A method of manufacturing a cyclotron, a cyclotron and a method of operating a cyclotron

Abstract

A method of manufacturing a cyclotron (10) for producing a beam (18) of accelerated particles comprises the following steps: A cyclotron set-up is defined, the cyclotron set-up including a number of sectors (12) having an RF cavity (14, 16) of the cyclotron (10), an arrangement of the sectors (12) relative to each other and a cavity type for each of the sectors (12) selected from the group comprising acceleration cavities and flattop cavities. Then, a beam path in the cyclotron (10) is determined for a default operation mode and at least one beam path in the cyclotron (10) is determined for a cavity failure mode in which the radio-frequency cavity (14, 16) of one or more of the sectors (12) is not operational. A position of an extraction device (20) of the cyclotron (10) within the sectors (12) is calculated based on the determined beam paths, and the extraction device (20) is placed at the calculated position. Further, a cyclotron (10) and a method for operating a cyclotron (10) is described.

Description

[0001] A method of manufacturing a cyclotron, a cyclotron and a method of operating a cyclotron

[0002] The invention relates to a method of manufacturing a cyclotron for producing a beam of accelerated particles. Further, the invention also relates to a cyclotron obtained by said method, and a method for operating said cyclotron.

[0003] Cyclotrons are circular particle accelerators in which charged particles, e.g. protons, are accelerated and guided in a spiral-like orbit by electric and magnetic fields. The electric fields are generated by radio-frequency, RF, cavities while the magnetic fields are induced within sector dipole magnets of the cyclotron. The accelerated particles are then extracted from the cyclotron by at least one extraction device like an electrostatic deflector and / or a magnetic device, e.g. an electric septum together with an extraction (electro-)magnet associated with an extraction channel. In accelerator-driven systems, the reliability of the used cyclotron is of great importance, i.e. the ability of the cyclotron to operate with little to no interruptions. One of the main reasons of such interruptions are failures of one or more of the radio-frequency cavities of the cyclotron, which result in a shifted spiral-like orbit that does not allow the accelerated particle beam to be extracted by the extraction device or at least only with reduced beam power.

[0004] One option to compensate for failure scenarios is to adjust injection parameters of the cyclotron. However, adjusting these parameters is complicated and time-consuming, leading to extended downtime periods of the cyclotron.

[0005] Another option is to design parallel redundant systems using at least two cyclotrons such that in a case one of the cyclotrons experiences a failure, the redundant cyclotron can still provide the desired accelerated particle beam. However, the necessity to build and maintain several cyclotrons in a redundant system is not feasible or desirable in terms of costs and space requirements, especially in applications which require high intensity accelerators producing beam powers in the MW range. It is the object of the invention to provide a cyclotron having a high beam reliability and a method for operating such a cyclotron to produce a beam of accelerated particles.

[0006] The object of the invention is solved by a method of manufacturing a cyclotron for producing a beam of accelerated particles. The method comprises the following steps: A cyclotron set-up is defined, the cyclotron set-up including a number of sectors having a radio-frequency (RF) cavity of the cyclotron, an arrangement of the sectors relative to each other and a cavity type for each of the sectors selected from the group comprising acceleration cavities and flattop cavities. Then, a beam path in the cyclotron is determined for a default operation mode and at least one beam path in the cyclotron is determined for a cavity failure mode in which the radio-frequency cavity of one or more of the sectors is not operational. A position of an extraction device of the cyclotron within the sectors is calculated based on the determined beam paths, and the extraction device is placed at the calculated position.

[0007] The invention is based on the idea of placing the extraction device of the cyclotron at a position which is optimized in terms of possible radio-frequency cavity failures. That is, the location of the extraction device is optimized already during manufacturing of the cyclotron by taking into account possible failure modes of the radio-frequency cavities. This optimization is done based on determined beam paths, i.e. based on the beam path of the default operation mode and for at least one other beam path of a cavity failure mode. This results in an optimized set-up of the manufactured cyclotron which requires only minimal adjustments of parameters for operating the cyclotron in case of a radiofrequency cavity failure, thereby ensuring a reliable operation of the cyclotron with no or only minimal interruption times and acceptable losses in terms of beam intensity. Thus, a safe and efficient beam extraction is guaranteed under varying conditions during operation of the cyclotron.

[0008] The term “acceleration cavity” herein denotes a radio-frequency cavity used for accelerating the beam of particles within the cyclotron to the desired level of energy of the beam.

[0009] The term “flattop cavity” herein denotes a radio-frequency cavity used for maintaining a target voltage profile, thereby improving the phase alignment of the beam of particles, especially for insertion and / or extraction of the beam of particles. The target voltage profile is especially maintained by the flattop cavity by flattening a peak of a voltage waveform by superimposing a higher harmonic frequency onto a fundamental radio-frequency acceleration frequency.

[0010] The cyclotron preferably has at least two sectors with an acceleration cavity, and optionally at least one sector with a flattop cavity. With an increasing number of acceleration cavities, the number of possible failure modes and therefore of possible deviations of the beam path increases, which results in a more complex adjustment of parameters for operating the cyclotron if these parameters need to be adjusted during operation of the cyclotron. Thus, it is especially beneficial to take into account multiple failure modes already during manufacturing of the cyclotron and calculate an optimized position of the extraction device to further improve the reliability of the cyclotron in cases in which there are multiple acceleration cavities and / or flattop cavities.

[0011] It is also possible that beam paths in the cyclotron are only determined for cavity failure modes of radio-frequency cavities being an acceleration cavity. The failure of an acceleration cavity has a much higher impact on the resulting beam path in the cyclotron than a failure of a flattop cavity, such that a beneficial tradeoff can be made between the efforts of determining multiple beam paths on the one hand and achieving a sufficiently reliable operation of the cyclotron in different failure scenarios on the other hand by focusing only on the acceleration cavities.

[0012] Generally, the cyclotron set-up may include several subsets of sectors, each of which comprises at least one of the sectors of the cyclotron. A first subset may comprise sectors which each have a radio-frequency cavity. Hence, the first subset of sectors may also be called radio-frequency cavity subset. In contrast thereto, a second subset may comprise at least one sector which does not have a radio-frequency cavity, but can still comprise a magnet. The number of sectors per subset may deviate, which depends on the overall cyclotron set-up and / or the total number of sectors.

[0013] When defining the cyclotron set-up, the first subset of sectors (and optionally the second subset) may be defined accordingly. Determining the beam paths can be achieved by simulating the beam paths and / or by measuring the beam paths. Simulating the beam paths is especially beneficial, as the beam path of the default operation mode and of all considered failure modes can be determined before components of the cyclotron have to be assembled based on the defined cyclotron set-up. Thus, it is possible or at least facilitated to include further adjustments to the cyclotron set-up before constructing the cyclotron, if necessary.

[0014] Simulation of beam paths in a cyclotron can be done based on simulation software being readily available for the skilled person. Possible simulation frameworks are OPAL (Object Oriented Particle Accelerator Library) developed by the Paul Scherrer Institute, PSI, and BMAD (Baby MAD) originally developed at Cornell University. Generally, simulation of the beam paths can be based on Runge Kutta tracking in simulated 3D fieldmaps of the cyclotron, e.g. as described in Bi et al.: “Towards quantitative simulations of high power proton cyclotrons" (Phys. Rev. STAB, 14, 054402 (2011), doi:

[0015] 10.1103 / PhysRevSTAB.14.054402).

[0016] The beam paths can be measured on a constructed cyclotron in a preliminary state in which the cyclotron is in principle already operational but the position of the extraction device can still be adjusted. In this way, the determined beam paths are more closely related to the beam paths which can actually be achieved during operation of the cyclotron.

[0017] It is also possible to combine simulating and measuring beam paths, e.g. by first measuring the beam path for the default operation mode and / or for a cavity failure mode and providing the measured beam paths as input beam path into the simulation model for further determining and / or optimizing the beam paths by simulation.

[0018] Furthermore, it also depends on the state of the manufacturing phase whether the beam paths are determined by simulation and / or measurement. At the beginning of the manufacturing phase, the beam paths may be simulated, whereas measurements are taken into account later.

[0019] The position of the extraction device can be calculated based on a plurality of radial and / or azimuthal locations of the extraction device along the sectors of the cyclotron. By taking into account various possible positions of the extraction device within the cyclotron, an optimized position of the extraction device can be easily identified based on the determined beam paths.

[0020] The position of the extraction device can be calculated using a minimizing function based on a difference of the beam path in the default operation mode and the beam paths of each of the at least one cavity failure modes, in particular wherein the minimizing function depends on turn number and azimuth. In other words, the minimizing function is determined for different turn numbers and azimuth, respectively. Thus, the optimal position of the extraction device can be easily determined by finding a minimum within the minimizing function, preferably the global minimum within the minimizing function.

[0021] The turn number denotes the quantity of circles within the spiral-like orbit the beam of particles experiences within the cyclotron. The azimuth denotes an angular position in the cyclotron.

[0022] E.g., the minimizing function E can be defined according to formula (1) wherein Ncav is the total number of radio-frequency cavities within the cyclotron for which a beam path in a corresponding failure mode is determined, Ro(Turn, 0) refers to the ideal beam path in the default operation mode, i.e. the ideal orbit radius observed from the center of the cyclotron when no radiofrequency cavity failure occurs, Rj(Turn, 0) refers to the beam path, namely the orbit radius observed from the center of the cyclotron, in the cavity failure mode corresponding to the failure of the ithradio-frequency cavity, with the voltage in all remaining radio-frequency cavities increased to compensate for the lost voltage from the failed radio-frequency cavity. “Turn” denotes the turn number of the beam of particles in the cyclotron. 0 denotes the azimuth of the beam of particles. The minimizing function E according to formula (1) relates to a sum of squares of the differences of the orbit radius in the cavity failure mode and the ideal orbit radius.

[0023] Another possible minimizing function can be defined according to formula (2) wherein Ncav, Ro(Turn, 0), Ri(Turn, 0), “Turn” and 0 are defined as described before for formula (1). The minimizing function E according to formula (2) relates to a sum of absolute values of the differences of the orbit radius in the cavity failure mode and the ideal orbit radius.

[0024] Generally, the respective difference of the orbit radius in the cavity failure mode and the ideal orbit radius, namely the deviation from the ideal orbit radius, is called radial shift.

[0025] The calculated position of the extraction device can comprise a radial location and / or an azimuthal location at which the minimizing function has a minimum, preferably the global minimum of the minimizing function. Thus, the optimal position of the extraction device can be determined from the minimizing function(s) in a convenient and efficient manner.

[0026] Particularly, several minimizing functions are taken into consideration, e.g. for different turn numbers at which the extraction shall take place and / or different azimuth locations of the extraction device. From the several minimizing functions, e.g. their respective minima, the position of the extraction device can be calculated, wherein further conditions are taken into account. Notably, the total turn number for the cyclotron set-up, namely at which turn the beam shall be extracted, may not solely depend on the minimum, but also on the desired extraction energy of the beam.

[0027] The radial location of the extraction device depends on the turn number at which the extraction shall take place.

[0028] The azimuth location of the extraction device may be determined by obtaining the respective minima for different azimuths while identifying the global minimum.

[0029] To account for different radio-frequency cavity failure scenarios, the beam paths are preferably determined for a plurality of cavity failure modes, wherein each of the cavity failure modes corresponds to a failure mode in which a different radio-frequency cavity is not operational. It is also possible that beam paths are determined for a plurality of cavity failure modes, wherein each of the cavity failure modes corresponds to a failure mode in which a different radio-frequency cavity is not operational, with the voltage increased only for a selected sub-group of the radio-frequency cavities of the cyclotron, to compensate for the lost voltage from the failed radio-frequency cavity. Such an approach is especially beneficial if certain of the radio-frequency cavities of the cyclotron have a much higher impact on the beam path upon failure of the respective radio-frequency cavities than others. Thus, by focusing on the selected sub-group of radio-frequency cavities, the effort for determining the calculated position of the extraction device can be reduced while still taking into account the most relevant failure scenarios.

[0030] A beam path is especially determined for all cavity failure modes in which one of the radio-frequency cavities being an acceleration cavity is not operational. As the radio-frequency cavities being an acceleration cavity have the most impact on the beam path, the calculated position of the extraction device can be especially optimal for different failure scenarios, if a failure of each of these radio-frequency cavities is taken into account for obtaining the calculated position of the extraction device.

[0031] The cyclotron set-up can further include initial beam parameters defining an injection angle and an injection position of the cyclotron. Thus, the initial beam parameters define injection parameters of the cyclotron. In this case, the method can further comprise determining beam paths in the cyclotron for the initial beam parameters and at least one set of adjusted beam parameters being different from the initial beam parameters. The position of the extraction device is calculated based on the determined beam paths obtained with the initial beam parameters and the adjusted beam parameters. Thus, the optimal position of the extraction device as defined by the calculated position can additionally take into account different sets of initial beam parameters, resulting in a further optimization of the resulting cyclotron. The beam parameters associated to the calculated position, i.e. the optimized position of the extraction device, can be used for later operation of the manufactured cyclotron.

[0032] The object of the invention is further solved by a cyclotron for producing a beam of accelerated particles obtained by the method as described before. The features and advantages of the method of manufacturing a cyclotron as described before apply for the cyclotron obtained by said method, too, and vice versa and it is referred to the explanations given before.

[0033] As the extraction device of the cyclotron has been placed at the calculated position obtained based on the determined beam paths, the cyclotron has excellent reliability and ensures a continuous operation for producing a beam of accelerated particles even in case the cyclotron experiences a radio-frequency cavity failure.

[0034] The object of the invention is also solved by a method of operating the cyclotron as described before, wherein, if it is detected that at least one of the radio-frequency cavities being an acceleration cavity is not operational, a compensation scheme is run, the compensation scheme comprising the following steps: The at least one radio-frequency cavity which is not operational is detuned, and the voltage of remaining radio-frequency cavities of the cyclotron which are still operational and which are acceleration cavities is increased to compensate for the voltage of the at least one detuned radio-frequency cavity which is not operational.

[0035] The features and advantages of the method of manufacturing a cyclotron and the cyclotron as described before apply for the method of operating the cyclotron, too, and vice versa and it is referred to the explanations given before.

[0036] As the extraction device of the cyclotron is placed at the calculated position based on the determined beam paths representing the default mode and the cavity failure mode(s), an easy and fast compensation scheme is sufficient to ensure further operation of the cyclotron. That is, only the voltage of the remaining acceleration cavities have to be adjusted while the non-operational cavities are detuned. No complicated and time-consuming parameter adjustments are necessary, thereby eliminating or at least reducing the downtime of the cyclotron in case of a radio-frequency cavity failure.

[0037] The situation of at least one of the radio-frequency cavities being non- operational especially corresponds to one of the cavity failure modes taken into account during manufacturing of the cyclotron. Consequently, the method of operating the cyclotron is less failure-prone as an error management, namely how to react in case of a failure of a cavity, was already implemented during the manufacturing of the cyclotron. In other words, the cyclotron manufactured is more fail-safe compared to cyclotrons known in the state of the art.

[0038] A not operational radio-frequency cavity can be detected by a sensor of the cyclotron, e.g. a sensor measuring a voltage of the corresponding radiofrequency cavity and / or by a sensor measuring a property of the beam of accelerated particles extracted from the cyclotron like the beam energy and / or the beam current.

[0039] The compensation scheme can further comprise adjusting an operation condition of the extraction device according to the increased voltage of the remaining radio-frequency cavities. That is, slight deviations of the beam path within the cyclotron can be taken into account by the extraction device. E.g., the extraction device can comprise an extraction septum and the operation condition which is adjusted is the magnet strength of the extraction septum.

[0040] To ensure that the voltage of the remaining radio-frequency cavities can still be increased in case at least one of the radio-frequency cavities becomes not operational, in the default mode of the cyclotron, the radio-frequency cavities can be operated at a nominal voltage which is lower than a maximum peak voltage of the respective radio-frequency cavity. The maximum peak voltage of each of the individual radio-frequency cavities denotes the highest voltage achievable by said radio-frequency cavity.

[0041] The maximum peak voltage of an individual radio-frequency cavity can correspond to a maximum voltage value of the sum of voltages of all radiofrequency cavities in the default mode of the cyclotron or at least of all radiofrequency cavities being an acceleration cavity in the default mode of the cyclotron. In this way, the voltage of the respective radio-frequency cavity can be increased in a manner to compensate for the loss of voltage of all further radiofrequency cavities.

[0042] The default mode of the cyclotron defines a situation in which at least all radio-frequency cavities being an acceleration cavity are operational, preferably a situation in which all radio-frequency cavities of the cyclotron are operational. Preferably, the nominal voltage is lower than the maximum peak voltage by a fraction of the maximum peak voltage corresponding to the maximum number of radio-frequency cavities which are compensated for.

[0043] The remaining radio-frequency cavities which are acceleration cavities can form a sub-group of radio-frequency cavities of the cyclotron , and, in the compensation scheme, only the voltage of the remaining radio-frequency cavities can be increased. In this case, the sub-group of radio-frequency cavities is especially chosen to be the relevant radio-frequency cavities needed to achieve reliable compensation if the respective radio-frequency cavity becomes not operational. It is also possible that the sub-group of radio-frequency cavities is defined dependent on which radio-frequency cavity is not operational.

[0044] To further ensure that the beam of accelerated particles has the desired extraction energy even in case a cavity failure occurs, the beam of accelerated particles can be extracted to a beam transport line, wherein the beam transport line comprises a transport line radio-frequency cavity for adjusting the energy of the accelerated particles in the beam transport line. Thus, the cyclotron according to the invention can be a cyclotron for providing the beam of accelerated particles to a beam transport line.

[0045] Preferably, the transport line radio-frequency cavity is only used when the compensation scheme is run or has been run. This ensures that the additional transport line radio-frequency cavity only needs to be operated when there is a need for further adjusting the beam behavior.

[0046] The cyclotron is preferably used as a beam source in an accelerator driven nuclear system and / or in a system for producing radioisotopes for medical applications. In such applications, a supply with the beam of accelerated particles without interruptions as provided by the cyclotron according to the invention is especially beneficial.

[0047] Further advantages and properties of the invention will become apparent from the following description of exemplary embodiments of the invention, which are not to be understood as limiting, and from the accompanying drawings. In the drawings: - Fig. 1 shows a schematic depiction of a first embodiment of a cyclotron according to the invention;

[0048] - Fig. 2 shows an exemplary beam path in the cyclotron of Fig. 1 ;

[0049] - Fig. 3 shows a cross-section of selected parts at an extraction device of the cyclotron of Fig. 1 ;

[0050] - Fig. 4 shows a block diagram of a method according to the invention of manufacturing the cyclotron of Fig. 1;

[0051] - Fig. 5 shows a block diagram of steps of determining beam paths in the method of Fig. 4;

[0052] - Fig. 6 shows a diagram illustrating the interaction of beam paths of the cyclotron with an extraction device according to Fig. 3;

[0053] - Fig. 7 shows a block diagram of steps of calculating an optimized position of the extraction device of Fig. 3;

[0054] - Fig. 8 shows a diagram of an error function used in the method of Fig. 4 in dependence of an azimuthal location of the extraction device of Fig. 3;

[0055] - Fig. 9 shows a diagram illustrating the dependence of a radial shift of beam paths in the cyclotron of Fig. 1 in dependence of an azimuthal location of the extraction device of Fig. 3;

[0056] - Fig. 10 shows a diagram illustrating the interaction of beam paths of the cyclotron with the extraction device of Fig. 3 at an optimized position;

[0057] - Fig. 11 shows a block diagram of a method of operating the cyclotron of Fig. 1 according to the invention; and

[0058] - Fig. 12 shows an exemplary beam path of a second embodiment of the cyclotron according to the invention.

[0059] Fig. 1 shows a schematic depiction of a cyclotron 10 according to the invention. The cyclotron 10 features an eight-sector configuration with eight sectors 12, which in the following and in Fig. 1 are also denoted as first sector 12a to eighth sector 12h counted counter-clockwise along the essentially circular arrangement of the sectors 12. Each of the sectors 12a, 12c to 12h comprises one radio-frequency, RF, cavity 14 or 16 for handling a beam 18 of charged particles which is to be accelerated within the cyclotron 10 (indicated by a dashed line in Fig. 1) by electric fields.

[0060] Preferably, the charged particles forming the beam 18 are protons. However, different types of charged particles can be accelerated by the cyclotron 10, too.

[0061] The cyclotron 10 has different types of RF cavities 14 and 16 which differ in a cavity type of the respective sector 12a and 12c to 12h, wherein the RF cavities 14 are acceleration cavities and RF cavities 16 are flattop cavities. Thus, sectors 12a, 12c and 12e to 12g are of a cavity type “acceleration cavity” and the sectors 12d and 12h are of a cavity type “flattop cavity”.

[0062] Acceleration cavities 14 are used for accelerating the beam 18 to the desired level of energy while flattop cavities 16 are used for maintaining a target voltage profile such to control the phase alignment of the beam 18 of particles within the cyclotron 10.

[0063] The cyclotron 10 comprises a vacuum chamber 19 in which the beam 18 is moved along a spiral-like orbit for acceleration. In the shown embodiment, the beam 18 is moved in a counter-clockwise direction along the spiral-like orbit.

[0064] Fig. 2 shows an exemplary beam path of the cyclotron 10 in which the spirallike orbit of the beam 18 can be better visualized. To facilitate understanding, the positions of the sectors 12a to 12h and of the radio-frequency cavities 14 and 16 are schematically indicated in Fig. 2, too.

[0065] In the shown embodiment, the cyclotron 10 is used to accelerate protons as charged particles of the beam 18 from an initial energy of about 40 to 60 MeV to a extraction energy of about 220 to 300 MeV. This increase in energy necessitates about 55 to 70 turns in the spiral-like orbit within the vacuum chamber 19 according to the shown set-up.

[0066] Of course, the number of sectors 12, the number, type and distribution of radio-frequency cavities 14 and 16, the initial energy of the beam 18, the extraction energy of the beam 18 and the number of turns necessary to achieve the extraction energy of the beam 18 can be different from the set-up as discussed for the shown embodiment. That is, the exact values presented here for the exemplary embodiment are merely meant to facilitate the understanding of the invention.

[0067] The beam path as shown in Fig. 2 can be obtained by simulating the beam path based on the cyclotron set-up, e.g. based on simulation frameworks like OPAL and BMAD. Exemplary beam paths as discussed in the following have been calculated using BMAD.

[0068] Generally, it is also possible to obtain the beam paths by measurements once the cyclotron 10 is set-up in a preliminary state, e.g. is set-up for commissioning.

[0069] For extracting the beam 18 from the cyclotron 10, an extraction device 20 is used that comprises an extraction septum 22 (see Fig. 1). In the shown embodiment, the extraction septum 22 is a magnetic septum and is configured to apply a magnetic field vertical to the course of the spiral-like orbit of the beam 18 passing the extraction septum 22 such to deviate its course radially outwards towards an extraction magnet 24. Of course, a different type of extraction septum 22 could be used, too. E.g., the extraction septum 22 can be an electrostatic septum which is configured to apply an electric field horizontal to the course of the spiral-like orbit of the beam 18.

[0070] The extraction magnet 24 is used for moving the beam 18 to a beam transport line 25 connected to the cyclotron 10 and with another system to which the accelerated beam 18 of particles is supplied, e.g. a nuclear system like a sub- critical transmutation reactor and / or a system for producing radioisotopes for medical applications.

[0071] Within the beam transport line 25, a transport line radio-frequency cavity 26 is arranged which can be used to adjust the energy of the accelerated particles in the beam transport line 25, as will be described later in more detail.

[0072] Fig. 3 shows a cross-section of selected parts of the magnetic extraction septum 22. The extraction septum 22 comprises a main body 27 that is yokeshaped. Within the main body 27, an enclosure 28 is formed that is terminated at opposing ends along the vertical direction R of the cyclotron 10 by a first coil 29 and a second coil 30, respectively used for generating the magnetic field with which the beam 18 is directed towards the extraction magnet 24 (see Fig. 1). The part of the first coil 29 and of the second coil 30, which are located towards the center of the cyclotron 10, are covered by a protection screen 31 , e.g. an aluminum plate, in the direction facing the center of the cyclotron 10.

[0073] The beam 18 which is to be manipulated by the extraction septum 22 must pass through the inner enclosure 28 such to be manipulated by the magnetic field generated by the extraction septum 22.

[0074] Fig. 3 depicts an exemplary position of the beam 18 passing close by or through the extraction septum 22 on the last but one turn (denoted with numeral 32 in Fig. 3) and on the last turn (denoted with numeral 34 in Fig. 3). The radial distance (also called “turn separation”) between the positions 32 and 34 is due to the spiral-like orbit the beam 18 passes within the cyclotron 10, which results in an increasing radial distance of the beam 18 from the center of the cyclotron 10 with each turn passed.

[0075] From Fig. 3, it becomes evident that for the beam 18 to successfully pass the extraction septum 22, it is necessary that the position 34 is within the enclosure 28, but not within a part along the radial direction R defined by distance d which is the sum of the width of the protection screen 31 and of the first coil 29 and / or the second coil 30 in the radial direction R (dependent on the position of the beam 18 along the vertical direction V) and not at a position at which the parts of the first coil 29 and / or the second coil 30 located at the far end from the center of cyclotron 10 begin. Of course, in case the extraction septum 22 comprises different components than shown in Fig. 3 for closing the enclosure 28 towards the center of the cyclotron 10, the relevant distance d will be defined by the sum of the width of said components.

[0076] In the shown embodiment, the distance d is approximately 7.5 mm. However, the distance d of course depends on the extraction device 20 and cyclotron setup at hand.

[0077] To ensure reliable beam extraction, the extraction device 20, specifically the extraction septum 22, is placed within the cyclotron 10 at a calculated position determined during a method of manufacturing the cyclotron 10 according to the invention which will be described in the following. In the method of manufacturing the cyclotron 10, first, a cyclotron set-up is determined (step S1 in Fig. 4). The cyclotron set-up defines the general design of the cyclotron 10 and the energy level of the beam 18 achievable with the cyclotron 10.

[0078] The cyclotron set-up includes the number of sectors 12 of the cyclotron 10, which of these sectors 12 have an RF cavity and of which cavity type the respective sectors 12 are. E.g., for the embodiment of Fig. 1, the cyclotron set-up defines that the cyclotron 10 has eight sectors, that sectors 12a, 12c and 12e to 12g are of cavity type “acceleration cavity”, sectors 12d and 12h are of cavity type “flattop cavity” and that sector 12b has neither an acceleration cavity 14 nor a flattop cavity 16. Hence, the sectors 12a, 12c to 12h relate to a first subset since the sectors 12a, 12c to 12h each have an RF cavity 14 or 16, whereas sector 12b relates to a second subset as it does not have any RF cavity.

[0079] The cyclotron set-up can also comprise further parameters defining the overall cyclotron 10 like the size of the components used, the type of particles to be accelerated, the voltage used in the radio-frequency cavities, the type of extraction septum 22 and the type of the extraction magnet 24.

[0080] The cyclotron set-up also comprises initial beam parameters defining an injection angle and an injection position of the beam 18 into the cyclotron, and optionally further parameters like initial beam energy and target beam energy.

[0081] Then, beam paths of the cyclotron 10 according to the defined cyclotron set-up are determined (step S2 in Fig. 4).

[0082] Specifically, a beam path in the cyclotron 10 is determined for a default operation mode (see also step S21 in Fig. 5). The default operation mode corresponds to a situation in which the cyclotron 10 is running with all of the RF cavities 14 and 16 being operational and being operated at nominal voltage. The nominal voltage is preferably below a maximum peak voltage of the respective RF cavity 14, 16.

[0083] Such a situation corresponds, e.g. to a scenario as indicated in Fig. 3 in which the beam 18 at its last turn is at the position 34 and can reliably be extracted using the extraction septum 22. Further, at least one further beam path is determined being representative for a cavity failure mode, i.e. for a situation in which one of the RF cavities 14 and 16 is not operational, e.g. the radio-frequency cavity 14 of sector 12a, and the voltage of the remaining RF cavities 14 is increased to compensate for the lack of voltage of the not operational RF cavity 14 (see step S22 in Fig. 5). Of course, it is also possible that the voltage is adjusted not only for RF cavities 14, i.e. acceleration cavities 14, but also for RF cavities 16, i.e. flattop cavities 16.

[0084] From the determined beam paths, the positions of the beam 18 at its last but one turn and on its last turn are recorded, and optionally further parameters like energy shift at extraction (see step S23 in Fig. 5).

[0085] Optionally, steps S22 and S23 are repeated for several of the RF cavities 14 used within the cyclotron 10 being not operational, as indicated by a dashed line in Fig. 5. That is, a beam path is determined with the RF cavity 14 of sector 12a being operational, but the RF cavity 14 of sector 12c being not operational, etc.

[0086] Preferably, steps S22 and S23 are repeated at least for all RF cavities 14 being not operational, i.e. beam paths are determined for all failure modes in which one of the RF cavities of sectors having the cavity type “acceleration cavity” being not operational.

[0087] Table 1 shows properties derived from the beam path in the default operation mode and beam paths of different cavity failure modes for the exemplary embodiment of Fig. 1.

[0088] For these calculations, an initial location of the magnetic septum 22 within the sector 12h has been chosen as indicated by a septum 22’ depicted with dashed lines in Fig. 1.

[0089] Table 1 : Properties during cavity failure modes.

[0090] AE denotes the energy shift at extraction of the beam 18, i.e. the difference in energy of the accelerated beam 18 between the default operation mode and the respective cavity failure mode.

[0091] AR denotes the shift of the position of the beam 18 along the radial axis R at the location of the magnetic septum 22 compared to the position in the default operation mode, and the turn separation denotes the distance of the positions of the beam 18 along the radial axis R at the last but one turn and the last turn of the beam 18, wherein a total number of 64 turns have been used for the calculation above, which is the number of turns necessary to reach the extraction energy of about 220 to 300 MeV of the beam 18.

[0092] Fig. 6 shows a diagram illustrating the positions of the beam paths according to Table 1 at the last but one turn and the last turn for different cavity failure modes of the exemplary cyclotron of Fig. 1.

[0093] In Fig. 6, bar 36 indicates the width d of the first coil 29 and the second coil 30, respectively, and the protection screen 31. That is, when the position of the beam 18 during one or more of the failure modes is at least partially overlapping with the area defined by bar 36, the beam 18 will be blocked or at least partially blocked by the extraction septum 22, resulting in an undesirable interruption of the accelerated beam of particles extractable from the cyclotron 10 or at least in a loss of beam intensity.

[0094] Note that in Fig. 6 “cavity 1” refers to the RF cavity 14 of sector 12a of Fig. 1 , “cavity 2” refers to the RF cavity 14 of sector 12c of Fig. 1, “cavity 3” refers to the RF cavity 14 of sector 12e of Fig. 1 , “cavity 4” refers to the RF cavity 14 of sector 12f of Fig. 1, and “cavity 5” refers to the RF cavity 14 of sector 12g of Fig. 1. From the analysis of the recorded beam paths, it becomes evident that it is not optimal when the extraction septum 22 is placed at the position within the sector 12h.

[0095] Thus, in the method of manufacturing a cyclotron 10 according to the invention, a position of the extraction device within the sectors 12a to 12h is calculated, which is an optimized position in terms of reliably producing the beam 18 of accelerated particles (step S3 in Fig. 4).

[0096] First, a minimizing function E is defined, wherein the minimizing function E is based on a difference of the beam path in the default operation mode and the beam paths of each of the at least one cavity failure modes which are to be taken into account, i.e. in the shown embodiment all cavity failure modes representing the failure of one of the acceleration cavities 14 (step S31 in Fig.7).

[0097] The minimizing function E can be defined according to formula (1) or according to formula (2) wherein Ncav is the total number of RF cavities within the cyclotron 10 for which a beam path in a corresponding failure mode is determined, R0(Turn, 0) refers to the ideal beam path in the default operation mode, i.e. the ideal orbit radius observed from the center of the cyclotron when no RF cavity failure occurs, Rj(Turn, 0) refers to the beam path in the cavity failure mode corresponding to the failure of the ithRF cavity, with the voltage in all remaining RF cavities increased to compensate for the lost voltage from the RF cavity not being operational. “Turn” denotes the turn number of the beam of particles in the cyclotron 10. 0 denotes the azimuth of the beam of particles, which corresponds to the azimuthal location of the extraction device 20.

[0098] Fig. 8 shows the error function E as a function of the azimuthal location of the extraction device 20 for different turn numbers of the beam 18 within the cyclotron 10 of Fig. 1, wherein the curve 38 shows the error function for 61 turns of the beam 18, the curve 40 shows the error function for 62 turns of the beam 18, the curve 42 shows the error function for 63 turns of the beam 18, the curve 44 shows the error function for 64 turns of the beam 18, the curve 46 shows the error function for 65 turns of the beam 18 and the curve 48 shows the error function for 66 turns of the beam 18.

[0099] From the error functions, the optimum number of turns can be determined based on a minimum of the error function (step S32 of Fig. 7). In Fig. 8, the minima of the three turn numbers having the lowest minima for the embodiment of Fig. 1 are highlighted by arrows.

[0100] It becomes obvious that a design of the cyclotron 10 using 63 turns of the beam 18 for extraction results in the smallest overall error for all considered failure modes. However, the lower number of only 63 turns results in a lower extraction energy of the beam 18 upon extraction compared to a design of the cyclotron 10 using 66 turns, which results in an almost same error, namely only slightly higher minimum compared to the design of the cyclotron 10 using 63 turns. Thus, based on the error function (and the extraction energy), a choice for finding an optimized position of the extraction device 20, especially of the extraction septum 22, can be determined in terms of azimuthal location and extraction energy of the beam 18.

[0101] Further, based on the determined optimum turn number to be used, the optimized azimuthal location of the extraction device 20 to minimize losses in beam intensity can be calculated based on the determined turn number and the radial shifts AR between the beam path of the default operation mode and the beam paths in the cavity failure modes (see step S33 of Fig. 7).

[0102] Fig. 9 shows a diagram illustrating the radial shift AR in dependence of the azimuthal location for different cavity failure modes.

[0103] Curve 50 corresponds to the RF cavity 14 of sector 12e of Fig. 1 being not operational, curve 52 corresponds to the RF cavity 14 of sector 12c of Fig. 1 being not operational, curve 54 corresponds to the RF cavity 14 of sector 12f of Fig. 1 being not operational, curve 56 corresponds to the RF cavity 14 of sector 12g of Fig. 1 being not operational and curve 58 corresponds to the radiofrequency cavity 14 of sector 12a of Fig. 1 being not operational.

[0104] From Fig. 9, it becomes evident that at an azimuthal location of the extraction device 20 of 4.9 rad gives the overall best performance of the cyclotron 10 in the shown embodiment, which corresponds to a position within the sector 12f as indicated in Fig. 1.

[0105] This is also highlighted by Fig. 10 which is a depiction analogous to Fig. 6 but based on the configuration of the cyclotron 10 with the extraction septum 22 placed at the optimized position calculated based on the determined beam paths and the minimizing functions.

[0106] Table 2 shows properties derived from the beam path in the default operation mode and beam paths of different cavity failure modes for the exemplary embodiment of Fig. 2 after the optimization.

[0107] Table 2: Properties during cavity failure modes after optimization.

[0108] For all RF cavity failure scenarios considered, as well as in the default operation mode (indicated by circles 60 and 62 in Fig. 10 for extraction at 66 turns of the beam 18), the beam 18 can be extracted without the risk that the beam 18 coincides with solid parts of the extraction septum 22.

[0109] Thus, during manufacturing of the cyclotron 10, the extraction septum 22 is placed such to correspond to the calculated location to obtain the robust and reliable cyclotron 10 according to the invention, which provides for excellent operational stability (step S4 in Fig. 4).

[0110] It is also possible that the procedure described before for steps S2 and S3 is re-iterated based on at least one set of adjusted beam parameters such to identify the overall best set-up of the cyclotron 10.

[0111] In the following, a method of operating the cyclotron 10 according to the invention will be described.

[0112] During operation of the cyclotron 10, in case at least one of the RF cavities 14 is not operational, which has been considered during calculation for finding the optimized position of the extraction device 20, a compensation scheme is run.

[0113] First, the RF cavity 14 which is not operational is detuned (step S6 in Fig. 11). That is, said RF cavity is not anymore used for interaction with the beam 18 to be accelerated.

[0114] To compensate for the not functional RF cavity 14 which has been detuned, the voltage of the remaining RF cavities 14 which are still operational is increased, wherein the total voltage increase corresponds to the voltage level of the defective RF cavity 14 such to keep the overall voltage as constant as possible (step S7 in Fig. 11).

[0115] E.g., in the shown embodiment, if the RF cavity 14 of the sector 12a fails, the voltage of the RF cavities 14 of the sectors 12c and 12e to 12g can be increased by 20% for compensation.

[0116] As the cyclotron 10 has been manufactured with an optimized position of the extraction device 20, even when an RF cavity failure occurs, operation of the cyclotron 10 can be maintained without or with minimal downtimes, as only the not functional RF cavity 14 has to be detuned and the voltage of the remaining RF cavities 14 needs to be adjusted. There is no need to change the initial beam parameters like injection angle and injection position.

[0117] However, optionally, an extraction condition of the extraction device 20 can be adjusted according to the increased voltage of the further RF cavities 14, i.e. of the RF cavities 14 still being operational (step S8 in Fig. 11). For instance, the magnet strength used in the extraction septum 22 can be adjusted to compensate for offset effects of the beam 18 due to the increased voltages of the further RF cavities 14.

[0118] Further, the transport line RF cavity 26 can be used to adjust the energy of the accelerated particles in the beam transport line 25 such that deviations from the extraction energy caused by the increased voltages of the further RF cavities 14 can be compensated for within the beam transport line 25 (step S9 in Fig. 11).

[0119] Fig. 12 shows an exemplary beam path of a second embodiment of the cyclotron 10 according to the invention.

[0120] The second embodiment essentially corresponds to the first embodiment such that only differences will be explained below. Same reference numerals denote the same or functionally same components and it is referred to the explanations given above.

[0121] The cyclotron 10 according to the second embodiment has a total of 16 sectors 12a to 12p.

[0122] Twelve sectors have radio-frequency cavities 14, namely sectors 12a, 12b, 12d to 12h, 12j to 12m and 12o, and thus they are of the cavity type “acceleration cavity”.

[0123] Three sectors have radio-frequency cavities 16, namely sectors 12c, 12i and 12n, and thus they are of the cavity type “flattop cavity”.

[0124] Sector 12p has neither an acceleration cavity nor a flattop cavity.

[0125] The respective parts of the cyclotron 10 are displayed in an overlay fashion on the beam path of Fig. 12 for facilitating understanding of the set-up of the cyclotron 10 in the second embodiment.

[0126] The cyclotron 10 is configured to accelerate the beam 18 from an initial beam energy of about 220 to 260MeV to an extraction energy of about 750 to 850 MeV. Of course, as discussed before for the first embodiment, the initial beam energy and the extraction energy can be chosen differently. For manufacturing the cyclotron 10 of the second embodiment, in principle the same strategy can be applied for calculating the optimized position of the extraction device 20.

[0127] Accordingly, based on the determined beam paths, properties during cavity failure modes can be obtained analogously to the procedure discussed above, which are summarized in Table 3 for the second embodiment.

[0128] Table 3: Properties during cavity failure modes before optimization. From the data in Table 3, especially the turn separation, it becomes evident that a failure of an RF cavity 14 within the group of RF cavities 14 in sectors 12d to 12h has the most impact upon operation of the cyclotron 10. Thus, instead of taking all RF cavities 14 of the cyclotron 10 into account for calculating the optimal position of the extraction device 20 (which would correspond to a “global” optimization approach), it can be sufficient to consider only a sub-group of RF cavities 14, i.e. the RF cavities 14 of sectors 12d to 12h (corresponding to a “local” optimization approach).

[0129] Accordingly, both in calculating the optimized position of the extraction device 20 during manufacturing of the cyclotron 10 and in operating the cyclotron 10, only the voltage of the further RF cavities 14 of the sub-group which are still operational are used for compensation of the RF cavity 14 not being operational.

[0130] Table 4 presents the results of this approach for the second embodiment.

[0131] Table 4: Properties during cavity failure modes after optimization.

[0132] From Tables 3 and 4 it becomes evident that a local optimization scheme can be sufficient to maintain operational stability and performance of the cyclotron 10, as the turn separation is considerably improved to be in the order experienced for further RF cavities not considered in the optimization, while at the same time the positional shift AR is minimized.

[0133] Overall, based on detailed tracking of possible beam paths in the cyclotron 10, an optimal set-up of the cyclotron can be realized allowing for an especially reliable production of an accelerated beam of charged particles and an easy way to react to RF cavity failures.

Claims

Claims1. A method of manufacturing a cyclotron (10) for producing a beam (18) of accelerated particles, the method comprising the steps of: defining a cyclotron set-up, the cyclotron set-up including a number of sectors (12) having a radio-frequency cavity (14, 16) of the cyclotron (10), an arrangement of the sectors (12) relative to each other and a cavity type for each of the sectors (12) selected from the group comprising acceleration cavities and flattop cavities; determining a beam path in the cyclotron (10) for a default operation mode and at least one beam path in the cyclotron (10) for a cavity failure mode in which the radio-frequency cavity (14, 16) of one or more of the sectors (12) is not operational; calculating a position of an extraction device (20) of the cyclotron (10) within the sectors (12) based on the determined beam paths; and placing the extraction device (20) at the calculated position.

2. The method of claim 1 , wherein determining the beam paths is achieved by simulating the beam paths and / or by measuring the beam paths.

3. The method of claim 1 or 2, wherein the position of the extraction device (20) is calculated based on a plurality of radial and / or azimuthal locations of the extraction device (20) along the sectors (12) of the cyclotron (10).

4. The method of any one of the preceding claims, wherein the position of the extraction device (20) is calculated using a minimizing function based on a difference of the beam path in the default operation mode and the beam paths of each of the at least one cavity failure modes, in particular wherein the minimizing function depends on turn number and azimuth.

5. The method of claim 4, wherein the calculated position of the extraction device (20) comprises a radial location and / or an azimuthal location at which the minimizing function has a minimum.

6. The method of any one of the preceding claims, wherein beam paths are determined for a plurality of cavity failure modes, wherein each of the cavityfailure modes corresponds to a failure mode in which a different radio-frequency cavity (14, 16) is not operational.

7. The method of any one of the preceding claims, wherein a beam path is determined for all cavity failure modes in which one of the radio-frequency cavities (14) being an acceleration cavity is not operational.

8. The method of any one of the preceding claims, the cyclotron set-up further including initial beam parameters defining an injection angle and an injection position of the cyclotron (10), the method further comprising determining beam paths in the cyclotron (10) for the initial beam parameters and at least one set of adjusted beam parameters being different from the initial beam parameters, wherein the position of the extraction device (20) is calculated based on the determined beam paths obtained with the initial beam parameters and the adjusted beam parameters.

9. A cyclotron (10) for producing a beam of accelerated particles obtained by the method according to any of the preceding claims.

10. A method of operating the cyclotron (10) according to claim 9, wherein, if it is detected that at least one of the radio-frequency cavities (14) being an acceleration cavity is not operational, a compensation scheme is run, the compensation scheme comprising the following steps:- detuning the at least one radio-frequency cavity (14) which is not operational; and- increasing the voltage of remaining radio-frequency cavities (14) of the cyclotron which are still operational and which are acceleration cavities (14) to compensate for the voltage of the at least one detuned radio-frequency cavity (14) which is not operational.

11. The method of claim 10, wherein the compensation scheme further comprises adjusting an operation condition of the extraction device (20) according to the increased voltage of the remaining radio-frequency cavities.

12. The method of claim 10 or 11, wherein, in the default mode of the cyclotron (10), the radio-frequency cavities (14) are operated at a nominal voltagewhich is lower than a maximum peak voltage of the respective radio-frequency cavity (14).

13. The method of any one of claims 10 to 12, wherein the remaining radiofrequency cavities (14) form a sub-group of radio-frequency cavities (14) of the cyclotron (10) which are still operational and which are acceleration cavities, and only the voltage of the remaining radio-frequency cavities (14) is increased in the compensation scheme.

14. The method of any one of claims 10 to 13, wherein the beam (18) of accelerated particles is extracted to a beam transport line (25), wherein the beam transport line (25) comprises a transport line radio-frequency cavity (26) for adjusting the energy of the accelerated particles in the beam transport line (25).

15. The method of any one of claims 10 to 14, wherein the cyclotron (10) is used as a beam source in an accelerator driven nuclear system and / or in a system for producing radioisotopes for medical applications.

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