Cyclotron having separate bi-sectors
Patent Information
- Application Number
- EP2023708831
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-03-09
- Filing Date
- 2023-03-08
- Publication Date
- 2025-01-15
AI Technical Summary
Current cyclotrons face challenges in accelerating particles to high energies with high intensity while being simple to manufacture, reliable, and space-efficient, and they struggle with beam extraction and loss minimization.
A cyclotron design with separate non-spiral sectors and field inversion coils, where the magnetic field is reversed between sectors, allowing for improved focusing and beam extraction without the need for a septum, and featuring a bi-sector configuration with slots for enhanced diagnostics and compactness.
This design enables acceleration of particles to higher energies with increased intensity, reduced beam loss, and simplified manufacturing, facilitating the production of radioactive isotopes and high neutron flux applications.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Title: Cyclotron with separate bi-sectors
[0003] Technical field
[0004] The present invention relates to particle accelerators, and more particularly to cyclotrons. These constitute an interesting solution for accelerating heavy particles, protons, molecular hydrogen H2+ and other ions, to high energies for various medical and industrial applications or in the field of nuclear physics research.
[0005] The invention relates more particularly to cyclotrons with separate non-spiraled sectors and with valleys between the sectors in which the direction of the magnetic field of the sectors is locally reversed.
[0006] In the classical type of split-sector cyclotrons, the magnetic structures of the electromagnets consist of a magnetic circuit comprising horizontal yokes and yoke returns joining the horizontal yokes. Excitation coils are arranged around two pole pieces fixed to the horizontal yokes. The assembly consisting of the magnetic circuit and the excitation coils is symmetrical with respect to a horizontal plane called the median plane around which the particles are accelerated and guided.
[0007] Two examples of magnetic split-sector structures for accelerating intense beams are described in the following publications: C. Baumgarten, Current limits of PSI's High Power Cyclotrons: Theory and Practice, September 2021 (classical case of spiral split-sector cyclotron) and P. Mandrillon and M. Conjat “Single Stage Cyclotron for an ADS”; Proceedings of the Int. Conf, on Cyclotrons and their Applications (Zurich-2016), pp. 387-393 (case of non-spiral split-sector cyclotron with valleys with reversed magnetic field)
[0008] In this latest publication, a cyclotron comprising a single excitation coil is proposed. The excitation coil described has a particular shape allowing it to reverse the magnetic field between the pole pieces of the sectors. Such a configuration makes it possible to improve the focusing of the particle beams as well as their extraction. However, the manufacture of such a coil can prove complicated. There is a need to further increase the performance of cyclotrons in order to allow in particular the production of cyclotrons, in particular isochronous cyclotrons, capable of accelerating particles to energies between 10 and approximately 100 MeV and with a relatively high intensity if this is desired, and which are also relatively simple to manufacture, operate reliably and compatible with manufacturing in a relatively small footprint.
[0009] In order to extract high intensity beams without losses, there also remains an imperative need to simplify the extraction of accelerated beams.
[0010] Statement of the invention
[0011] The invention aims to meet all or part of these needs and relates to a cyclotron with separate sectors, comprising:
[0012] - a plurality of sectors called "main sectors", each comprising a ferromagnetic yoke and an excitation coil associated with each main sector mounted on a return of the yoke, each main sector comprising a slot extending radially from a predefined distance from the center of the cyclotron, said slot separating the main sector into two secondary sectors,
[0013] - between the main sectors, accelerating cavities and pairs of field inversion coils, distinct from the excitation coils and arranged on either side of the median plane of the cyclotron.
[0014] Field reversal coils generate a magnetic field with the opposite orientation to that generated by the excitation coils. Preferably, particles are only subjected to this reversal of the magnetic field between sectors from a certain trajectory radius.
[0015] This inversion of the magnetic field at the mid-plane between the sectors has several advantages.
[0016] First, it avoids spiraling of the sectors and increases the vertical focusing properties for accelerating particles to high energies. Preferably, the main sectors each have a plane of symmetry passing through the center of the cyclotron. Therefore, the main sectors have a non-spiral shape, which allows for increased compactness and more space for accelerating cavities and field inversion coils. In addition, thanks to this field inversion, the centers of curvature of the trajectories between the sectors are outside the cyclotron, the trajectory of the extracted particles is therefore much shorter and the extraction of the accelerated beam is facilitated. Optionally, no part necessary for deflecting the extracted beam is required to cross the median plane.
[0017] The invention can thus make it possible, particularly in the case of extraction with separate turns, to avoid the use of a septum and thus limit the problems of beam losses due to collision on the septum and therefore of activation that this causes.
[0018] On the other hand, having field reversal coils separate from the excitation coils allows for simplification of the cyclotron.
[0019] In the present invention, each main sector is divided into two secondary sectors by a slit while keeping a single return yoke, as shown in Figure 3. This improves the vertical focusing of the beams.
[0020] This bi-sector configuration makes it possible to double the periodic magnetic structure of the poles of the main sectors. This makes it possible to avoid resonances of horizontal oscillations, known as betatronics, limiting the maximum energy of the cyclotron and thus allowing acceleration to higher energies.
[0021] Furthermore, the slits define secondary valleys that can be used for several types of beam diagnostics, essential for the acceleration of intense beams.
[0022] Preferably, each slot passes through an axis of symmetry of the corresponding main sector.
[0023] Field reversal coils can be coreless for proton acceleration or iron-cored for molecular hydrogen H2+ acceleration.
[0024] At least one of the accelerating cavities may preferably have a truncation at the junction of its radially outer and rear edges. The truncation may have a general bevel shape. The truncation may extend radially further than the radius at which the magnetic field reverses. The truncation may thus provide useful space for extracting the accelerated beam. In particular, the truncation makes it possible to install an extraction channel, in particular an extraction channel producing a magnetic field gradient necessary for focusing. The rear edge of the cavity is defined relative to the direction of the trajectory of the particles, this rear edge corresponding to the edge of the exit face of the cavity by the particles, as opposed to the front edge which corresponds to the edge of the entry face of the particles into the cavity.
[0025] The radially outer edge corresponds to the edge of the cavity furthest from the cyclotron axis as opposed to the radially inner edge which corresponds to the edge of the cavity closest to the cyclotron axis.
[0026] Preferably, each excitation coil has a shape substantially homothetic to that of the corresponding yoke return. For example, each excitation coil is generally kidney-shaped.
[0027] Each excitation coil can have either two parts arranged on either side of the median plane for the acceleration of protons, or a single-part coil arranged in the median plane for the acceleration of molecular hydrogen H2+.
[0028] In the case of acceleration of molecular hydrogen H2+, the excitation coil is preferably single.
[0029] In the case of proton acceleration:
[0030] • each of the parts of at least one of the excitation coils can deviate from the median plane so as to define an inner exit window on the radially inner side of the coil and an outer exit window on the radially outer side of the coil, these exit windows allowing the extraction of the accelerated beam.
[0031] • Each exit window preferably has the general shape of a gendarme's hat.
[0032] • By “policeman’s hat shape” we mean a shape presenting a portion of a certain concavity which extends on each side by a portion of inverse concavity.
[0033] • For example, the interior and exterior exit windows each have a concave portion towards the median plane which extends on each side by a portion of inverse concavity.
[0034] • At least one of the yokes may include an outlet passage passing through the outlet windows, for accelerating the protons. The cyclotron may have multiple injection, in particular axial injection. For this purpose, the cyclotron may include a multiple injection line, in particular at least two parallel injection lines, as described in application WO2020169846, incorporated here by reference. Several beams are thus accelerated simultaneously, which makes it possible to obtain a higher average intensity.
[0035] The cyclotron according to the invention may be at fixed frequency, in particular of the isochronous cyclotron type.
[0036] The cyclotron can be non-superconducting in the case of proton acceleration.
[0037] The output beam energy is preferably greater than or equal to 10 MeV, most preferably in the range 30 to 100 MeV.
[0038] The output beam intensity is greater than or equal to 3 mA.
[0039] The cyclotron according to the invention can provide a cyclotron capable of accelerating and extracting, in particular without beam losses, at least twice as much intensity as current isochronous cyclotrons, in particular for applications in the fields of isotope production or high neutron fluxes.
[0040] The particles accelerated using the cyclotron according to the invention can be used in numerous applications, for example the production of radioactive isotopes by directing the beam towards a target, or to power an accelerator-driven subcritical nuclear reactor, known as an "ADS", with a cyclotron according to the invention adapted for higher energies, for example several hundred MeV.
[0041] The invention also relates to the use of the system according to the invention for the production of medical radioisotopes and / or the control of a small subcritical reactor for the production of nuclear energy.
[0042] Brief description of the drawings
[0043] The invention may be better understood by reading the detailed description which follows, of non-limiting examples of its implementation, and by examining the attached drawing, in which:
[0044] Figure 1 represents, schematically and partially in perspective, an example of a cyclotron according to the invention, Figure 2 is a view similar to Figure 1 in which the upper part of one of the main sectors is masked,
[0045] Figure 3 is a horizontal section taken in the median plane of the cyclotron according to the invention,
[0046] Figure 4 shows the last round of proton acceleration in the midplane of the cyclotron and the extraction of the beam through the yoke,
[0047] Figure 5 is another perspective view of the cyclotron of Figure 1,
[0048] Figure 6 represents a perspective view illustrating the secondary sectors of a main sector of the cyclotron of Figure 1, and
[0049] Figure 7 represents the last round of the acceleration of molecular hydrogen ions H2+ and their extraction by peeling in a stripper thus delivering 2 H+ protons exiting into the valley.
[0050] Detailed description
[0051] Figure 1 illustrates an example of cyclotron 1, with three separate main sectors according to the invention.
[0052] As illustrated, the cyclotron 1 has main sectors 10. These sectors 10 are distributed around the X axis of the cyclotron and separated by regions called "main valleys" 20. The main sectors each have an axis of symmetry Y passing through the center of the cyclotron.
[0053] The sectors 10 each define an air gap, under vacuum, in which the beam of accelerated particles propagates, the cyclotron generally presenting a symmetrical structure with respect to a median plane PM.
[0054] The sectors 10 comprise a ferromagnetic yoke 13 and excitation coils 30 carried by the return of the yokes 15. The excitation coils 30 generate a magnetic field substantially perpendicular to the median plane. This magnetic field makes it possible to guide the accelerated particles along a trajectory around the axis of the cyclotron.
[0055] In the illustrated example, each excitation coil has a shape substantially homothetic to that of the yoke return 15 carrying it and is kidney-shaped in the illustrated example.
[0056] As illustrated in Figure 2, each main sector 10 is divided into two secondary sectors 11 by a slot 12 passing through the axis of symmetry Y of the main sector. The slot 12 extends radially from a predefined radius r and thus defines a secondary valley 22 between the secondary sectors 11.
[0057] Thus, in the example illustrated, a structure with 3 main sectors forms a "pseudo-6 sector" structure. This "bi-sector" principle is not limited to 3 main sectors.
[0058] In this example, each excitation coil 30 comprises two axially close parts arranged on either side of the median plane PM.
[0059] Cyclotron 1 has accelerating cavities 40 which produce a radiofrequency (RF) electric field to accelerate the particles injected into the cyclotron.
[0060] The injection of particles to be accelerated into the cyclotron can be carried out in various ways. It is preferable to carry out a multi-injection, with injection points distributed angularly around the X axis of the cyclotron. Under these conditions, the cyclotron can simultaneously accelerate several beams injected at these locations.
[0061] In the example illustrated in Figures 1 and 2, an injection line 50 is arranged along the central axis X of the cyclotron. This line 50 comprises a High Voltage platform for the ion sources 51, a first guidance and focusing system 53, a resonant cavity called a grouper 55, a second guidance and / or focusing system 57, a second resonant grouping cavity (not shown) and deflection systems (not shown) making it possible to inject the charged particles into the desired zones of the accelerating cavities.
[0062] The cyclotron 1 also comprises pairs of field reversal coils 60 arranged in the main valleys 20. These field reversal coils 60 are distinct from the excitation coils 30, that is to say the coils 60 do not have a common portion with the excitation coils 30.
[0063] As seen in Figure 1, the coils 60 of each pair are arranged above and below the midplane, respectively. The field reversal coils are preferably coreless for proton acceleration, as shown.
[0064] Such an arrangement of the field reversal coils makes it possible to generate in the main valleys a magnetic field with an orientation opposite to that of the sectors. From a certain radius, the magnetic field at the median plane in the main valleys reverses and becomes negative, reversing the direction of curvature of the trajectories, as can be seen in Figure 4.
[0065] The introduction of reverse field in the valleys 20 allows to increase the vertical focusing properties allowing the acceleration of the particle beam up to high energies.
[0066] Cyclotron 1 is suitable for so-called split-turn extraction, by ensuring that two consecutive trajectories are radially offset sufficiently to allow the beam to be deflected on its last turn.
[0067] As illustrated in Figure 4, in the presence of the reverse field in the valleys 20, the centers of curvature of the particle trajectories in the valleys are outside the cyclotron as the radius of the trajectories increases. The extraction of accelerated beam is therefore facilitated. This extraction can be achieved without the need to introduce parts in the median plane between the extracted beam and the last internal orbit to create the aforementioned curvature.
[0068] In the extraction zone, the accelerating cavity 40 has at the junction of its radially outer 42 and rear 43 edges a bevel-shaped truncation 45. The truncation 45 extends further than the radius at which the magnetic field reverses in the valley 20, as illustrated in Figure 3. This makes it possible to install a gradient extraction channel for the accelerated beam, as can be seen in Figure 4.
[0069] In this extraction zone, as can be seen in particular in Figures 5 and 6, the two parts 32 and 34 of at least one excitation coil deviate from the median plane to define an inner exit window 35 on the radially inner side of the coil and an outer exit window 37 on the radially outer side of the coil. These exit windows allow the extraction of the accelerated beam through the yoke.
[0070] Each exit window thus has a general shape of a gendarme hat for the acceleration of the protons.
[0071] In particular, the interior exit windows 35 and 37 each comprise a concave portion towards the median plane which extends on each side by a portion of inverse concavity.
[0072] The yoke 13 carrying the excitation coil 30 having the two output windows comprises an extraction passage passing through the output windows.
[0073] The invention is not limited to the example just described. The number of main sectors may be different from that shown in the figures.
[0074] The excitation coils surrounding the return yokes can have a shape adapted to these yokes. In the case of the acceleration of molecular hydrogen H2+, the excitation coil 30 is unique. The extraction of the two H+ protons is carried out by peeling using a stripper 46 located at the entrance of the valleys 20 as illustrated in Figure 7.
[0075] The excitation and / or field reversal coils can be superconducting.
Claims
Demands 1. Cyclotron (1) with separate sectors, comprising A plurality of sectors (10), called "main sectors", each comprising a ferromagnetic yoke (13) and an associated excitation coil (30) mounted on a return of the yoke (15), each main sector (10) comprising a slot (12) extending radially from a predefined distance from the center of the cyclotron, said slot separating the main sector into two secondary sectors (11), between the main sectors (15), accelerating cavities (40) and pairs of field reversal coils (60), separate from the excitation coils (30) and arranged on either side of the median plane (PM) of the cyclotron (1).
2. Cyclotron according to claim 1, at least one of the accelerating cavities (30) having at the junction of its radially outer (42) and rear (43) edges a truncation (45).
3. Cyclotron according to any one of the preceding claims, each excitation coil (30) comprising at least two parts (32; 34) arranged on either side of the median plane.
4. Cyclotron according to the preceding claim, the two parts of at least one of the excitation coils (30) moving away from the median plane to define an inner exit window (35) on the radially inner side of the coil and an outer exit window (37) on the radially outer side of the coil, these exit windows allowing the extraction of an accelerated beam.
5. Cyclotron according to the preceding claim, each exit window (35; 37) having a general shape having a portion of a certain concavity which extends on each side by a portion of inverse concavity.
6. Cyclotron according to any one of claims 4 or 5, at least one of the yokes having an exit passage (19) through the exit windows (35; 37), for accelerating protons. . Cyclotron according to any one of the preceding claims, each excitation coil (30) having a general kidney-shaped form, adapted to the profile of the cylinder heads.
8. Cyclotron according to any one of the preceding claims, comprising a single excitation coil (30) for accelerating ions Molecular hydrogen H2+.
9. A cyclotron according to any one of the preceding claims, being a multiple-injection cyclotron, the cyclotron comprising at least two parallel injection lines.
10. Use of the system according to the preceding claim for the production of medical radioisotopes and / or the control of a small subcritical reactor for the production of nuclear energy.