High frequency source with phase stabilization element

Abstract

The invention relates to a high-frequency source for a linear accelerator system, the linear accelerator system, a method for operating a high-frequency source and an associated computer program product.The high-frequency source according to the invention for a linear accelerator system comprises: a microwave generator for generating microwaves, a control unit, and a circulator, which has ferrites for isolating the microwave generator against backscattered microwaves by influencing the phase of the microwaves as a function of a magnetic field, characterized in that the circulator has an electrical phase stabilization element, wherein the control unit is configured for receiving a measured quantity describing a magnetic permeability of the circulator and for adjusting a current and / or voltage of the electrical phase stabilization element to influence the magnetic field as a function of the received measured quantity, such that the amplitude difference between the generated microwaves and the backscattered microwaves is maximized.

Description

[0001] The invention relates to a high-frequency source for a linear accelerator system, the linear accelerator system, a method for operating a high-frequency source and an associated computer program product.

[0002] High-frequency sources are regularly used to provide high-frequency microwaves, which are used, for example, to accelerate charged particles, especially electrons, in a conventional linear accelerator system. Such a high-frequency source for a linear accelerator is known, for example, from DE 10 2012 209 185 A1.

[0003] Peng Chengyao et al. reveal in "Design of temperature compensating unit for the circulator in 6 MW 4.6 GHz LHCD system", November 15, 2016, XP055938067, that the Lower Hybrid Current Drive (LHCD) system is a crucial component of the Experimental Advanced Superconducting Tokamak (EAST). As the primary RF power amplifier, the klystron in the LHCD system is protected by a high-power circulator. Under high-power conditions, the temperature of the ferrites in the circulator drifts, which can impair the microwave power output of the circulator and even damage the klystron. Therefore, this publication presents and implements a temperature compensation unit (TCU) design to compensate for the high-power-induced temperature drift. Experiments demonstrate that the TCU enables continuous high-power operation of the circulator.

[0004] From Kim Jeehyun et al., "Test and operation of high-power RF system for KSTAR helicon current drive system," April 9, 2021, XP086540274, it is known that the KSTAR helicon current drive system for efficient off-axis current propulsion is currently being upgraded with 476 MHz, 1.2 MW klystrons and a new high-voltage power supply (HVPS). Four klystrons were used. Each klystron can generate 1.2 MW of CW RF power at 476 MHz with an 84 kV 24 A beam. Two klystrons are operated in parallel with a single pulse-step modulator HVPS operating at 92 kV and 64 A.

[0005] US 5,291,290 A describes a high-power RF transmission system for electrical signals, for example, a television transmission system operating in the 100 kW range in a UHF band, comprising one or more high-power klystrons whose outputs are combined and fed to the first, connection of a high-power Y-connected ferrite circulator with three terminals, the second terminal of the circulator feeding the transmitting antenna system of the broadcasting system, the third terminal of the circulator feeding a non-reflective RF load, and means for tuning the circulator to compensate for temperature changes in the ferrite material of the circulator, so that the klystron(s) are isolated from reflections from the antenna system. Due to the special requirements of HDTV broadcasting, as described in more detail herein, the invention is particularly applicable to a high-power HDTV broadcasting system.

[0006] From US 3,714,592 A, a resonant microwave load, such as a microwave linear accelerator section, is known which is coupled to a magnetron oscillator via a circulator. Power reflected from the resonant load is reflected to the circulator and from there to a wave-absorbing load. A composite wave reflector and variable phase shifter is provided between the absorbing load and the circulator to reflect a portion of the power reflected from the resonant load to the magnetron oscillator in order to pull the oscillator's frequency to the frequency of the resonant load. The composite wave reflector and variable phase shifter includes a wave-reflecting element supported by a support rod that passes through the wall of a rectangular waveguide.The rotation of the support rod causes the wave-reflecting element to move in a generally axial direction within the waveguide in order to adjust the phase of the reflected wave so that the frequency of the magnetron is pulled to the frequency of the resonant load.

[0007] Depending on the application, the linear accelerator system provides high-energy charged particles or MeV photons, particularly MeV X-rays, the latter typically generated by the interaction of the charged particles with a target within the linear accelerator unit. The linear accelerator system is used, for example, in customs inspections and / or materials testing. Its use in radiation therapy and / or medical imaging is also conceivable and known.

[0008] Such a linear accelerator system typically comprises two of the three main components that conventionally work together in a system. The first main component is the linear accelerator unit. Another main component is a power supply module, which is designed to provide and / or control and / or regulate the electrical voltages and / or currents required by the (other) main components and includes, for example, the high-frequency source. A third main component is a cooling system, for example, called a "chiller."

[0009] The cooling system typically serves to stabilize the temperature of the high-frequency source, particularly its circulator. Temperature stabilization specifically means temperature control. The cooling system is, in particular, a temperature control system. The cooling system provides cooling or heating power for temperature stabilization. Temperature stabilization specifically includes temperature control, i.e., cooling and / or heating. Without temperature stabilization, a temperature change typically leads to an additional phase shift in the circulator's ferrites. This additional phase shift typically has a detrimental effect on the degree of isolation of the microwave generator against backscattered microwaves. Effective isolation typically requires a specific phase relationship between the generated microwaves and the backscattered microwaves.

[0010] A conventional cooling system of this type typically requires approximately one-third to one-half of the installation space and one-third to one-half of the system's electrical power consumption. This need for installation space and / or electrical power increases the overall demands placed on the environment housing the system. Operating a conventional system is therefore quite challenging, especially when the system is mounted on a mobile platform. This mobile platform could, for example, be part of a truck.

[0011] If the environment housing the system cannot fully meet the requirements, the system can typically only be operated at reduced beam performance. This reduced beam performance allows for a reduction in the cooling capacity of the cooling system, thereby lowering the required installation space and / or electrical power. Alternatively or additionally, the system, particularly the cooling system, can be conventionally scaled down by sharing some of its cooling capacity with another existing cooling system. However, the latter requires a comparatively high degree of system integration and / or connection to other systems, which usually increases the system's complexity.

[0012] The invention is based on the objective of providing a high-frequency source for a linear accelerator system, the linear accelerator system, a method for operating a high-frequency source and an associated computer program product with an increased temperature operating range.

[0013] The problem is solved by the features of the independent claims. Advantageous embodiments are described in the dependent claims.

[0014] A high-frequency source according to the invention for a linear accelerator system has a microwave generator for generating microwaves, a control unit, a circulator which has ferrites for isolating the microwave generator against backscattered microwaves by influencing the phase of the microwaves as a function of a magnetic field, wherein the circulator has an electrical phase stabilization element, wherein the control unit is configured for receiving a measurement quantity describing a magnetic permeability of the circulator and for adjusting a current and / or voltage of the electrical phase stabilization element to influence the magnetic field as a function of the received measurement quantity, wherein an amplitude difference between the generated microwaves and the backscattered microwaves is maximized, and a measuring device for measuring an electromagnetic quantity of the backscattered microwaves. characterized by that the electromagnetic quantity is the measured quantity describing the magnetic permeability of the circulator, where the electromagnetic quantity describes an amplitude and / or a phase of the backscattered microwaves.

[0015] A method according to the invention for operating the high-frequency source comprises the following steps: Receiving the measured quantity describing the magnetic permeability of the circulator in the control unit, adjusting the current and / or voltage of the electrical phase stabilization element to influence the magnetic field depending on the measured quantity by means of the control unit such that the amplitude difference of the generated microwaves and the backscattered microwaves is maximized.

[0016] The method for operating the high-frequency source essentially comprises controlling or regulating the high-frequency source.

[0017] An advantage of the high-frequency source, or of operating the high-frequency source in this manner, is that the high-frequency source according to the invention advantageously requires significantly less installation space and / or electrical power compared to a conventional high-frequency source. This advantage is realized, for example, by the fact that the electrical phase stabilization element in the high-frequency source actively counteracts temperature fluctuations, which in particular cause changes in the magnetic permeability and thus, in particular, in the phase relationship of the microwaves.

[0018] The high-frequency source preferably compensates for a partial or complete loss of cooling power, which can typically be used for temperature stabilization of the high-frequency source, by actively controlling the electrical phase stabilization element. The compensation particularly includes electrothermal and / or electromagnetic compensation.

[0019] The microwave generator comprises, in particular, a magnetron or a klystron. A high voltage is typically applied to an input of the microwave generator, which is converted at the output side into high-frequency microwaves with a high-frequency power that depends on the high voltage. The microwave generator produces, in particular, an alternating electromagnetic field in the GHz range, especially between 1 and 10 GHz, preferably between 2 and 4 GHz, in the form of microwaves. The generated microwaves are particularly suitable for accelerating charged particles.

[0020] The generated microwaves are defined as those microwaves produced by the microwave generator. The generated microwaves are, in particular, forward-directed microwaves. Backscattered microwaves are, in particular, backward-directed microwaves. The backscattered microwaves are, in particular, those microwaves that are backscattered by a payload of the circulator, for example, by the linear accelerator system, and / or by the circulator itself, especially depending on the generated microwaves.

[0021] The circulator has, in particular, at least three ports, wherein the first port is connectable to the microwave generator, the second port is connectable to a payload, in particular a linear accelerator unit of the linear accelerator system, and the third port is connectable to a load, in particular for the absorption of backscattered microwaves. Such a three-port circulator typically has a Y-shape, with the legs offset by 120°. It is also conceivable that the circulator has a fourth port, which, for example, is connectable to a reflection phase shifter or another load. In operation, the circulator is typically connected to the respective port, for example, via a waveguide. The load and / or the additional load can, in particular, be a water load.

[0022] The circulator is a ferritic circulator. The circulator incorporates ferrites arranged and configured to separate the generated microwaves from the backscattered microwaves and / or prevent the backscattered microwaves from being fed back to the microwave generator. To magnetize the ferrites, the circulator typically includes an additional permanent magnet. The ferrites can act as insulators, particularly because they are exposed to a magnetic field.

[0023] The frequency range of the microwaves to be separated in the circulator is advantageously adjustable by means of the control unit. The circulator is advantageously a substantially temperature-independent circulator due to the electrical phase stabilization element. The circulator of the high-frequency source preferably has a larger operating temperature range than a conventional circulator because the electrical phase stabilization element can compensate for temperature fluctuations. The operating temperature range of the circulator is in particular at least ±2°C, preferably at least ±5°C, advantageously at least ±20°C, and most advantageously at least ±50°C. The preferred operating temperature of the circulator is, for example, 30°C, 40°C, 60°C, or 80°C and lies within the respective operating temperature range. The operating temperature range of ±°C refers, for example, to the operating temperature and not necessarily to 0°C.Within the operating temperature range, the high-frequency source, in particular the circulator, can be operated optimally, preferably with sufficient efficiency. Within the operating temperature range, i.e., from a lower limit to an upper limit, the microwaves passing through the circulator preferably have essentially the same phase due to regulation by means of the electrical phase stabilization element.

[0024] The control unit can be, in particular, a computing unit or form part of a computing unit. The control unit has, in particular, an input interface for receiving the measured quantity. The measured quantity represents a value of the magnetic permeability. The measured quantity can be vector-based. The measured quantity can, in particular, be time-resolved. The control unit can, in particular, be configured to initiate or trigger the measurement with the measuring device. The control unit can trigger the measurement multiple times. The measurement can be performed in a clocked and / or continuous manner.

[0025] The control unit can be part of a measuring device or connected to the measuring device via cable or wirelessly. The control unit can receive the measured value, in particular via the input interface, store it in a buffer unit, and / or process it during adjustment. This processing is carried out according to logic and / or an algorithm. The processing can be carried out using program code that implements the logic and / or algorithm. The processing can be digital and / or analog. The processing can be repeated. When adjusting the current and / or voltage of the electrical phase stabilization element, the measured value is processed, for example, after it is received and / or stored in the buffer unit.

[0026] Setting the current and / or voltage includes, in particular, processing the measured value and / or determining a control value. The determined control value can be applied to an output interface of the control unit. Alternatively or additionally, the control unit can be configured to apply the current and / or voltage to the electrical phase stabilization element using the determined control value.

[0027] The current and / or voltage is adjusted, for example, multiple times, preferably in a clocked and / or continuous manner, particularly according to the logic and / or algorithm. Adjustment specifically involves solving an optimization problem with the aim of maximizing the amplitude difference and / or minimizing the radio frequency power of the backscattered microwaves. The logic and / or algorithm are specifically designed to maximize the amplitude difference. In other words, adjustment can be performed multiple times until the amplitude difference is maximized. Adjustment may result in a decrease in the amplitude difference compared to the previous adjustment. Advantageously, the control unit corrects the decreasing amplitude difference by means of a subsequent adjustment.

[0028] The fact that the amplitude difference is at its maximum means, in particular, that the circulator is capable of isolating the high-frequency source during operation. In other words, the electrical phase stabilization element ensures the circulator's insulating capability during operation. The circulator's insulating capability depends, in particular, on the magnetic field applied to the ferrites and the temperature of the ferrites.

[0029] The fact that the amplitude difference is maximal means, in particular, that the high-frequency power transmitted by the generated microwaves is significantly greater than the high-frequency power transmitted by the backscattered microwaves. Advantageously, the insertion loss is less than 1 dB. In particular, the back-direction attenuation is greater than 20 dB, preferably greater than 30 dB. The fact that the amplitude difference is maximal typically means that the high-frequency power of the backscattered microwaves is minimal.

[0030] The magnitude of the maximum amplitude difference can vary, particularly depending on the time of measurement. For example, the radio frequency source provides radio frequency power in the form of microwaves with a specific pulse length, defined over time. At the beginning of the pulse, the radio frequency power of the backscattered microwaves is typically greater than the radio frequency power of the backscattered microwaves in steady state.

[0031] Adjusting the current and / or voltage specifically involves controlling the electrical phase stabilization element. This adjustment ensures that the measured quantity influences the magnetic field via the electrical phase stabilization element. Specifically, it allows for the compensation of unwanted permeability deviations and, consequently, magnetic field deviations. The set current and / or voltage directly influence the magnetic field at the ferrites in the circulator. The electrical phase stabilization element may have an input interface for receiving the control value.

[0032] The electrical phase stabilization element is a component of the circulator. The electrical phase stabilization element consumes electrical power depending on the set current and / or voltage. The electrical phase stabilization element is in direct physical contact with the circulator. It is rigidly connected and / or coupled to the circulator. Depending on the set current and / or voltage, the electrical phase stabilization element exerts an effect, particularly in the immediate vicinity of the circulator and / or on or to the ferrites. The electrical phase stabilization element influences the magnetic field, for example, by superimposing its magnetic field with another magnetic field and / or by affecting the permeability of the ferrites.The manipulation of the magnetic field includes, in particular, changing the magnitude and / or direction of the magnetic field.

[0033] One embodiment provides that the electrical phase stabilization element for influencing the magnetic field comprises a controllable inductive component through which the set current and / or voltage flows. In this embodiment, the magnetic field provided by the ferrites is superimposed with the additional magnetic field of the inductive component. This embodiment is particularly advantageous because the magnetic field is controlled directly, which can typically be done relatively quickly.

[0034] One embodiment provides that the inductive component has at least one electromagnetic coil. Advantageously, the at least one electromagnetic coil allows for precise control of the magnetic field by applying the set current and / or voltage. The at least one electromagnetic coil is, for example, located at one of the ferrites. Additionally, another electromagnetic coil can be located at a different ferrite. The arrangement of the ferrites and the at least one electromagnetic coil is typically symmetrical. The coil is made of copper, for example.

[0035] One embodiment provides that the electrical phase stabilization element additionally comprises a permanent magnet around which at least one electromagnetic coil is wound. Alternatively, the electromagnetic coil can be wound around the second permanent magnet. The at least one electromagnetic coil and the permanent magnet or the second permanent magnet form a particularly advantageous controllable magnet for influencing the magnetic field. To close a magnetic circuit, a U-shaped yoke can be arranged around the at least one electromagnetic coil and around the permanent magnet or the second permanent magnet.

[0036] One embodiment provides that the electrical phase stabilization element for influencing the magnetic field includes a controllable electrothermal component through which the set current and / or voltage flows, thus regulating the temperature within the circulator. This embodiment particularly utilizes the physical effect of the temperature dependence of the circulator's insulating capacity, whereby the temperature in turn influences the permeability. For example, if the measured quantity indicates a comparatively low insulating capacity, the insulating capacity can be partially, preferably completely or maximally, restored by regulating the temperature. The electrothermal component advantageously enables controlled temperature regulation of the circulator. Typically, the electrothermal component is thermally coupled directly to the circulator, especially to the ferrites.In principle, it is conceivable that a heat transfer element, for example a heat sink and / or a gaseous or fluid-based cooling circuit, is provided between the electrothermal component and the circulator.

[0037] One embodiment provides that the electrothermal component is an electrothermal transducer, in particular a Peltier element. Depending on the set current and / or voltage, the electrothermal transducer enables precise control of the temperature of the circulator, especially the ferrites.

[0038] According to the invention, the high-frequency source has a measuring device for measuring an electromagnetic quantity of the backscattered microwaves, wherein the electromagnetic quantity is the measured quantity describing the magnetic permeability of the circulator.

[0039] The electromagnetic quantity describes the amplitude and / or phase of the backscattered microwaves. This electromagnetic quantity can be referenced to or normalized in relation to an electromagnetic quantity of the generated microwaves. For example, it is conceivable to calculate an amplitude difference and / or a phase difference between the generated microwaves and the backscattered microwaves. The control unit is specifically designed to compare the electromagnetic quantity with a setpoint. The setpoint can be a constant value or depend on the magnetic field. For example, the setpoint can be a value between 0 and 2n if the electromagnetic quantity describes the phase of the backscattered microwaves.The setpoint can be a value of a particularly parabolic function over the magnitude of the magnetic field, if the electromagnetic quantity describes the amplitude of the backscattered microwaves.

[0040] One embodiment provides that a directional coupler is placed between the measuring device and the circulator to separate the generated microwaves from the backscattered microwaves. This embodiment advantageously allows the generated microwaves and the backscattered microwaves to be considered separately.

[0041] The linear accelerator system according to the invention comprises the high-frequency source and a linear accelerator unit, wherein the linear accelerator unit has a particle emitter for emitting charged particles, in particular electrons, and cavities for accelerating the charged particles, in particular the electrons, by means of microwaves. The linear accelerator system according to the invention comprises the high-frequency source according to the invention and thus shares the advantages described above. The linear accelerator system is particularly suitable for radiotherapy, materials testing, and / or safety inspection.

[0042] The linear accelerator system is used in particular to accelerate charged particles, especially electrons, along a straight line. The charged particles are accelerated by the high-frequency source to energies above 1 MeV and typically below 20 MeV, for example in the range of 3 to 9 MeV.

[0043] The particle emitter can be, in particular, an electron emitter. The electron emitter can be, in particular, a thermionic emitter, for example, a helical emitter or a spherical emitter, or a cold emitter, for example, with carbon tubes or made of silicon. The electron emitter can have a grid for regulating the electron injection.

[0044] The cavities are, in particular, linear accelerator cavities and are typically evacuated. The cavities form, in particular, a standing wave accelerator or a traveling wave accelerator. The cavities are typically interconnected and arranged in a series, so that the charged particles traverse the cavities sequentially. The particle emitter is usually located at one end of the series of cavities, and an exit port is typically located at the other end. The exit port may be sealed with a vacuum-tight window.

[0045] One embodiment provides that the linear accelerator unit has a target located within the cavities for generating MeV X-rays depending on the accelerated charged particles. The target is typically arranged at one end of the series of cavities opposite the particle emitter. The target can, for example, be part of the exit opening and seal it vacuum-tight. The target is, in particular, a transmission target. The charged particles typically strike the surface of the target at a perpendicular angle. The target is typically in the shape of a disc. The disc is a cylindrical body, usually with a small height relative to its diameter. The target is, in particular, made of a material with a high atomic number (Z) and / or high density, e.g.,Silver, copper, gold, aluminum, rhodium, tungsten, molybdenum, rhenium, zirconium, chromium, cobalt, iron, manganese, vanadium, titanium, tantalum, indium, iridium, or beryllium, or an alloy of the previously described conventional target materials. The target material can be, in particular, tungsten. Advantageously, the target may also contain, for example, rhenium in addition to tungsten, making it tougher and therefore more robust. The target can be in contact with a cooling medium on the side facing away from the electron beam.

[0046] The linear accelerator system with the high-frequency source can be used, for example, in a stationary or mobile configuration. Advantageously, the linear accelerator system can be operated without a dedicated cooling system or with a cooling system with a comparatively low cooling capacity. The linear accelerator system and / or the high-frequency source can preferably be passively cooled.

[0047] The computer program product can be a computer program or comprise a computer program. The computer program product particularly includes the program code means that implement the process steps according to the invention. This allows the process according to the invention to be defined and executed repeatably, and enables control over the transfer of the process according to the invention. The computer program product is preferably configured such that the computing unit can execute the process steps according to the invention by means of the computer program product. The program code means can, in particular, be loaded into a memory of the computing unit and typically executed by means of a processor of the computing unit with access to the memory.When the computer program product, in particular the program code, is executed in the processing unit, all embodiments of the described method according to the invention can typically be carried out. The computer program product is, for example, stored on a physical, computer-readable medium and / or digitally stored as a data packet in a computer network. The computer program product can represent the physical, computer-readable medium and / or the data packet in the computer network. Thus, the invention can also start from the physical, computer-readable medium and / or the data packet in the computer network. The physical, computer-readable medium is usually directly connectable to the processing unit, for example, by inserting the physical, computer-readable medium into a DVD drive or plugging it into a USB port, thereby allowing the processing unit to access the physical, computer-readable medium, particularly for reading.The data packet can preferably be retrieved from the computer network. The computer network can contain the computing unit itself or be indirectly connected to the computing unit via a wide-area network (WAN) or a (wireless) local area network (WLAN or LAN) connection. For example, the computer program product can be stored digitally on a cloud server at a storage location within the computer network and transferred to the computing unit via the WAN over the internet and / or via WLAN or LAN, particularly by accessing a download link that points to the storage location of the computer program product.

[0048] Features, advantages, or alternative embodiments mentioned in the description of the device are also transferable to the method, and vice versa. In other words, claims relating to the method can be further developed with features of the device, and vice versa. In particular, the device according to the invention can be used in the method.

[0049] The invention will now be described and explained in more detail with reference to the embodiments illustrated in the figures. In principle, structures and units that remain essentially the same in the following figure descriptions will be named with the same reference numeral as when the respective structure or unit first appeared.

[0050] They show: Fig. 1 a high-frequency source according to the invention, Fig. 2 a first embodiment of the high-frequency source, Fig. 3 a second embodiment of the high-frequency source, Fig. 4 a linear accelerator system according to the invention with a 3-port circulator, Fig. 5 a linear accelerator system according to the invention with a 4-port circulator, Fig. 6 a method according to the invention, Fig. 7 an exemplary curve of the high-frequency power, Fig. 8 a first control loop of the high-frequency source, Fig. 9 a second control loop of the high-frequency source Fig. 10 a third embodiment of the high-frequency source, Fig. 11 a fourth embodiment of the high-frequency source and Fig. 12 a fifth embodiment of the high-frequency source.

[0051] Fig. 1 The high-frequency source 10 according to the invention is shown in a schematic block diagram.

[0052] The high-frequency source 10 is configured for a linear accelerator system (not shown). The high-frequency source 10 comprises a microwave generator 11 for generating microwaves, a control unit 12, and a circulator 13. The control unit 12 is configured to receive a measurement quantity describing the magnetic permeability of the circulator 13.

[0053] The circulator 13 is a ferritic 3-port circulator with a Y-shape, which is in Fig. 1 The diagram is shown in perspective and features ferrites 13.F for isolating the microwave generator 11 against backscattered microwaves by influencing the phase of the microwaves as a function of a magnetic field 13.B. The magnetic field 13.B is shown purely for illustrative purposes as a dashed directional arrow in Fig. 1 The circulator 13 also includes an electrical phase stabilization element 14. The microwave generator 11 is connected to the circulator 13, but in this embodiment no payload or load is connected.

[0054] The control unit 12 is designed to adjust a current and / or voltage of the electrical phase stabilization element 14 to influence the magnetic field 13.B depending on the received measurement quantity, such that the amplitude difference between the generated microwaves and the backscattered microwaves is maximized.

[0055] Fig. 2 shows a first embodiment of the high-frequency source 10 according to the invention. Fig. 2 A central cross-section through the circulator 13 is shown.

[0056] The electrical phase stabilization element 14 for influencing the magnetic field 13.B comprises a controllable inductive component 15 through which the set current and / or the set voltage flows. The inductive component 15 comprises at least one electromagnetic coil 15.S. The electrical phase stabilization element 14 additionally comprises a permanent magnet 15.P around which the at least one electromagnetic coil 15.S is wound. Fig. 2 Figure 1 shows that two coils 15.S are wound around each permanent magnet 15.P. The inductive element 14 encloses the cavity 13.H of the circulator 13 and the ferrites 13.F. The ferrites 13.F are advantageously arranged between the two coils 15.S. The magnetic circuit comprises, in particular, the yoke 13.J, the at least one electromagnetic coil 15.S, the permanent magnet 15.P, the ferrites 13.F, and the gap in the cavity 13.H.

[0057] Fig. 3 Figure 10 shows a second embodiment of the high-frequency source according to the invention. This embodiment is expressly related to the one described in Figure 10. Fig. 2 The illustrated embodiment can be combined.

[0058] The electrical phase stabilization element 14 comprises a controllable electrothermal component 16, through which the set current and / or the set voltage flows, for influencing the magnetic field 13.B and for regulating a temperature within the circulator 13. The electrothermal component 16 is an electrothermal transducer, in particular a Peltier element 16.P. Fig. 3 The Peltier element 16.P is marked with a snowflake because the electrothermal component 16 regulates the temperature inside the circulator 13 depending on the set current and / or voltage.

[0059] In Fig. 3 It is further shown that the high-frequency source 10 has a measuring device 17 for measuring an electromagnetic quantity of the backscattered microwaves, wherein the electromagnetic quantity is the measurand describing the magnetic permeability of the circulator 13. The electromagnetic quantity describes an amplitude and / or a phase of the backscattered microwaves. The measuring device 17 is connected to the control unit 12 for transmitting the measured quantity.

[0060] Fig. 4 Figure 1 shows a block diagram of a linear accelerator system 20 according to the invention with a 3-port circulator. The linear accelerator system 20 according to the invention comprises the high-frequency source 10 and a linear accelerator unit 21. The linear accelerator unit 21 has a particle emitter for emitting charged particles and cavities for accelerating the charged particles by means of microwaves. The circulator 13 is designed as a 3-port circulator, with the microwave generator 11 connected to the first port, the linear accelerator unit 21 connected to the second port, and a load 13.L connected to the third port.

[0061] Fig. 5 Figure 1 shows a block diagram of a linear accelerator system 20 according to the invention with a 4-port circulator. Compared to the one in Figure 20, the block diagram shows a linear accelerator system 20 with a 4-port circulator. Fig. 4 In the illustrated embodiment, a reflection phase shifter 19, which is part of the high-frequency source 10, is connected to the additional port of the circulator 13. Alternatively, another load can be connected instead of the reflection phase shifter 19. In this embodiment, the linear accelerator unit 21 has a target provided within the cavities for generating MeV X-rays depending on the accelerated charged particles.

[0062] Fig. 5 further shows that a directional coupler 18 is provided between the measuring device 17 and the circulator 13 for separating the generated microwaves and the backscattered microwaves.

[0063] Fig. 6 shows a flowchart of a method according to the invention for operating a high-frequency source 10.

[0064] Process step S100 characterizes the reception of a measured quantity describing a magnetic permeability of the circulator 13 in the control unit 12.

[0065] Procedure step S101 characterizes the setting of a current and / or a voltage of the electrical phase stabilization element 14 to influence the magnetic field as a function of the measured quantity by means of the control unit 12 such that the amplitude difference of the generated microwaves and the backscattered microwaves is maximized.

[0066] Fig. 7 shows a time course of the high-frequency power of the generated microwaves (L1, dashed line) and the backscattered microwaves (L2, dotted line) in an exemplary time interval, with the linear accelerator unit connected as the payload.

[0067] The first rise in L2 typically begins right at the start of pulse L1 and is primarily the result of the reflection of the radio frequency power at the "empty" linear accelerator unit. This means there are no charged particles in the cavities yet. The second rise in L2 usually begins at the end of pulse L1, when the linear accelerator unit briefly acts as a kind of radio frequency source.

[0068] At time T1, i.e. at the beginning of the pulse of the generated microwaves L1, the measured quantity of the backscattered microwaves is, to a first approximation, independent of the frequency matching of the microwave generator 11 to the linear accelerator unit 21 and is dominated by the scattering of the generated microwaves.

[0069] At time T2, the high-frequency source 10 is in a steady state, typically after frequency matching of the microwave generator 11 to the linear accelerator unit 21. The measured quantity of backscattered microwaves is dominated by the input reflection of the circulator 13.

[0070] The control loops shown in the following figures can, in principle, operate at both times T1 and T2.

[0071] Fig. 8 shows a first control loop of the high-frequency source 10.

[0072] Backscattered microwaves L2 are coupled out of the circulator 13 by means of the directional coupler 18 and measured by the measuring device 17 to determine the measured quantity. The measured quantity is transmitted to the control unit 12, which continuously or intermittently minimizes the amplitude of the backscattered microwaves L2 by adjusting the current and / or voltage of the electrical phase stabilization element 14, thereby maximizing the amplitude difference between the generated microwaves and the backscattered microwaves. The electrical phase stabilization element 14 incorporates an inductive component 15 for this purpose.

[0073] Fig. 9 shows a second control loop of the high-frequency source 10.

[0074] In comparison to the first circuit, the measuring device 17 measures the generated microwaves L1 and the backscattered microwaves L2 to determine the measured quantity, which in this case describes the phase difference. The control unit 12 adjusts the current and / or voltage of the electrical phase stabilization element 14 such that the phase difference essentially corresponds to a setpoint.

[0075] Fig. 10 und Fig. 11 Figures 3 and 4 show a partial representation of a third and fourth embodiment of the high-frequency source 10 with a Peltier element 16.P. These two embodiments are essentially based on the embodiment of Figure 1. Fig. 2 , wherein an electrothermal component 16 is used to control the temperature inside the circulator 13.

[0076] The Peltier element 16.P is in Fig. 10 The Peltier element 16.P is thermally coupled directly to the electrothermal component 16 for temperature stabilization by means of a cooling system 22 with a comparatively low cooling capacity. The coupling between the Peltier element 16.P and the cooling system 22 can be achieved by means of a heat sink (not shown). The circulator 13 is thermally coupled directly to the electrothermal component 16. The cooling system 22 has a first cooling circuit, which includes a heat exchanger 23, a heater 24, a pump 25, a distributor 26, and a collector 27.

[0077] Fig. 11 shows in comparison to the one in Fig. 10 In the illustrated embodiment, the circulator 13 is thermally coupled directly to the Peltier element 16.P for temperature stabilization by means of an intermediate cooling circuit 28.

[0078] Fig. 12Figure 1 shows a fifth embodiment of the high-frequency source 10. In contrast to the embodiments featuring the electrothermal component 16, the cooling system 22 is thermally coupled directly to the circulator 13. Thus, the cooling system 22 directly cools the circulator 13. The larger operating temperature range resulting from the comparatively low cooling capacity is compensated for, in particular, by the inductive component 15 through its influence on the magnetic field.

[0079] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is nevertheless not limited by the disclosed examples and other variations can be derived from them by the person skilled in the art without leaving the scope of protection of the invention.

Claims

1. Radiofrequency source (10) for a linear accelerator system (20), having: - a microwave generator (11) for generating microwaves; - a control unit (12); - a circulator (13), which has ferrites (13.F) for isolating the microwave generator (11) from backscattered microwaves by influencing the phase of the microwaves according to a magnetic field (13.B), wherein the circulator (13) has an electrical phase stabilisation element (14), wherein the control unit (12) is designed to receive a measured variable describing a magnetic permeability of the circulator (13), and to adjust in such a way a current and / or voltage of the electrical phase stabilisation element (14) for influencing the magnetic field (13.B) according to the received measured variable, wherein an amplitude difference between the generated microwaves and the backscattered microwaves is a maximum, - and a measuring apparatus (17) for measuring an electromagnetic variable of the backscattered microwaves, characterised in that the electromagnetic variable is the measured variable describing the magnetic permeability of the circulator, wherein the electromagnetic variable describes an amplitude and / or a phase of the backscattered microwaves.

2. Radiofrequency source (10) according to claim 1, wherein the electrical phase stabilisation element (14) for influencing the magnetic field (13.B) has a controllable inductive component (15), through which the adjusted current and / or adjusted voltage runs.

3. Radiofrequency source (10) according to claim 2, wherein the inductive component (15) has at least one electromagnetic coil (15.S).

4. Radiofrequency source (10) according to claim 3, wherein the electrical phase stabilisation element (14) additionally has a permanent magnet (15.P) around which is wound the at least one electromagnetic coil (15.S).

5. Radiofrequency source (10) according to one of the preceding claims, wherein the electrical phase stabilisation element (14) for influencing the magnetic field (13.B) has a controllable thermoelectric component (16), through which the adjusted current and / or adjusted voltage runs, for controlling a temperature inside the circulator (13).

6. Radiofrequency source (10) according to claim 5, wherein the thermoelectric component (16) is a thermoelectric converter, in particular a Peltier element (16.P).

7. Radiofrequency source (10) according to one of the preceding claims, wherein a directional coupler (18) for separating the generated microwaves and the backscattered microwaves is provided between the measuring apparatus (17) and the circulator (13).

8. Linear accelerator system (20), having: - a radiofrequency source (10) according to one of the preceding claims; and - a linear accelerator unit (21), which has a particle emitter for emitting charged particles, and cavities for accelerating the charged particles by means of the microwaves.

9. Linear accelerator system (20) according to claim 8, wherein the linear accelerator unit (21) has a target, which is provided inside the cavities, for producing MeV X-ray radiation on the basis of the accelerated charged particles.

10. Method for operating a radiofrequency source (10) according to one of claims 1 to 7, containing the following steps: - receiving in the control unit (12) the measured variable describing the magnetic permeability of the circulator (13), - adjusting in such a way by means of the control unit (12) a current and / or voltage of the electrical phase stabilisation element (14) for influencing the magnetic field according to the measured variable that an amplitude difference between the generated microwaves and the backscattered microwaves is maximised.

11. Computer program product, which can be loaded directly into a memory of a control unit and has program code means in order to perform a method according to claim 10 when the computer program product is executed in the control unit.

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