Abstract
A particle accelerator for creation of a bunched particle beam and a method for the operation of such a particle accelerator are provided, wherein the particle accelerator includes an HF source and a directional coupler for splitting HF power of the HF source of an HF side into at least a first and a second HF power coupler of a cavity side for coupling in the HF power into at least one accelerator cavity. A. non-reciprocal phase shifter is inserted on the cavity side between the directional coupler and the second HF power coupler, and an HF load is connected on the HF side to the directional coupler, where the non-reciprocal phase shifter is configured to pass a reflected HF wave of the second HF power coupler with phase delay in the direction of the directional coupler in such a way that a destructive interference of the reflected HF waves of the first and second power couplets occurs in the directional coupler in the direction of the source on the HF side.
Claims
1. Particle accelerator, for creation of a bunched particle beam, comprising an HF source and a directional coupler for splitting an. HF power of the HF source on an HF side into at least a first and a second HF power coupler of a cavity side for coupling HF power into at least one accelerator cavity wherein a non-reciprocal phase shifter is inserted on the cavity side between the directional coupler and the second HF power coupler, and an HF load is connected on the. HF side to the directional coupler, where the non-reciprocal phase shifter is configured to pass a reflected HF wave of the second HF power coupler with phase delay in the direction of the directional coupler in such a way that a destructive interference of the reflected HF waves of the first and second power couplers occurs in the directional coupler in the direction of the HF source on the HF side.
2. Particle accelerator according to claim 1, wherein the directional coupler is a 4-port directional coupler, in particular a 3 dB directional coupler.
3. Particle accelerator according to claim 1, wherein the non-reciprocal phase shifter is configured to pass through an adjustably changeable phase delay of the reflected HF wave.
4. Particle accelerator according to claim 1, wherein at least a second, non-reciprocal phase shifter is comprised, which is inserted on the cavity side between the directional coupler and an HF power coupler.
5. Particle accelerator according to claim 1, wherein at least a third HF power coupler (26c) is comprised, which is connected via at least one second directional coupler to the cavity side of the first directional coupler, and which couples HF power into the accelerator cavity at a further coupling-in point.
6. Particle accelerator according to claim 5, wherein a second HF load is connected to an HF side of the second directional coupler.
7. Particle accelerator according to claim 5, wherein a further non-reciprocal phase shifter is inserted between the first directional coupler and the second directional coupler.
8. Particle accelerator according to claim 1 wherein an HF switching element is comprised, which can disconnect the second HF power coupler from the directional coupler.
9. Method for the operation of a particle accelerator according to claim 1, comprising adjusting the phase delay of the non-reciprocal phase shifter such that a reflected HF wave of the second HF power coupler is superimposed on a reflected HF wave of the first power coupler in the directional coupler in such a way that a destructive interference of the returning HF waves on the HF side results in the direction of the HF source.
10. Method for the operation of a particle accelerator according to claim 9, wherein the phase delay of the non-reciprocal phase shifter (22) is controlled.
11. Method according to claim 10, wherein control of the phase delay of the non-reciprocal phase shifter regulates an HF power input into the accelerator cavity.
Description
BRIEF DESCRIPTION OF THF DRAWINGS
[0024] Further advantages emerge from the description of the drawings below. Exemplary embodiments of the invention are illustrated in the drawings. The drawing, description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into useful further combinations.
[0025] The drawing shows in:
[0026] FIG. 1 a schematic illustration of a first embodiment of the invention,
[0027] FIG. 2 schematically a second exemplary embodiment of the invention,
[0028] FIG. 3 a further schematically illustrated exemplary embodiment of the invention,
[0029] FIG. 4 a further schematically illustrated embodiment of the invention with three coupling-in points,
[0030] FIG. 5 a further schematically illustrated, embodiment of the invention with four coupling-in points.
[0031] The same reference nu numerals have been used to identify elements that are identical or similar in the figures.
DETAILED DESCRIPTION
[0032] FIG. 1 illustrates a first embodiment 100 of a particle accelerator 10. The particle accelerator 100 comprises a particle source 12, for example an electron source with a heatable cathode, which is heated and emits electrons. The electrons emitted are focused by a focusing segment 62, for example a solenoid magnet, not illustrated, and passed to a resonator cavity 18. The accelerator cavity 18 comprises a large number of mechanically connected individual resonator cavities 24, into which HF power can be coupled, where one mode, usually the basic mode of the HF power, creates electrical fields in the direction of acceleration with the correct phase for the flight speed of the particles, in order to transmit a respective acceleration pulse to the particles. Two power couplers 26a and 26b are arranged at the front and rear ends of the accelerator cavity in order to couple the HF power into the accelerator cavity 18. The power couplers serve to couple HF power into the individual resonator cavities 24 in order to develop the acceleration modes, and in some cases to couple out higher modes that are excited by the particles, and are unwelcome since they hinder an optimum acceleration. Accordingly, a fraction of the HF power that is supplied via HF waveguides 28, for example hollow waveguides, microstrip or coaxial cables, to the power couplers 26 is reflected again and passed back in the direction of the HF source 14. The HF source 14, for example a magnetron, creates high-frequency power for supply into the accelerator cavity 18, and preferably excites a basic mode of the single resonator cavity 24 that can be coupled as an accelerator mode in the accelerator cavity 18. A 4-port directional coupler 20, comprising an HF side 32 with ports P1 and P4 and a cavity side 34 with the ports P2 and P3, is provided to split the HF energy into the two power couplers 26a and 26b. On the HF side 32, the HF source 14 and an HF load 16 which serves to absorb reflected HF power are connected. The directional coupler 20 is designed to split a power supplied at port P1 to the ports P2 and P3. Power reflected from port P2 or from port P3 is furthermore passed to port P4. The entire reflected energy is thus passed in the direction of the HF load 16, while an HF power of the HF source 14 is split symmetrically between the ports P2 and P3. Anon-reciprocal phase shifter 22 is provided in the waveguide 28 between the port P3 and the second power coupler 26b. The non-reciprocal phase shifter 22 causes a phase shift in the power flowing forward in the direction of the HF power coupler 26b in such a way that this power can be coupled into the accelerator cavity 18 with the correct phase relative to the HF power coupled in by the first power coupler 26a, in order to excite the basic acceleration mode. The magnitude of the forward phase shift is accordingly based on the length and the number of the cavities of the accelerator cavity 18. Power reflected from the second power coupler 26b is delayed in the return phase by the returning branch of the non-reciprocal phase shifter 22 in such a way that it can be superimposed on a reflected HF power of the first power coupler 26a in the directional coupler 20 with destructive interference. The entire reflected and superimposed power of the two HF branches is absorbed in the HF load 16. The HF source 14 is not subjected to reflected power, and can work with an optimised efficiency. The phase delay of the non-reciprocal phase shifter 22 in the forward branch and in the returning branch must be selected in such a way that an optimised power coupling, with the correct phase relative to the power coupled in by the first power coupler 26a, is achieved in the forward branch. The returning reflected HF energy is phase-delayed in such a way that it is superimposed on the reflected energy of the first power coupler 26a with destructive interference in the directional coupler 20. An optimum operation with a high efficiency of the HF power is thus achieved. The accelerated electron beam 60 is guided out of the resonator cavity 18 via a drift tube 64, and can be used for farther purposes, for example as a high-energy beam for the excitation of electromagnetic fields, as a therapy beam for cell irradiation, for basic scientific experiments or for other purposes.
[0033] FIG, 2 illustrates a particle accelerator 10, whose principles are the same as those of FIG. 1, in a second embodiment 102. In contrast to the embodiment according to FIG. 1,, two non-reciprocal phase shifters 22a and 22b are provided on the cavity side 34 of the directional coupler 20 in both HF branches leading to the power coupler 26a and to the power coupler 26b. Each of the two phase shifters 22a and 22b comprise different phase delays in the forward and reverse directions, whose purpose is to couple in the coupled-in HF power in the correct phase and to correlate the reflected HF power of the two branches in such a that they are superimposed destructively in the directional coupler 20 and can be passed on to the HF load 16. This opens up the possibilities of being able to adjust the supplied. HF power in both HF branches, as well as die reflected HF power, over larger ranges than illustrated in the first exemplary embodiment 100 in FIG. 1, in order to achieve an optimum efficiency. The HF section of the particle accelerator 10 can be adapted individually to different accelerator cavities 18 thanks to the adjustability of the two non-reciprocal phase shifters 22a and 22b.
[0034] FIG. 3 illustrates a further exemplary embodiment 104 of a particle accelerator 10. It corresponds substantially to the embodiment of FIG. 1, but both an adjustable non-reciprocal phase shifter 30 and also an HF switching element 36 are provided in the HF branch 28 leading from the 4-port directional coupler 22 to the second power coupler 26b. A second HF coupling-in point of the resonator cavity 18 can be activated by means of the HF switching element 36, which can preferably be switched on or off electronically by a switching signal, such that the power of the particle beam 60 can be significantly increased. The preferably electronically adjustable non-reciprocal phase shifter 30 permits the phase offset of the forward wave as well as of the returning wave to be adjusted individually. The adjustability of the phase of the incoming wave permits a larger treasure of power control of the particle beam 60. The regulation of the returning HF wave accordingly permits a matching to the reflected wave of the first power coupler 26a, in order to operate the HF source 14 at optimised efficiency.
[0035] It is clear that frequency and phase detectors can be provided in the supplied HF branches 28, which output information about the phases of the forward and returning HF waves in the HF waveguides 28 when regulating, for example, the adjustable non-reciprocal phase shifter 30. A controller, not illustrated, enables the adjustment of the phase offset of the phase shifter 22, and permits control of the switching on or off of the HF switching element 36.
[0036] FIG. 4 illustrates a further embodiment 106 of a particle accelerator 10. The basic form of the embodiment 106 illustrated in FIG. 4 corresponds to that of the embodiment illustrated in FIG. 1. In addition, however, to a first and a second power coupler 26a and 26b, the particle accelerator 106 comprises a further power coupler 26c. The power coupler 26c couples HF power in a connecting segment 66 between a first section 18a and a second section 18b of a resonator cavity 18. As a result, HF power can be coupled in at three points of the cavity 18, and the HF power input can thus be significantly increased. To supply the three power couplers 26a, 26b and 26c, the HF power of the source 14 is split by the directional coupler 20a into two partial branches. The first partial branch supplies the power coupler 26a with about 50% of the supplied HF energy. The second partial branch is guided via a first non-reciprocal phase shifter 22a and to an HF side 32 of a second directional coupler 20b. The first non-reciprocal phase shifter 22a is configured to delay a reflected HF wave from the HF side 32 of the second directional coupler 20b in such a way that it can be superimposed on a reflected HF power of the first power coupler 26a in the first directional coupler 20a with destructive interference, and can be passed to the HF load 16a, A second HF load 16b is connected to the HF side 32 at the second directional coupler 20b. The third power coupler 26c is connected to the cavity side 34 of the second directional coupler 20b and, via a further non-reciprocal phase shifter 22b, to the second power converter 26b, each of which supplies about 25% of the HF power. The embodiment 106 thus constitutes a cascaded HF supply, where a further branch, comprising a second directional coupler 20b and a second phase shifter 22b, is connected via a first directional coupler 20a and a first phase shifter 22a. The second directional coupler 20b is connected on its HF side 32 to a second HF load 16b. As a result, reflected powers of the second and third power couplers 26b and 26c can thus be delayed with the correct phase by the second phase shifter 22b and guided to the second HF load 16b. The reflected HF power of the HF side 32 of the second directional coupler 20b is guided via the non-reciprocal phase shifter 22a to the cavity side 34 of the first directional coupler 20a. The reflected HF power can be superimposed on the HF power reflected from the first power coupler 26a in the first directional coupler 20a, and guided in turn into the first HF load 16a.
[0037] A modular structure is proposed in FIG. 4, to which further HF power couplers can be connected, so that a high HF power can be supplied into the accelerator cavity 18. According to the exemplary embodiment of FIG. 4, about 50% of the HF energy is coupled in at the first HF power coupler 28a, and about 25% of the HF energy at each of the further power couplers 28b, 28c.
[0038] In order for an HF energy of the same magnitude to be coupled in at all the coupling-in points, the number of power couplers 28 that should be provided is 2n. The exemplary embodiment of FIG, 5 thus shows a thither embodiment 108 of a particle accelerator 10 having an acceleration cavity 18 with three partial segments 18a, 18b and 18c. Four HF power couplers 28a, 28b, 28c and 28d are provided at the acceleration cavity 18, where about 25% of the energy of the HF source 14 is supplied into the cavity at each power coupler. Two supply networks are connected for this purpose on the cavity side 34 of the first directional coupler 20a, each of which comprise an input-side phase shifter 22a, 22c, followed by a directional coupler 20b, 20c with HF load 16b, 16c, and then a further phase shifter 22b, 22d in a branch to the HF power coupler 26b, 26d. As a result, the same amount of HF energy can be supplied via each power coupler 26, and the power can be adjusted over a wide range by a phase adjustment of the non-reciprocal phase shifter 22a.
[0039] Cascadable power stages can be connected by HF switching elements, where the power and the reflected energy of the HF wave can be adjusted over wide ranges by the provision of controllable non-reciprocal phase shifters. A compact embodiment of a particle accelerator, as can be employed in cancer therapy for the creation of gamma rays, can thus be provided. The bunched acceleration of the particles is achieved in that HF power of the HF source is distributed in equal amplitudes via a 3 dB coupler. The HF wave, can be supplied at the beginning of the accelerator structure, and can be supplied via a fixed phase shifter'with the correct phase into a second coupling-in point. The returning wave of the second coupling-in point is shifted in phase in the non-reciprocal phase shifter in such a way that the superposition of the first wave in the 313 coupler diverts the reflected wave into the HF load. This permits the design of a modular and flexible HF supply section of an accelerator structure, and operation of the HF source with an optimised efficiency, so that a cavity with compact dimensions and low quality can be used to create a high electron beam power.
LIST OF REFERENCE NUMERALS
[0040] 10 Particle accelerator [0041] 12 Particle source [0042] 14 HF source [0043] 16 HF load [0044] 18 Acceleration cavity [0045] 20 4-port directional coupler [0046] 22 Non-reciprocal phase shifter [0047] 24 Single resonator cavity [0048] 26 HF power coupler/HOM coupler [0049] 28 HF waveguide [0050] 30 Adjustable non-reciprocal phase shifter [0051] 32 HF side of the directional coupler [0052] 34 Cavity side of the directional coupler [0053] 36 HF switching element [0054] 60 Particle beam [0055] 62 Focusing segment [0056] 64 Drift tube [0057] 66 Connecting segment/drift tube [0058] 100 Particle accelerator, first embodiment [0059] 102 Particle accelerator, second embodiment [0060] 104 Particle accelerator, third embodiment [0061] 106 Particle accelerator, fourth embodiment [0062] 108 Particle accelerator, fifth embodiment
