Device for controlling beam current intensity in synchrocyclotron

Abstract

An exemplary particle accelerator includes a particle source to provide particles to a magnetic cavity; circuitry to provide a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from the ionized plasma on the track in the magnetic cavity, where the RF voltage has a slope that is less than the slope of the particles when accelerated in the magnetic cavity when the particles are injected into the magnetic cavity; and the extraction channel is used for receiving the particles from the magnetic cavity and outputting the particles as particle beams from the particle accelerator.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 392,264, filed on July 26, 2022. The contents of U.S. Provisional Application No. 63 / 392,264 are incorporated herein by reference. Technical Field

[0003] This specification describes examples of techniques for controlling beam current intensity in a particle accelerator. Background Art

[0004] Particle therapy systems use particle accelerators to generate particle beams for treating irradiated targets, such as tumors. One property of a particle beam is its beam current or beam intensity. Beam current is a function of the number of particles injected into the particle accelerator. Higher beam currents allow for higher dose rates to be delivered to the target. Summary of the invention

[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 on a track in the magnetic cavity, wherein when the particles are injected into the magnetic cavity, the slope of the RF voltage is less than the slope when the particles are accelerated in the magnetic cavity; and an extraction channel for receiving particles from the magnetic cavity to be output from the particle accelerator as a particle beam. The particle accelerator may include one or more of the following features, either alone or in combination.

[0006] When the particles are injected into the magnetic cavity, the RF voltage may have a first slope, and when the particles are accelerated in the magnetic cavity, the RF voltage may have a second slope. At least during the period when the RF voltage is decreased, the first slope may be less than the second slope. The first slope may be at least 50% less than the second slope. The first slope may be at least 30% less than the second slope. The first slope may be at least 20% less than the second slope. When the particles are injected into the magnetic cavity, the smaller slope may correspond to an increase in the current in the particle beam. When the particles are provided to the magnetic cavity, the smaller slope may be proportional to the increase in the current in the particle beam.

[0007] The particle accelerator may include an RF controller including a rotation capacitor to vary the RF voltage. The rotation capacitor may include a plate having a shape that decreases based on a target slope of the RF voltage. The particle beam may be output at a FLASH dose rate, such as a dose exceeding twenty (20) grays per second in a duration of less than five (5) seconds.

[0008] An exemplary particle therapy system includes the aforementioned particle accelerator and a gantry configured to output a particle beam to a patient. The gantry may include a channel for delivering the particle beam. The channel may include a dipole magnet configured to bend the particle beam at least 90° toward the patient. The dipole magnet may be mounted to rotate around the gantry. The dipole magnet may 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 example 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 from an ionized plasma on a track in the magnetic cavity; a control system for controlling the particle source based on the slope of the RF voltage to provide particles to the magnetic cavity; and an extraction channel for receiving particles from the magnetic cavity to be output from the particle accelerator as a particle beam. The example system may include one or more of the following features, alone or in combination.

[0010] The control system may be configured to control the particle source to provide particles to the magnetic cavity at or near the top of a waveform comprising an RF voltage. The system may include a comparator circuit to identify a position near the top of or near the top of a waveform representing the RF voltage. The control system may be configured to control the particle source to provide particles to the magnetic cavity during an RF voltage having a first waveform generated for an injection period, the first waveform having an increased waveform width relative to a second waveform generated for an acceleration period. The control system may be configured to control the particle source to provide particles to the magnetic cavity at or near the top of a waveform generated for an injection period. The waveform generated for the injection period may have an increased waveform width relative to the waveform generated for the acceleration period.

[0011] The particle beam can be output at a FLASH dose rate. The particle beam can be output at a dose of more than twenty (20) grays per second for a duration of less than five (5) seconds. The system can include a gantry configured to enable the particle beam to be output to a patient. The gantry can include a channel for delivering the particle beam. The channel can include a dipole magnet configured to bend the particle beam toward the patient by at least 90°. The dipole magnet can be mounted to rotate around the gantry. The dipole magnet 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 comprises: a tube for introducing a gas into a region where particles are to be accelerated, wherein the tube has an opening through which the particles are released into the region; electrodes at different ends of the tube for applying an electrical potential to ionize the gas and thereby produce the particles; and a valve controllable to allow or prevent the gas from reaching the opening. The particle source may include one or more of the following features, alone or in combination.

[0013] The valve may be within the tube and may be closer to the opening than to any of the electrodes. The valve may comprise a piezoelectric displacement valve. The pressure of the gas within the tube may be 10 -4 Torr (0.0133322 Pascal (Pa)) or greater. Ionizing the gas may generate a plasma in the tube. The plasma may have at least a predefined particle density. The predefined particle density may be 10 15 ions / cm 3 . The valve may be three centimeters (3 cm) or less from the opening. The valve may be two centimeters (2 cm) or less from the opening. The valve may be between one centimeter (1 cm) and four centimeters (cm) from the opening. The electrode may include a cathode that is periodically charged, thereby generating an electrical pulse that ionizes the gas to produce a plasma and discharge particles into the region. The electrical pulses may be generated every millisecond or longer for a duration on the order of single-digit microseconds. The tube may be completely separated at the region. The tube may include an opening at the region, but not completely separated at the region.

[0014] An example 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 on a track in the magnetic cavity; and a control system that controls the particle source to provide particles to the magnetic cavity. The particle source includes a tube for introducing a gas into a region of the magnetic cavity where particles are to be accelerated, wherein the tube has an opening through which particles are released into the region; electrodes on different sides of the opening for applying an electric potential to ionize the gas and thereby generate particles; and a valve that can be controlled to allow or prevent the gas from reaching the opening. The system can include one or more of the following features, either individually or in combination.

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

[0016] The electrode may include a cathode that is periodically charged, thereby generating an electrical pulse that ionizes the gas to generate plasma and release particles into the region. The gas in the tube may be at a first pressure, and the magnetic cavity may be at a second pressure that is different from (e.g., less than) the first pressure. The valve may be controllable to prevent the gas from reaching the opening at least part of the time when the electrical pulse is not generated. The valve is controllable to allow the gas to reach the opening when the potential is applied to the electrode. The valve is controllable to allow the gas to reach the opening only when the potential is applied to the electrode and only within a predetermined duration before the potential is applied to the electrode.

[0017] The electrode may include a cathode that is periodically charged, thereby generating an electrical pulse that ionizes the gas to generate a plasma and release particles into the region. The gas in the tube may be at a first pressure, and the magnetic cavity may be at a second pressure that is less than the first pressure. The valve may be controllable to allow the gas to reach the opening during the generation of the electrical pulse. The valve may be controllable to allow the gas to reach the opening only during the generation of the electrical pulse and only for a predetermined duration before the generation of the electrical pulse. The valve may be in the tube and closer to the opening than either electrode. The valve may include a piezoelectric displacement valve.

[0018] Any two or more features described in this specification (including this Summary) may be combined to form embodiments not specifically described in this specification.

[0019] The control of the various systems or parts thereof described herein can be implemented via a computer program product, which includes instructions stored on one or more non-transitory machine-readable storage media and executable on one or more processing devices (e.g., microprocessors, application-specific integrated circuits, programming logic such as field programmable gate arrays, etc.). The systems or parts thereof described herein can be implemented as an apparatus, method, or medical system, which can include one or more processing devices and computer memory to store executable instructions to implement control of the functions described. The apparatus, systems, and / or components described herein can be configured, for example, by design, construction, arrangement, placement, programming, operation, activation, deactivation, and / or control.

[0020] The 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] Figure 1 is a cross-sectional side view of components of an exemplary particle accelerator that may be used with the particle therapy systems described herein.

[0022] Figure 2 is an exploded view showing the components of a particle accelerator.

[0023] Figure 3 is a cross-sectional top view showing components of a particle accelerator.

[0024] Figure 4 is a cut-away side view of an exemplary particle source that may be used in a particle accelerator.

[0025] Figure 5 is a perspective view of an exemplary radio frequency (RF) that may be used in a particle accelerator.

[0026] Figure 6is a perspective view of an exemplary particle therapy system that may include a particle accelerator.

[0027] Figure 7 is a perspective view of another exemplary particle therapy system that may include a particle accelerator.

[0028] Figure 8 is a graph showing RF waveforms that may be used during an acceleration period in a particle accelerator.

[0029] Fig. 9 is a graph showing RF waveforms that may be used during a particle injection cycle in a particle accelerator.

[0030] Fig.10 is a graph showing RF waveforms that may be used during a particle injection cycle in a particle accelerator.

[0031] Fig.11 is a circuit diagram of an exemplary comparator circuit.

[0032] Fig.12 is a perspective view of an exemplary particle therapy system that may include a particle accelerator.

[0033] Fig.13 is a cut-away side view of example components, including circuitry, for controlling the amplitude and waveform of a frequency sweep in a particle accelerator.

[0034] Fig.14 is a cross-sectional side view of an exemplary valve that may be used in a particle source to regulate gas flow to a source opening.

[0035] Fig.15 is a cross-sectional side view of another exemplary particle source that may be used in a particle accelerator.

[0036] The same reference numbers in different drawings denote the same elements. DETAILED DESCRIPTION

[0037] Described herein is an exemplary particle therapy system and a particle accelerator used therewith, which is configured to produce beam current and particle beam intensity that can be used for ultra-high dose rate or FLASH particle therapy. Generally, the system and accelerator described herein are controllable to increase the amount of protons or ions (commonly referred to as "particles") injected into the particle accelerator, for example, the quantity, so as to affect (for example, increase) the beam current. In some embodiments, the system is configured to change the frequency of the radio frequency (RF) voltage supplied to the particle accelerator so as to increase the time period during which the particles are injected into the accelerator and accepted by the accelerator. In some embodiments, the system is configured to select a point with a minimum or relatively small slope on the RF waveform, and then inject the particles into the accelerator. The effect is to increase the time period during which the particles are injected into the accelerator and accepted by the accelerator. The increase in the amount of particles accepted by the accelerator leads to an increase in beam current. In some embodiments, the system is configured to adjust the pressure inside the particle accelerator so as to reduce the impact of collision particle losses.

[0038] Figure 1 A cross section of a component of an exemplary superconducting synchrocyclotron 10 is shown, which can be used to provide a particle (e.g., proton) beam in a particle (e.g., proton) therapy system having one or more features of the type described in the previous paragraph. In this example, the component includes a superconducting magnet. The superconducting magnet includes superconducting coils 13 and 14. The superconducting coils are formed by a plurality of integrated conductors, each of which includes a superconducting strand, for example, four or six strands, wound around a central strand, which itself can be superconducting or non-superconducting. Each superconducting coil 13, 14 is used to conduct an electric current that generates a magnetic field (B). Magnetic yokes 16, 17 or smaller pole pieces form a magnetic field in a magnetic cavity (referred to herein as a "cavity") 19, and particles are accelerated in the magnetic cavity 19. In one example, a cryostat (not shown) uses liquid helium (He) to conduct each coil to a low-temperature superconducting temperature, for example, about 4 Kelvin (K).

[0039] like Figure 2 As shown, two superconducting magnet coils 13, 14 are centered on a common axis and spaced apart along the axis. The coils may be made of Nb3S n The base superconducting strand is formed. The coil is mounted on an inverted stainless steel bobbin 20. The geometry of the coil is maintained by the inverted stainless steel 20, which applies a restoring force that counteracts the twisting force or hoop force generated when the coil is energized.

[0040] The superconducting coils are maintained at a temperature close to absolute zero (e.g., about 4K) by enclosing the coil assembly (coils and bobbins) within a vacuum annular aluminum or stainless steel cryostat chamber 21, which provides free space around the coil structure except at a limited set of support points. The coil assembly and cryostat chamber are mounted within and completely enclosed by yokes 16 and 17, which together can be considered a single yoke. The yokes provide a path for the return magnetic field flux and magnetically shield the volume between the yoke pole faces to prevent external magnetic influences from perturbing the magnetic field shape within the cavity. The yokes also serve to reduce stray magnetic fields near the accelerator.

[0041] like Figure 3 As shown, a set of support straps 22, 24, 26, which range from warm to cold, are used to maintain the position of the coils relative to the yoke and cryostat. Supporting the bobbin and coils with the straps reduces heat leakage transferred to the cryostat by the rigid support system. The straps are arranged to withstand the varying gravitational forces on the coils. When they are disturbed from a completely symmetrical position relative to the yoke, they withstand the combined effects of gravity and the large eccentric forces generated by the coils. In addition, as the position of the gantry changes, as the gantry accelerates and decelerates, the straps serve to reduce the dynamic forces exerted on the coils.

[0042] In some embodiments, such as Figures 1 to 3 In the illustrated embodiment, a magnetic shield (not shown) surrounds the yoke. The return yoke and shield together function to reduce stray magnetic fields, thereby reducing the likelihood that stray magnetic fields will adversely affect the operation of the particle accelerator.

[0043] In some embodiments, the return yoke and / or shield can be replaced or enhanced by an active return system. An exemplary active return system includes one or more active return coils that conduct current in the opposite direction to the current through the main superconducting coils 13, 14. In some embodiments, there is one active return coil for each superconducting main coil, for example, two active return coils, one for each main superconducting coil. Each active return coil can also be a superconducting coil that concentrically surrounds the outside of the corresponding main superconducting coil. In some specific embodiments, the active return coil can be a non-superconducting coil or include a non-superconducting coil. By using an active return system, the relatively large ferromagnetic yokes 16, 17 can be replaced with smaller and lighter pole pieces. Therefore, 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 U.S. Patent No. 8,791,656 (Zwart), entitled "Active Return System". The contents of U.S. Patent No. 8,791,656, particularly those related to the return coil construction (e.g., the contents of U.S. Patent No. 8,791,656) are described in detail. Figure 2 , 4and 5 and the accompanying description) are incorporated herein by reference.

[0044] Another component of an accelerator is the source of particles to be accelerated, called a particle source. For electron accelerators, various cathode technologies such as thermionic emitters, field emitters, and photocathodes easily provide a sufficient number of electrons for the beam. These electron sources also add minimal gas load to the accelerator vacuum system. However, proton and other ion accelerators can use more complex particle sources because ions cannot be removed from bulk metals as easily as electrons. Particle sources can take many forms, including sputtering sources and laser-driven sources. One class of particle sources is plasma-based particle sources. This type 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.

[0045] Exemplary plasma-based particle sources include Figure 1 , 3 and a particle source 25 of 4. In this example, the particle source 25 is a Penning ion source (PIG source) and is configured to provide a plasma column that is at least partially ionized within the cavity 19. Figure 1 and Figure 3 , the particle source 25 is close to the magnetic center of the synchrocyclotron so that the particles are present at the mid-plane of the synchrocyclotron where they can be subjected to the RF voltage field, as described below.

[0046] As mentioned above, the particle source may have a PIG geometry. In the PIG geometry, two high voltage electrodes, such as cathodes 33a, 33b ( Figure 4 ) are arranged at different or opposite ends of the particle source so that they are aligned linearly. For example, one cathode 33a can be on one side of the acceleration region 38, while the other cathode 33b can be on the other side of the acceleration region 38 and in line with the magnetic field lines in the chamber 19. A gas tube 36, sometimes referred to as a "chimney", extends from each end of the particle source to the acceleration region. In an embodiment where the particle source is not interrupted (see, for example, the following description) Fig.15 ), the tube extends through the acceleration region. The particle source 25 includes an emitter side 31 and a reflector side 34, and the emitter side 31 includes a gas feed port 32 for receiving gas. The gas is introduced through the gas feed port 32 and propagates in the direction of arrow 29 to and through the tube 36, which contains the gas. When a relatively small amount of gas (such as hydrogen / H2) occupies the area between the cathodes in the tube, a plasma column is formed by the gas by applying a voltage to the cathode. The applied voltage causes electrons to flow along magnetic field lines that are substantially parallel to the tube wall and ionizes the gas molecules concentrated in the tube. The background magnetic field prevents scattering of the ionized gas particles and produces a plasma column between the cathodes.

[0047] The gas in the gas tube may include a mixture of hydrogen and one or more other gases. For example, the mixture may contain hydrogen and one or more rare gases, such as helium, neon, argon, krypton, xenon and / or radon (although the mixture is not limited to use with rare gases). In some embodiments, the mixture may be a mixture of hydrogen and helium. For example, the mixture may contain about 75% or more hydrogen and about 25% or less helium (including possible trace gases). In another example, the mixture may contain about 90% or more hydrogen and about 10% or less helium (including possible trace gases). In the example, the hydrogen / helium mixture may be any of the following: >95% / <5%, >90% / <10%, >85% / <15%, >80% / <20%, >75% / <20%, etc.

[0048] As mentioned above, Figure 4 An example of a particle source 25 having a PIG geometry that may be used in a synchrocyclotron 10 is shown in FIG. 1 . Example implementations of a particle source 25 are also described in U.S. Pat. No. 8,970,137. The contents of U.S. Pat. No. 8,791,656, particularly with respect to interrupted particle sources (e.g., the contents of U.S. Pat. No. 8,970,137) are disclosed herein. Figure 3 A, 3B and 4 to 7 and the accompanying descriptions) are incorporated herein by reference.

[0049] The particle source can pass through the virtual D-shaped plate ( Figure 4 19) and is adjacent to an active (RF) dee plate 37, which will be described below. In operation, a particle source is periodically pulsed to provide particles (e.g., protons) to the cavity 19. The magnetic field between the active dee plate and the dummy dee plate accelerates the particles outward. The acceleration is spiral to produce an orbit around the plasma column, wherein the radius of the particle to the plasma column gradually increases. 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 is difficult to impart enough energy to the particle so that the particle has a sufficiently large radius of curvature to clear the physical shell of the particle source during the initial rotation during the acceleration process.

[0050] The magnetic field is relatively high in the central region of the cavity 19 containing the particle source, for example, about 2 Tesla (T) or higher (for example, 2.5T, 3T, 4T, 5T, 6T, 8T, 8.8T, 8.9T, 9T, 10.5T or higher). Due to this relatively high magnetic field, for low-energy particles, the radius of the initial particle to the ion source is relatively small, wherein the low-energy particle includes the particles first extracted from the plasma column. For example, such a radius can be on the order of 1mm (millimeter). Because the radius is so small, at least at the beginning, some particles may contact the shell of the particle source, thereby preventing these particles from further accelerating outward. Therefore, the shell of the particle source 25 can be interrupted, for example, separated to form two parts. That is, a part of the shell of the particle source can be partially or completely removed at the acceleration region 38, thereby generating an opening 38a around the region where the particle is output from the particle source. The shell can also be removed within the distance above and below the acceleration region. For example, the shell can also be removed in the acceleration region up and down by a single digit millimeter or a single digit centimeter.

[0051] In other words, the opposite portion of the particle source 25 that is aligned with the axis of rotation of the beam is separated so that the tip of the particle source does not reach the acceleration region 38. This design results in a relatively high conductivity between the plasma and the chamber (vacuum space). In the example, the particle source ideally produces a density of 10 15 Ions / cm 3 or 10 15 Electron / cm 3 (cubic centimeters) or larger plasma. If the pressure in the particle source is too low, the plasma density is too low, and the total beam current is limited by the number of protons that can be drawn 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 can increase the pressure of the cavity 19, adversely affecting particle acceleration, as described below. In addition, when the pressure in the particle source is too high, there are protons that can be drawn from the plasma, but the total beam current of the accelerator is limited by the collision losses of these protons caused by the background gas from the particle source. This may cause the performance of both the particle accelerator and the particle source to degrade.

[0052] In this regard, in some examples, a plasma-based particle source such as particle source 25 may be at or near 10 -4 In some embodiments, when the negative pressure is close to vacuum, for example, 10 -5Particle acceleration and beam transport in cavity 19 work better or best at 1000 torr (0.0013332 Pascal) or less. As the pressure in cavity 19 increases above vacuum, 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 gas pressures required for the plasma particle source can cause the beam line to be scattered and lost during transport, thereby limiting the beam current intensity that a synchrocyclotron can produce.

[0053] Therefore, the pressure in the particle source (e.g., particle source 25) greater than the pressure in the cavity 19 will increase the pressure in the cavity 19, thereby causing the size of the beam current intensity to be limited and other undesirable effects, including those mentioned above. In order to solve these problems, the particle source 25 is configured and controllably limits the pressure of the cavity exposed to the particle source. To this end, the particle source 25 includes a valve 120, such as a fast pulse gas valve, which regulates 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 of the particle source exposed to the gas leading to the cavity. Reducing the cavity from being exposed to the gas from the particle source will reduce the pressure of the cavity exposed to the particle source. As a result, the chance of the pressure increase in the cavity is also reduced due to exposure to the particle source pressure. In the example, the valve is controllable to prevent the gas from reaching the particle source opening 38a during the period when the cathode electric pulse (e.g., electric potential) is not generated, and allows the gas to reach the opening 38a when the electric pulse is generated and applied to the cathode. The valve is also controllable to allow the gas to reach the opening 38a within a predetermined duration before the electric pulse is generated and applied to the cathode. In some cases, the valve is controllable to allow gas to reach 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 opening 38a.

[0054] As shown, valve 120 is included in pipe 36, and pipe 36 provides gas to opening 38a in the acceleration area. In this example, valve 120 is located in the gas flow path towards opening 38a and is located on one side of the opening. When closed, the valve produces an airtight seal in pipe 36, preventing gas from flowing through the valve. When opened, the valve allows gas to flow through the valve and flow through the entire pipeline length (including the separation area) between the two cathodes.

[0055] In an example, a piezoelectric actuator controls valve 120. When the control system requests an ion pulse, the valve opens and allows gas to flow into tube 36 to produce a plasma column with a target high plasma density. This enables each bunching moving through the cavity to extract a large number of protons. Because, in some examples, the valve is opened only during the duration of particle injection, the amount of gas provided to the cavity by the particle source (called "gas load") can be reduced compared to a source that allows gas to flow continuously in the particle source until the accelerator is ready to produce a beam. This reduces the pressure provided to the cavity by the particle source. In some examples, the particle source is less than 2% of the time that the accelerator is operable to produce a particle beam. This can cause the pressure in the cavity to be reduced by more than an order of magnitude relative to an accelerator in which the particle source is always active and always provides gas and pressure to the cavity.

[0056] In this example, valve 120 is a piezoelectric displacement valve; however, other types of piezoelectrically actuated valves or electromechanical valves may be used. Fig.14 1 shows an example of a piezoelectric displacement valve 120a that can be used as a valve 120 in a particle source, such as particle source 25. In this example, valve 120a is connected to tube 36a, which can have Figure 4 The structure and function of tube 36 of FIG. 1 is that gas flows through tube 36 a in the particle source in the direction of arrow 122 toward the particle source opening. When closed, valve 120 a forms an airtight seal within tube 36 a; and, when open, valve 120 a allows gas to flow through the valve and into and toward the acceleration region and particle source opening, such as Figure 4 12a. The valve 120a includes a housing 124 that contains an area 125 through which gas passes when the valve 120a is open. 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 direction of arrows 128, 128a. The valve 120a also includes a torlon seal 129 physically connected to the piezoelectric actuator 126 and a coaxial seal 130 within the torlon seal. The valve 120a includes an area 132 through which gas is output from the valve 120a from the area 125 and a fixed wire 133, which can also receive electrical signals to affect the operation of the piezoelectric actuator 126.

[0057] Reference again Figure 4, valve 120 can be located at a position closer to opening 38a than any one of cathodes 33a and 33b. By positioning valve 120 to be closer to opening than any cathode, during the operation of the particle source, that is, when the valve is opened, the time spent by gas to reach opening 38a can be reduced, so that the particle source can generate pulses at a higher speed. That is, the gas does not need to travel too far to reach the opening, so that the particle source can run at a faster speed. In an example, valve 120 is three centimeters (3cm) or less from opening 38a. In an example, valve 120 is two centimeters (2cm) or less from opening 38a. In an example, valve 120 is between one centimeter (1cm) and four centimeters (cm) from opening 38a. Typically, valve 120 can be at any appropriate distance from opening 38a. The position of the valve can be based in part on its size. That is, the valve should be small enough to fit close to the opening without blocking the opening.

[0058] exist Fig.14 In the example valve of, the control system control circuit (not shown) periodically provides an electrical signal to the wires 127a, 127b. The electrical signal is consistent with the time when the particle source provides the pulse. For example, the cathode can be periodically charged to generate an electrical pulse that ionizes the gas to generate a pulsed plasma and release the particles into the chamber 19. The electrical pulses applied to the cathode can be generated once every millisecond or longer, and the duration is about the order of a single-digit microsecond (1μs to 9μs, although these numbers are only examples). The electrical signal provided to the piezoelectric actuator 126 can be a predetermined amount of time before these electrical pulses, which can also be measured in single-digit microseconds to ensure that when the electrical pulse is applied to the cathode, there is gas at the opening of the particle source. The electrical signal provided to the piezoelectric actuator 126 also extends to the entire duration of the electrical pulse applied to the cathode to ensure that the gas remains at the opening of the particle source during the entire time when the electrical pulse is applied to the cathode. In other words, shortly before an electrical pulse is applied to the cathode, an electrical signal is provided to the piezoelectric actuator 126 to open the valve 120 so that there is time for the gas to pass through the valve and fill the entire tube, including at the opening 38a, before the cathode is pulsed. The valve is controlled to remain open for the entire duration that the cathode is pulsed to ensure that the gas is retained to produce an ionized plasma column in the particle source. When the potential is removed from the cathode or shortly thereafter, the valve 120a is closed by stopping the electrical signal to the wires 127a and 127b.

[0059] In this regard, when an electrical signal is applied to wires 127a, 127b, piezoelectric actuator 126 contracts in the direction of arrows 128, 128a. This contraction also causes torlon seal 129 and coaxial seal 130 to move in the direction of arrow 128a, because they are physically connected to piezoelectric actuator 126 and move with it. These movements of various valve components create a path for gas to pass through the gap generated at position 135 when the piezoelectric actuator contracts from region 125, pass through region 132, flow out of valve 120a therefrom and enter the remainder of the particle source tube (including the region containing opening 38a). Because actuator 126 is piezoelectrically activated, actuator 126 can operate at a speed of the order of single-digit microseconds, although it may be slower than in some embodiments in operation. Therefore, valve 120a can be opened and closed at the order of single-digit microseconds, although it may be slower than in some embodiments in operation. To close valve 120a, the electrical signal is removed from wires 127a, 127b, which causes piezoelectric actuator 126 to expand in the direction of arrow 129. This expansion closes gap 135, thereby preventing gas from flowing out of the valve.

[0060] Thus, valve 120 / 120a is controllable to reduce the duration that 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 explained, valve 120 / 120a is controllable to prevent gas from reaching the opening during periods when an electrical pulse (potential) is not applied to the electrode, and therefore, the pressure from the tube / particle source does not reach the opening during those times and affect (e.g., increase) the pressure in the cavity.

[0061] Fig.15 Another example of a particle source 140 is shown, which can be used in the particle accelerator described herein and can include a valve, such as valve 120b, to control the flow of gas 142 within a tube (or chimney) 143 of the particle source. The particle source 140 includes cathodes 144a and 144b at opposite or different ends or portions thereof, the cathodes 144a and 144b being electrically pulsed to produce a partially ionized plasma from the gas, and the particle source 140 includes a slit 146, which is an opening from which a pulse of charged particles is released into a magnet such as cavity 19. Anode 147 is at ground potential. Gas is introduced into the particle source via inlet 148 and travels to valve 120b in the direction of arrow 150 when valve 120b is closed, and passes through valve 120b when valve 120b is open.

[0062] Valve 120b is Figure 4 An example embodiment of the valve 120 may have Fig.14The structure and function of valve 120 and valve 120a. 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 is controllable to prevent gas from reaching slit 146 during a period when a cathode electrical pulse (e.g., an electrical potential) is not generated, and allows gas to reach slit 146 when an electrical pulse is generated and applied to the cathode. The valve is also controllable to allow gas to reach slit 146 within a predetermined duration before the electrical pulse is generated and applied to the cathode. In some cases, the valve is controllable to allow gas to reach slit 146 only during the period when the electrical pulse is generated and applied to the cathode and only within a predetermined duration before the electrical pulse is generated. As described above, the particle source is thus able to output particle pulses to the chamber while reducing, minimizing, or substantially eliminating the effect of the pressure in the particle source on the pressure in the chamber.

[0063] The cavity 19 where acceleration occurs encloses the RF D-shaped plate and the dummy D-shaped plate and the particle source, and is evacuated by a vacuum pump. Maintaining a high vacuum / very low pressure ensures that the accelerated particles will not be lost due to collisions with gas molecules, and enables 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 to accelerate the particles generated from the plasma column pulse generated by the particle source. As noted, in the example, the particle accelerator is a synchrocyclotron. Therefore, the RF voltage is scanned over a frequency range to address relativistic effects on the particles, such as increasing the particle mass when accelerating particles in the cavity 19. The RF voltage drives the active D-shaped plate (described below) contained in the cavity, and has a frequency that is scanned downward during the acceleration cycle to address the problem of increased relativistic mass of protons and small demagnetization magnetic fields. The dummy D-shaped plate is used as a ground reference for the D-shaped plate. The magnetic field generated by passing a current through the superconducting coil together with the scanning RF voltage accelerates the particles from the plasma column along the track in the cavity, and increases the energy as the number of turns increases. The particles in the outermost orbit are guided to the extraction channel described below and output from the synchrocyclotron as a particle beam. In the synchrocyclotron, the particle beam is pulsed so that a particle bunch is output periodically.

[0064] exist Figure 5 and Fig.13 In the example of FIG. 1 , the active D-shaped plate 40 ( Fig.131000 in the figure is a hollow metal structure having two semicircular surfaces 41, 42 surrounding a space 43 in which protons are accelerated during rotation. A conduit 44 leading to the space 43 extends through the yoke to an external location from which a vacuum pump (not shown) can be attached to evacuate the space 43 and the remaining space within the cavity 19 where acceleration occurs. In this example, a dummy D-shaped plate 45 comprises a rectangular metal ring spaced close to the exposed edge of the D-shaped plate 40. The dummy D-shaped plate is grounded to the vacuum chamber and the yoke. The D-shaped plate 40 is driven by an RF signal applied to the end of a radio frequency transmission line to apply an electric field in the space 43. The frequency of the RF signal decreases over time during the particle acceleration cycle as the distance of the accelerated particle beam from the geometric center of the cavity increases.

[0065] The RF voltage can be tuned to maintain a high Q factor of the cavity during a frequency sweep by using, for example, a rotating capacitor / variable reactance element with intermeshing rotating and fixed blades. During each engagement of the blades caused by the rotation, the capacitance increases, thereby lowering the resonant frequency of the cavity. The blades can be shaped to produce the precise frequency sweep required. The drive motor for the rotating capacitor can be phase locked to the RF generator for precise control. In this example, during each engagement of the blades of the rotating capacitor, a beam of particles is accelerated.

[0066] Fig.13 An exemplary capacitive structure 1308 including a capacitive circuit is shown for controlling the shape of an RF voltage waveform applied to a dee plate 1000 (similar to dee plate 40) within the RF frequency range. Fig.13 For example, the capacitor structure 1308 can be configured and controlled to generate Figure 8 , Fig. 9 and Fig.10 , and variations and / or combinations thereof. The semicircular surfaces 1003, 1005 of the D-plate 1000 are connected to the inner conductor 1300 and housed in the outer conductor 1302, the semicircular surfaces 1003, 1005 defining a region 1007 of the cavity 19 where particles are accelerated. A high voltage is applied to the D-plate 1000 from a voltage source 1320 (e.g., an oscillating voltage input) through a power coupling device 1304, which electrically couples the voltage source to the inner conductor. In some embodiments, the coupling device 1304 is positioned on the inner conductor 1300 to provide power transfer from the voltage source to the D-plate 1000. In addition, the D-plate 1000 is coupled to variable reactance elements 1306, 1308 to enable RF frequency scanning and to change the RF frequency range and waveform shape in response to commands from a control system. For example, the variable reactance element 1306 can be configured and controlled to respectively change Figure 8 , 9The variable reactance element 1308 can be configured and controlled to change the maximum voltage and the minimum voltage of the RF voltage, for example, from Figure 8 and Fig. 9 Those changes shown in Fig.10 Those shown in .

[0067] The variable reactance element 1306 may include one or more rotating capacitors having a plurality of blades 1310 that may be rotated using a motor (not shown) controlled by a control system. By engaging or disengaging the blades 1310 at each cycle of the RF sweep, the capacitance of the RF structure changes, which in turn changes the resonant frequency (RF) of the cavity 19 and the frequency of the voltage applied to the cavity 19. In some embodiments, the blades 1310 engage with each other during each quarter cycle of the motor. 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 applied to the D-plate 1003 and to accelerate the beam can be reduced by a factor. In some embodiments, the shape of the blades 1310 is machined to achieve the dependence of the resonant frequency on time.

[0068] The blade rotation can be synchronized with the RF frequency generation.By varying the Q factor of the cavity 19 , the resonant frequency of the RF structure can be kept close to the frequency of the AC voltage potential applied to the dee plate 1003 .

[0069] The variable reactance element 1308 may be or include a capacitor formed by a plate 1312 and a surface 1316 of the inner conductor 1300. The plate 1312 may be movable in a direction 1314 toward 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 to be scanned in the cavity 19 (e.g., to change the minimum and / or maximum frequency), the distance D is set to a specific value. In order to change the frequency range scanned in the cavity 19, the plate 1312 may be moved corresponding to the change in the desired frequency range. The control system may use a motor (not shown) to control the movement of the plate 1312.

[0070] In some embodiments, the inner conductor 1300 and the outer conductor 1302 include a metallic material, such as copper, aluminum, or silver. The blades 1310 and the plate 1312 may also include the same or different metallic materials as the conductors 1300, 1302. The coupling device 1304 may be an electrical conductor. The variable reactance elements 1306, 1308 may have other forms and may be coupled to the D-plate 1000 in other ways to achieve RF frequency scanning and frequency range changes. In some implementations, a single variable reactance element may be configured to perform the functions of both variable reactance elements 1306, 1308. In some embodiments, more than two variable reactance elements may be used.

[0071] Figure 8 An example of the RF voltage frequency varying over time between a minimum 50 and a maximum 51 frequency is shown, which are examples of 90 MHz (megahertz) and 135 MHz, respectively. In a typical synchrocyclotron, the RF voltage waveform 55 remains constant 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 period and the injection period, respectively. For example, the acceleration period includes the time when the particles are accelerated within the cavity, and the injection period includes the time when the particles are injected into the cavity from the particle source, and includes the time when the particle source generates the pulse. The consistency can be defined in terms of pulse width 100, pulse height 101, or a combination thereof.

[0072] The particle source 25 is controllable to provide particles at a specific frequency approximately decreasing from a maximum RF frequency 51 to a minimum RF frequency 50 during a voltage frequency sweep. Figure 8 As shown, the particle source can be controlled to inject a pulse 56 composed of particles at any point between the starting frequency 57 and the ending frequency 58. The starting maximum frequency (125 MHz in this example) and the ending minimum frequency (124 MHz in this example) correspond to the frequency range in which the particles are most likely to be accepted by the synchrocyclotron. This frequency range is collectively referred to as the acceptance frequency in this article. At the acceptance frequency, given the magnetic and electric fields in the synchrocyclotron, the pulsed particles from the particle source have a high probability of acceleration. Acceptance includes cavity acceptance of particles and RF voltage acceleration of particles in the cavity. Considering the magnetic and electric fields in the synchrocyclotron, particles injected outside the acceptance frequency have a lower or low probability of acceptance. Therefore, the goal of particle injection during the acceptance frequency is to produce a larger beam current intensity. In other words, the more particles are accepted, the greater the particle density in the final beam. Figure 8 A particle pulse having a width spanning the entire acceptance frequency is shown in . Other example pulses may not extend across the entire acceptance frequency.

[0073] The current drawn from the particle accelerator is based on the amount of particles injected into the cavity and accepted by the cavity. In some examples, particles can only be successfully injected into the cavity within a few percent or less of the acceptance frequency. Therefore, the time that particles can be injected into the cavity and therefore the total beam current of the accelerator are limited by the slope of the frequency change as a function of time during the particle source pulse. For example, for a synchrocyclotron with a 1% frequency acceptance, an injection frequency of 124-125MHz, and an RF voltage frequency modulation (FM) rate of 0.075MHz / microsecond (μs), a particle source pulse 56 with a width of 17μs can be successfully injected into the synchrocyclotron. The duration of the pulse and the pulse repetition rate control the beam current that the synchrocyclotron can produce.

[0074] Thus, in some embodiments, the RF voltage during the injection period (i.e., when particles are injected into the cavity) can be varied so that its slope is less than the average slope of the RF voltage waveform during the acceleration period. In an example, the slope of the RF voltage waveform during the injection period can be less than the slope of the RF waveform at the same point along the waveform during the acceleration period. A slope that is 25% smaller when the particle source is injected can produce 25% more beam current compared to the average slope during the acceleration period. In other words, a slope that is less than one-quarter extends the duration of the acceptance frequency, which enables four times more particles to be injected during the extended acceptance frequency, resulting in four times more beam current. This lower frequency modulation slope can be controlled by the control system to rotate capacitor 1306 ( Fig.13 ) to provide the desired frequency distribution as a function of time. The shape of the blades can also be configured to affect the frequency.

[0075] exist Figure 1 In an example operation of a particle accelerator, Figure 8 RF voltage waveform 55 is the RF voltage supplied to cavity 19 during the acceleration period. Fig. 9 RF voltage waveform 60 is the RF voltage provided to cavity 19 during the implant 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 may be twice as large, three times as large, four times as large, etc. as the width of waveform 55. Thus, the slope 61 of waveform 60 at the acceptance frequency 124-125 MHz during particle implant 62 is less than the slope 61 of waveform 55 at the acceptance frequency 124-125 MHz during particle implant 65. Figure 8 ) has a slope of 64. Therefore, if pulse 69 ( Fig. 9 ) indicates that Fig. 9 The amount of particles that can be injected during the RF frequency sweep is greater than that during Figure 8 During the RF frequency scan (by Figure 856 in the pulse 56). That is, in both examples, the particles are injected between 125 MHz and 124 MHz; however, because the time period between 125 MHz and 124 MHz is longer in waveform 60 than in waveform 55, more particles can be injected using waveform 60. As a result, the beam current intensity is increased by using waveform 60 during the injection cycle. Waveform 55 can continue to be used during the acceleration cycle. The rotation capacitor 1306 / 1310 described herein can be controlled to switch between waveforms 55 and 60 at the appropriate time based on, for example, the pulse timing of the particle source. For example, when a potential is applied to the particle source cathode, the rotation capacitor described herein can be controlled to switch from waveform 55 to waveform 60.

[0076] In some embodiments, the decrease in the slope of the RF voltage waveform 55 to the RF voltage waveform 60 is proportional to the increase in the current in the particle beam. In some embodiments, the slope of the RF voltage waveform during the injection period is at least 75% less than the slope of the RF voltage waveform during the acceleration period. In some embodiments, the slope of the RF voltage waveform during the injection period is at least 50% less than the slope of the RF voltage waveform during the acceleration period. In some embodiments, the slope of the RF voltage waveform during the injection period is at least 30% less than the slope of the RF voltage waveform during the acceleration period. In some embodiments, the slope of the RF voltage waveform during the injection period is at least 25% less than the slope of the RF voltage waveform during the acceleration period. In some embodiments, the slope of the RF voltage waveform during the injection period is at least 20% less than the slope of the RF voltage waveform during the acceleration period. Generally, the slope of the RF voltage waveform during the injection period can be any appropriate percentage less than the slope of the RF voltage waveform during the acceleration period.

[0077] In some embodiments, a particle source timing trigger generated using one or more frequency comparators may be used. By using one or more frequency comparators (which may use a minimum frequency slope for reliable operation) and a timing delay, the particle source trigger may be initiated at any point in the RF voltage waveform, including at 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 the capacitor (e.g., 1308), an RF voltage waveform can be generated so 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 the rest of the waveform. For example, the acceptance frequency can start at the top of the waveform, or at 5% of the top of the downslope, at 10% of the top of the downslope, or at any suitable percentage of the top of the downslope. Fig.10In some embodiments, the amount of particles that can be extracted, as represented by pulse 72, is greater than the amount of particles at other locations of the waveform where the slope 74 is greater. As a result, the beam current is increased. In some embodiments, waveform 71 can be used during the implantation cycle and can be used during the acceleration cycle. Figure 8 In some embodiments, waveform 71 may be used during the implantation and acceleration periods. In some embodiments, the width 106 of waveform 71 may be increased like the width of waveform 60 (relative to the waveform used during the acceleration period), further increasing the duration of the acceptance frequency and the amount of particles that can be implanted at this time.

[0078] Fig.11 An example of an example comparator circuit 75 is shown, which can be used to identify the position at or near the top of the voltage waveform in order to identify the beginning or end of the acceptance frequency. Other types of frequency comparators can be used to perform this function. In this example, a single RF voltage value (e.g., from Fig.10 The waveform 71 of the RF voltage waveform is sampled and digitized to produce a first pulse train with a frequency F1, which can be compared with a reference pulse train with 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 the flip-flops 76 and 77 (signals Q1 and Q2, respectively) are applied to the NAND gate 78. The NAND gate 78 outputs a control of whether to reset the flip-flops 76 and 77. The signals Q1 and Q2 are provided to a low-pass filter 79 including a capacitor and two resistors, and their resulting filtered values ​​are compared by an analog comparator 80. Based on the comparison performed using the signals Q1 and Q2, the output of the frequency comparator 75 can determine a predefined point along the RF voltage waveform, such as the top or near the top. That is, the frequency at which Q1 exceeds Q2 corresponds to a position at or near the top of the RF voltage waveform.

[0079] Return to reference Figure 1As described above, the magnetic field in cavity 19 is shaped to cause the particles to move along the orbit within the cavity. Exemplary synchrocyclotrons employ a magnetic field whose rotation angle is uniform and whose strength decreases with increasing radius. In some embodiments, the maximum magnetic field generated by the superconducting (main) coils may be in the range of 2.5T to 20T at the center of the cavity, with the magnetic field decreasing with increasing radius. For example, the superconducting coils may be used to generate magnetic fields equal to or exceeding one or more of 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, 6T, 6.7T, 6.8T, 6.9T, 7.0T, 7.1T, 7.2T, 7.3T, 7.4T, 7.5T, 7.6T, 7.7T, 7.8T, 7.9T, 8.0T, 8.1T, 8.2T, 8.3T, 8.4T, 8.5T, 8.6T, 8.7T, 8 .8T, 8.9T, 9.0T, 9.1T, 9.2T, 9.3T, 9.4T, 9.5T, 9.6T, 9.7T, 9.8T, 9.9T, 10.0T, 10.1T, 10.2T, 10.3T, 10.4T, 10.5T, 10.6T, 10.7T, 10. 8T, 10.9T, 11.0T, 11.1T, 11.2T, 11.3T, 11.4T, 11.5T, 11.6T, 11.7T, 11.8T, 11.9T, 12.0T, 12.1T, 12.2T, 12.3T, 12.4T, 12.5T, 12.6 T, 12.7T, 12.8T, 12.9T, 13.0T, 13.1T, 13.2T, 13.3T, 13.4T, 13.5T, 13.6T, 13.7T, 13.8T, 13.9T, 14.0T, 14.1T, 14.2T, 14.3T, 14.4T, 14.5T, 14.6T, 14.7T, 14.8T, 14.9T, 15.0T, 15.1T, 15.2T, 15.3T, 15.4T, 15.5T, 15.6T, 15.7T, 15.8T, 15.9T, 16.0T, 16.1T, 16.2T, 1 6.3T, 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. In addition, the superconducting coil can be used to generate a magnetic field outside the range of 2.5T to 20T or in the range of 3T to 20T but not specifically listed herein. .

[0080] By generating a strong magnetic field having a size as described above, the bending radius of particles traveling within the cavity 19 can be reduced. Due to the reduction in the bending radius, a greater number of particle tracks can be generated within a cavity of a given size. Therefore, a greater number of tracks can be installed in a smaller cavity. Reducing the size of the cavity generally reduces the size of the particle accelerator because a smaller cavity requires a smaller yoke or pole piece and other components. In some embodiments, the size or volume of the particle accelerator can be 4m 3 (cubic meters) or less, 3m 3 or smaller, or 2m 3 or smaller.

[0081] The particles travel from the particle source through a generally spiral orbit. In half of each loop of the spiral path, the protons gain energy as they pass through the RF electric field in space 43. As the particles gain energy, the center orbit radius of each successive loop of their spiral path becomes larger than the previous loop, until the loop radius reaches the maximum radius of the polar face. At this point, the magnetic and electric field disturbances direct the particles to an area where the magnetic field rapidly weakens, and the particles leave the high magnetic field area and are directed through a vacuum tube 46 ( Figure 2 and Figure 3 ) (herein referred to as the extraction channel) to leave the yoke of the particle accelerator. A magnetic regenerator can be used to change the magnetic field disturbance to guide the particles. When the particles leaving the particle accelerator enter the area where the magnetic field in the space surrounding the particle accelerator is significantly weakened, they will tend to disperse. The beam shaping elements 48, 49 in the extraction channel 46 redirect the particle accelerator so that they stay in a straight beam with a limited spatial range.

[0082] When the beam leaves the extraction channel, it passes through the beam forming system, an example of which is shown below. Figure 6 As described, the beam forming system can be programmably controlled to create a desired combination of scanning, scattering and / or range modulation of the output particle beam.

[0083] Ultra-high dose rate FLASH therapy may require higher average and instantaneous beam current intensities than non-FLASH applications. These higher average and instantaneous beam current intensities can be achieved using the technology described herein. The particle accelerator, treatment system and variants thereof described herein can be configured and controlled to apply ultra-high dose rate radiation (e.g., FLASH dose rate) to an irradiation target in a patient's body. In this regard, experimental results of radiotherapy have shown that when a therapeutic dose is delivered at an ultra-high (FLASH) dose rate, the condition of healthy tissues subjected to radiation is improved. In one example, when a radiation dose of 10 to 20 grays (Gy) is delivered in a pulse of less than 500 milliseconds (ms), reaching an effective dose rate of 20 to 100 grays per second (Gy / S), healthy tissues experience less damage than when irradiated with the same dose over a longer time scale, and tumors are treated with similar effectiveness. The theory that can explain this "FLASH effect" is based on the fact that radiation damage to tissues is proportional to the oxygen supply in the tissues. In healthy tissue, ultra-high dose rates radicalize oxygen only once, as opposed to dosing that radicalizes oxygen multiple times over a longer time scale. Using ultra-high dose rates, this can result in less damage to healthy tissue.

[0084] In some examples, as described above, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gy per second for a duration less than 500 ms. In some examples, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gy per second for a duration between 10 ms and 5 s. In some examples, ultra-high dose rate radiation can include a radiation dose exceeding 1 Gy per second for a duration less than 5 s.

[0085] In some examples, ultra-high dose rate radiation includes a radiation dose exceeding one of the following doses in 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 radiation dose exceeding one of the following doses: 2 Gray per second, 3 Gray per second, 4 Gray per second, 5 Gray per second, 6 Gray per second, 7 Gray per second, 8 Gray per second, 9 Gray per second, 10 Gray per second, 11 Gray per second, 12 Gray per second, 13 Gray per second, 14 Gray per second, 15 Gray per second, 16 Gray per second, 17 Gray per second, 18 Gray per second, 19 Gray per second, 20 Gray per second, 30 Gray per second, 40 Gray per second, 50 Gray per second, 60 Gray per second, 70 Gray per second, 80 Gray per second, 90 Gray per second, or 100 Gray per second over a duration between 10 ms and 5 s. In some examples, ultra-high dose rate radiation includes a radiation dose exceeding one of the following doses in a duration of less than 5 seconds: 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.

[0086] In some examples, ultra-high dose rate radiation includes a radiation dose exceeding one or more of the following doses: 100 Gray per second, 200 Gray per second, 300 Gray per second, 400 Gray per second, or 500 Gray per second in a duration of less than 500 ms, in a duration between 10 ms and 5 s, or in a duration of less than 5 s.

[0087] In some examples, the ultra-high dose rate of radiation includes a radiation dose between 20 Gray per second and 100 Gray per second within a duration of less than 500 ms. In some examples, the ultra-high dose rate of radiation includes a radiation dose between 20 Gray per second and 100 Gray per second within a duration between 10 ms and 5 s. In some examples, the ultra-high dose rate of radiation includes a radiation dose between 20 Gray per second and 100 Gray per second within a duration of less than 5 s. In some examples, the ultra-high dose rate of radiation includes a radiation dose between 40 Gray per second and 120 Gray per second within a time period such as less than 5 s. Other examples of time periods are those provided above.

[0088] refer to Figure 6 , an example particle therapy system 82 using the accelerator and techniques described herein includes a gantry 84. The gantry 84 includes an annular or circular support structure 85 and a beamline structure 86. The combination of the support structure 85 and the beamline structure 86 can be referred to as a "compact gantry" due to its relatively small size. The beamline structure 86 includes an output channel 87 mounted to the support structure 85 and a channel 88 that guides the 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 may include a system isocenter, where a patient may be positioned for treatment. In an example, the motor may move the output channel 87 along a track on the structure 85, causing the output channel 87 to rotate relative to the treatment position 89. In an example, the structure to which the output channel 87 is attached may rotate relative to the treatment position 89 at the treatment couch 89a, causing the output channel 87 to rotate relative to the treatment position. In some embodiments, the rotation achieved 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 be rotated 360°, and therefore, the output channel 87 can be positioned at 0°, 90°, 270°, and back to 0° / 360° or any angle in these rotational positions. As previously described, the beam line structure 86 is configured to guide the particle beam from the accelerator 10 to the treatment position 89. To this end, the output channel 87 includes a magnetic element to bend the particle beam toward the treatment position. In addition, the beam line structure 86 includes a channel 88, which includes a magnetic element along the beam line, and the magnetic element guides the particle beam from the particle accelerator 10 to the output channel 87.

[0089] The output channel includes a dipole magnet arranged in series to bend the particle beam by at least 90°. The dipole magnet may include at least a first dipole magnet and a second dipole magnet. The magnets in the output channel may be configured to bend the particle beam by at least 90° toward the irradiation target in the presence of a magnetic field of at least 3 Tesla (T). In some examples, the output channel includes a magnetic element to bend the particle beam toward the irradiation target by more than 90°, such as 100°, 110°, 120° or more.

[0090] A beam shaping system may be included in the treatment head 90, which may include one or more scanning magnets, a range shifter consisting of a plurality of plates that can be moved in and out of the particle beam path, and a configurable collimator. In some embodiments, one or more scanning magnets may be included in the beam line structure 86 and / or the output channel 87.

[0091] like Figure 7 As shown, another example particle therapy system 120 using the accelerator and technology described herein includes a gantry. The gantry 94 can be connected to the treatment room floor 96 rotationally or axially so that the gantry 94 can be controlled to move relative to the treatment room floor. In this example, the particle accelerator 10 is mounted on the gantry and can rotate around the patient with the gantry to guide the particle beam in the direction of arrow 121. The gantry 94 can include an arm 97 that extends along the length of the gantry 94 and reaches the treatment room floor 96. The particle accelerator 10 and the connected beam line structure 98 are rotatably mounted on the arm 97. That is, the particle accelerator 10 and the connected beam line structure 98 are connected to the end 99 of the arm 97 so that the particle accelerator 10 and the connected beam line structure 98 can rotate in the direction of arrow 122 at the end 99. This rotation is separate from the gantry rotation described herein. The beam line structure can contain magnetic elements to bend the particle beam for use in applications close to the patent. For example, the beam line structure may include magnetic elements to bend the particle beam toward the irradiation target by more than 90°, such as 100°, 110°, 120° or more.

[0092] Fig.12A portion of an example of a proton therapy system 104 is shown that includes a particle accelerator mounted on a gantry that uses the accelerators and techniques described herein. Because the accelerator is mounted on a gantry, the particle accelerator is within or adjacent to the treatment room. In some embodiments, the gantry is steel and has two legs (not shown) that are mounted for rotation on two corresponding tracks located on opposite sides of the patient. The gantry can include a steel truss (not shown) connected to each leg of the gantry, the steel truss being long enough to span the treatment area in which the patient lies, and the ends of the steel truss being attached to the rotating legs of the gantry. The particle accelerator can be supported by the steel truss for movement around the patient. Fig.12 In the example of FIG. 1 , a patient is mounted on a treatment couch 105. The treatment couch 105 includes a platform that supports the patient.

[0093] The control system 92 ( Figure 6 and Figure 7 ) at least partially controls the operation of the example particle accelerator and particle therapy system described herein and the operation of all or some of its components, the control system 92 being configured to execute one or more computer program products, such as one or more computer programs tangibly embodied in one or more non-transitory machine-readable media, for execution or control of its operation by one or more data processing devices (e.g., programmable processors, computers, multiple computers and / or programmable logic components).

[0094] All or part of the systems described in this specification and various modifications thereof may be configured or controlled at least in part by one or more computers, such as a control system using one or more computer programs tangibly embodied in one or more information carriers, such as one or more non-transitory machine-readable storage media. The computer program may be written in any form of programming language, including compiled or interpreted languages, and it may be deployed in any form, including as a stand-alone program or as a module, part, subroutine, or other unit suitable for use in a computing environment. The computer program may be deployed to execute on one computer, or on multiple computers at one location, or distributed across multiple locations and interconnected by a network.

[0095] The actions associated with configuring or controlling the systems described herein may be performed by one or more programmable processors executing one or more computer programs to control or perform all or some of the operations described herein. All or part of the systems and processes may be configured or controlled by dedicated logic circuitry, such as an FPGA (field programmable gate array) and / or an ASIC (application specific integrated circuit) or an embedded microprocessor limited to instrument hardware.

[0096] For example, processors suitable for executing computer programs include, for example, general-purpose microprocessors and special-purpose microprocessors, and any one or more processors of any kind of digital computer. Typically, the processor will receive instructions and data from a read-only storage area or a random access storage area or both. The elements of a computer include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Typically, a computer will also include one or more machine-readable storage media, or be operatively coupled to one or more machine-readable storage media to receive data from one or more machine-readable storage media, or to transfer data to one or more machine-readable storage media, or both, the machine-readable storage medium is, for example, a mass storage device for storing data, such as a magnetic disk, a magneto-optical disk, or an optical disk. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage areas, including, for 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-ROMs (compact disk read-only memory) and DVD-ROMs (digital versatile disk read-only memory).

[0097] The elements of the different embodiments described can be combined to form other embodiments not previously specifically described. Elements can be excluded from the previously described system without adversely affecting their operation or the operation of the system as a whole. In addition, various individual elements can be combined into one or more individual elements to perform the functions described in this specification.

[0098] In the description and claims provided herein, unless the context indicates otherwise, the adjectives "first", "second", "third", etc. do not necessarily specify priority or order. Instead, these adjectives may be used merely to distinguish the nouns they modify.

[0099] Any mechanical or electrical connections herein may include a direct physical connection or an indirect physical connection involving one or more intermediate components. The electrical connections may be wired and / or wireless.

[0100] Other implementations not specifically described in this specification are also within the scope of the appended claims.

Claims

1. A particle accelerator, comprising: a particle source, used for providing particles to the magnetic cavity; circuitry that provides a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from an ionized plasma on track in the magnetic cavity, the slope of the RF voltage being less when the particles are injected into the magnetic cavity than when the particles are accelerated in the magnetic cavity; and The extraction channel is used to receive particles from the magnetic cavity to be output from the particle accelerator as a particle beam.

2. The particle accelerator according to claim 1, wherein: The RF voltage has a first slope when the particles are injected into the magnetic cavity and has a second slope when the particles are accelerated in the magnetic cavity, the first slope being smaller than the second slope at least during a decrease in the RF voltage.

3. The particle accelerator according to claim 2, wherein: The first slope is at least 50% less than the second slope.

4. The particle accelerator according to claim 2, wherein: The first slope is at least 30% less than the second slope.

5. The particle accelerator according to claim 2, wherein: The first slope is at least 20% less than the second slope.

6. The particle accelerator according to claim 1, wherein: The smaller slope corresponds to an increase in current in the particle beam when the particles are injected into the magnet cavity.

7. The particle accelerator according to claim 1, wherein: The smaller slope is proportional to the increase in current in the particle beam as the particles are provided to the magnetic cavity.

8. The particle accelerator of claim 1, further comprising: An RF controller includes a rotation capacitor to vary the RF voltage, the rotation capacitor including a plate having a shape that is reduced based on a target RF voltage slope.

9. The particle accelerator system according to claim 1, wherein: The particle beam is delivered at a FLASH dose rate.

10. The particle accelerator according to claim 1, wherein: The particle beam is delivered at a dose in excess of twenty (20) grays per second for a duration of less than five (5) seconds.

11. A particle therapy system, comprising: The particle accelerator according to claim 1; and A gantry is configured to enable output of a particle beam to a patient.

12. The particle therapy system according to claim 11, wherein: The gantry comprises a channel for conveying the particle beam, the channel comprising a dipole magnet configured to bend the particle beam by at least 90° toward the patient, the dipole magnet being mounted to rotate about the gantry.

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

14. A system comprising: a particle source, the particle source providing particles to the magnetic cavity; circuitry that provides a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from an ionized plasma on track in the magnetic cavity; a control system for controlling the particle source to provide particles to the magnetic cavity based on the slope of the RF voltage; and The extraction channel is used to receive particles from the magnetic cavity to be output from the particle accelerator as a particle beam.

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

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

17. The system of claim 14, wherein: The control system is configured to control the particle source to provide particles to the magnetic cavity during an RF voltage having a first waveform generated for an injection period, the first waveform having an increased waveform width relative to a second waveform generated for an acceleration period.

18. The system of claim 14, wherein: The control system is configured to control the particle source to provide the particles to the magnetic cavity at or near a top of a waveform generated for an injection cycle; and Wherein, the waveform generated for the injection period has an increased waveform width relative to the waveform generated for the acceleration period.

19. The system of claim 14, wherein: The particle beam is delivered at a FLASH dose rate.

20. The system of claim 14, wherein: The particle beam is delivered at a dose in excess of twenty (20) grays per second for a duration of less than five (5) seconds.

21. The system of claim 14, further comprising: A gantry is configured to output the particle beam to a patient.

22. The system of claim 16, wherein: The gantry comprises a channel for conveying the particle beam, the channel comprising a dipole magnet configured to bend the particle beam by at least 90° toward the patient, the dipole magnet being mounted to rotate about the gantry.

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

24. A particle source comprising: a tube for introducing a 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 an electrical potential to ionize the gas to produce the particles; and A valve is controllable to allow or prevent gas from reaching the opening.

25. The particle source according to claim 24, wherein The valve is located within the tube and closer to the opening than to either electrode.

26. The particle source of claim 24, wherein The valve comprises a piezoelectric displacement valve.

27. The particle source of claim 24, wherein: The pressure of the gas in the tube is 10 -4 Torr (0.0133322 Pascal (Pa)) or greater.

28. The particle source of claim 24, wherein: Ionizing the gas generates a plasma in the tube, the plasma having at least a predetermined particle density.

29. The particle source according to claim 28, wherein The predetermined particle density is 10 15 ions / cm 3 .

30. The particle source of claim 24, wherein: The valve is 3 cm or less from the opening.

31. The particle source of claim 24, wherein: The valve is 2 cm or less from the opening.

32. The particle source of claim 24, wherein: The valve is 1 cm to 4 cm away from the opening.

33. The particle source of claim 24, wherein: The electrodes include a cathode that is periodically charged, thereby generating electrical pulses that ionize the gas to create a plasma and release the particles into the region.

34. The particle source of claim 33, wherein Electrical pulses are generated once every millisecond or more, with durations on the order of single-digit microseconds.

35. The particle source of claim 24, wherein: The tubes are completely separated in this area.

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

37. A system comprising: a particle source, the particle source providing particles to the magnetic cavity; circuitry for providing a radio frequency (RF) voltage to the magnetic cavity to accelerate the particles on track in the magnetic cavity; and a control system for controlling the particle source to provide particles to the magnetic cavity; The particle source comprises: 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 released into the region; electrodes on different sides of the opening for applying an electrical potential to ionize the gas to produce the particles; and A valve is controllable to allow or prevent gas from reaching the opening.

38. The system of claim 38, wherein: The gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to reduce the effect of the first pressure in the tube on the second pressure in the magnetic cavity.

39. The system of claim 38, wherein: The gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to prevent the gas from reaching the opening during a period when a potential is not applied to the electrode.

40. The system of claim 38, wherein: The electrodes include a cathode that is periodically charged to generate electrical pulses that ionize the gas to generate plasma and release the particles into the region; and wherein the gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to prevent the gas from reaching the opening during at least part of the time when the electrical pulse is not generated.

41. The system of claim 38, wherein: The gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to allow the gas to reach the opening when an electrical potential is applied to the electrode.

42. The system of claim 38, wherein: The gas in the tube is at a first pressure, the magnetic cavity is at a second pressure 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 before the potential is applied to the electrode.

43. The system of claim 38, wherein: The electrodes include a cathode that is periodically charged to generate electrical pulses that ionize the gas to generate plasma and release the particles into the region; and wherein the gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to allow the gas to reach the opening during the generation of the electrical pulse.

44. The system of claim 38, wherein: The electrodes include a cathode that is periodically charged to generate electrical pulses that ionize the gas to generate plasma and release the particles into the region; and wherein the gas in the tube is at a first pressure, the magnetic cavity is at a second pressure less than the first pressure, and the valve is controllable to allow gas to reach the opening only during the time when the electrical pulse is generated and only for a predetermined duration before the electrical pulse is generated.

45. The particle source of claim 38, wherein: The valve is located in the tube and is closer to the opening than either electrode.

46. ​​The particle source of claim 38, wherein The valve comprises a piezoelectric displacement valve.

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