according to claim 37.

45. The valve is in the tube and is closer to the opening than any of the electrodes. The particle source according to claim 37.

46. The valve includes a piezoelectric displacement valve. The particle source according to claim 37.

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