EP3244709B1 - Gradient corrector for cyclotron - Google Patents

Gradient corrector for cyclotron Download PDF

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Publication number
EP3244709B1
EP3244709B1 EP16169494.8A EP16169494A EP3244709B1 EP 3244709 B1 EP3244709 B1 EP 3244709B1 EP 16169494 A EP16169494 A EP 16169494A EP 3244709 B1 EP3244709 B1 EP 3244709B1
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EP
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Prior art keywords
hill
recess
edge
peripheral edge
cyclotron
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EP16169494.8A
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German (de)
English (en)
French (fr)
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EP3244709A1 (en
Inventor
Willem Kleeven
Szymon Zaremba
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Ion Beam Applications SA
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Ion Beam Applications SA
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Priority to EP16169494.8A priority Critical patent/EP3244709B1/en
Priority to CA2965016A priority patent/CA2965016C/en
Priority to CN201720510663.7U priority patent/CN207201060U/zh
Priority to CN201710320606.7A priority patent/CN107371316B/zh
Priority to JP2017093672A priority patent/JP6446089B2/ja
Priority to US15/594,525 priority patent/US10064264B2/en
Priority to US15/594,538 priority patent/US9907153B2/en
Priority to US15/594,527 priority patent/US9961757B2/en
Priority to US15/594,534 priority patent/US10278277B2/en
Publication of EP3244709A1 publication Critical patent/EP3244709A1/en
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H13/00—Magnetic resonance accelerators; Cyclotrons
    • H05H13/005—Cyclotrons
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/04—Magnet systems, e.g. undulators, wigglers; Energisation thereof
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/04—Magnet systems, e.g. undulators, wigglers; Energisation thereof
    • H05H2007/043—Magnet systems, e.g. undulators, wigglers; Energisation thereof for beam focusing

Definitions

  • the present invention concerns cyclotrons.
  • it concerns isochronous sector-focused cyclotrons having enhanced focusing of an extracted beam of energized charged particles.
  • a cyclotron is a type of circular particle accelerator in which negatively or positively charged particles are accelerated outwards from the centre of the cyclotron along a spiral path up to energies of several MeV.
  • cyclotron is used in the following to refer to isochronous cyclotrons. Cyclotrons are used in various fields, for example in nuclear physics, in medical treatment such as proton-therapy, or in radio-pharmacy.
  • cyclotrons can be used for producing short-lived positron-emitting isotopes suitable for PET imaging (positron emitting tomography) or for producing gamma-emitting isotopes, for example, Tc99m, for SPECT imaging (single photon emission computed tomography).
  • a cyclotron comprises several elements including an injection system, a radiofrequency (RF) accelerating system for accelerating the charged particles, a magnetic system for guiding the accelerated particles along a precise path, an extraction system for collecting the thus accelerated particles, and a vacuum system for creating and maintaining a vacuum in the cyclotron.
  • RF radiofrequency
  • a particle beam constituted of charged ions is introduced into a gap at or near the center of the cyclotron by the injection system with a relatively low initial velocity. As illustrated in Fig. 3 , this particle beam is sequentially and repetitively accelerated by the RF accelerating system and guided outwards along a spiral path comprised within the gap by the magnetic field generated by the magnetic system.
  • the particle beam reaches its target energy, it can be extracted from the cyclotron by the extraction system provided at a point of extraction, PE.
  • This extraction system can comprise, for example, a stripper consisting of a thin sheet of graphite. For example, H - ions passing through the stripper lose two electrons and become positive. Consequently, the curvature of their path in the magnetic field changes its sign, and the particle beam is thus led out of the cyclotron towards a target.
  • Other extracting systems exist which are well known to the persons skilled in the art.
  • the magnetic system generates a magnetic field that guides and focuses the beam of charged particles along the spiral path until it is accelerated to its target energy.
  • particles charged particles
  • ions used indifferently as synonyms.
  • the magnetic field is generated in the gap defined between two magnet poles by two solenoid coils, 14, wound around these poles. Magnet poles of cyclotrons are often divided into alternating hill sectors and valley sectors distributed around a central axis. The gap between two magnet poles is smaller at the hill sectors and the larger at the valley sectors. A strong magnetic field is thus created in the hill gap portions within the hill sectors and a weaker magnetic field is created in the valley gap portions within the valley sectors.
  • a hill sector has a geometry of a circular sector similar to a slice of cake with a first and second lateral surfaces extending substantially radially towards the central axis, a generally curved peripheral surface, a central surface adjacent to the central axis, and an upper surface defining one side of a hill gap portion.
  • the upper surface is delimited by a first and second lateral edges, a peripheral edge, and a central edge.
  • a particle beam has a cross sectional area.
  • An objective of cyclotrons is to produce charged particle beams having a given energy which are as much focused as possible (i.e. having a small cross sectional area)
  • the variations of the magnetic field created by the succession of hill sectors and valley sectors contributes to the focusing of the beam in a similar way as a light beam can be focused by lenses.
  • the particle beam crosses boundary regions where the magnetic field loses its homogeneity, which is detrimental to the focusing of the particle beam.
  • protruding gradient correctors has, however, several drawbacks.
  • the volume of the vacuum chamber hosting the magnet poles must be increased accordingly, thus requiring more energy and time to pump the gases from the vacuum chamber.
  • the overall weight of the cyclotron is increased because of, on the one hand, the weight of the gradient correctors themselves and, on the other hand, the increased overall size of the outer walls of the vacuum chamber and, consequently, the size of the flux return yoke; both contributing to a substantial increase of the cyclotron weight.
  • the position of the protruding gradient correctors is essential; small deviations of position may yield large variations of the magnetic field.
  • Gradient correctors must be fixed manually by a skilled artisan at precisely the same position of the peripheral surface of all the hill sectors. This is of course, a critical and expensive operation. Fourth, these protruding gradient correctors have the effect of deviating the magnetic field outwards, which pulls outwards the path of the particle beam towards the peripheral edge of a hill gap portion between a pair of opposed hill sectors where the magnetic field loses its homogeneity. This shift also leads to a loss of useful magnetic field and thus requires an increase of the coil current in order to compensate this loss. It is therefore more difficult and expensive to control the properties of the extracted particle beam.
  • US3398308 describes a device for improving the symmetry of the magnetic field to which particles are subjected during acceleration in a cyclotron including a particle extraction system having magnetic components disposed in a peripheral portion of the cyclotron magnetic field region.
  • the device includes several sets of dummy components equal in number to one less than the total number of cyclic variations of the composite magnetic field in the cyclotron.
  • the geometry of the edge of the magnet pole can be modified by radially displacing inwardly a portion of the edge so as to be parallel to the path of the beam exiting the cyclotron.
  • the present invention concerns a magnet pole for a cyclotron comprising at least 3 hill sectors and a same number of valley sectors comprising a bottom surface, said hill sectors and valley sectors being alternatively distributed around a central axis, Z, each hill sector comprising:
  • the recess is generally wedge shaped with a first and second converging lines (preferably straight lines) extending away from the upper peripheral edge, with a converging angle, ⁇ , comprised between 70° and 130°, preferably between 80°and 110°, most preferably 90° ⁇ 5°.
  • the recess can have a converging portion, away from the upper peripheral edge, said converging portion having one of the following geometry:
  • the upper peripheral edge has an azimuthal length, Ah, and wherein the concave portion extends between 3% and 30% of the azimuthal length of the upper peripheral edge, preferably, between 5% and 20%, more preferably, between 8% and 15%.
  • the recess is separated from the first and second upper lateral edges.
  • the recess is adjacent to the first upper lateral edge.
  • the recess can extend over a portion of the peripheral surface.
  • the portion of the peripheral surface correspond to a fraction, ⁇ , of the height of the peripheral surface measured parallel to the central axis between the upper peripheral edge and the lower peripheral line, wherein the fraction, ⁇ , is comprised between 25% and 75%, preferably between 40% and 60%, most preferably between 45% and 55%.
  • the peripheral surface forms a chamfer adjacent to the upper peripheral edge.
  • the upper peripheral edge is an arc of circle which centre is offset with respect to the central axis, and which radius is not more than 85% of a distance from the central axis to a midpoint of the upper peripheral edge, which is equidistant to the first and second upper distal ends.
  • the invention also relates to a cyclotron for accelerating a particle beam over a given path comprised within a gap, said cyclotron comprising first and second magnet poles such as described above, wherein the first and second magnet poles are positioned symmetrically with respect to a median plane normal to the central axes of first and second magnet pole forming said gap in between, with hill gap portion being formed between two opposite hill sectors and valley gap portions being formed between two opposite valley sectors.
  • the recess of a cyclotron has a first and a second recess distal points, said first and second recess distal points being separated from one another by a distance L10, and wherein the hill gap portion between a pair of hill sectors of the first and second magnet poles has an average height, Gh, and wherein the ratio Gh / L10 is comprised between 5 and 100 %, preferably between 10 and 50 %, more preferably, 20 and 33 %.
  • the cyclotron can also comprise a point of extraction, located in a hill gap portion between two opposite upper surfaces of hill sectors of the first and second magnet poles, wherein the given path of the particle beam is an outward spiral path cycling about the central axis until said first point of extraction whence the particle beam can be driven out of the cyclotron with a given energy along an extraction path, and wherein the recess is located downstream from said point of extraction wherein downstream is defined with respect to the direction of the particle beam, such that the extraction path crosses on line of the recess with an angle comprised between 80 and 100°, preferably between, 85 and 95°.
  • the cyclotron further comprises a second point of extraction in a hill sector defining a second extraction path, and comprising a second recess located downstream from the second point of extraction, such that the second extraction path crosses one line of the second recess with an angle comprised between 80 and 100°, preferably between, 85 and 95°.
  • the present invention concerns isochronous sector-focused cyclotrons, hereafter referred to as cyclotron of the type discussed in the technical background section supra.
  • a cyclotron according to the present invention accelerates charged particles outwards from a central area of the cyclotron along a spiral path 12 until they are extracted at energies of several MeV.
  • the charged particles thus extracted can be protons, H + , or deuteron, D + .
  • the energy reached by the extracted particles is comprised between 5 and 30 MeV, more preferably between 15 and 21 MeV, most preferably 18 MeV.
  • Cyclotrons of such energies are used, for example, for producing short-lived positron-emitting isotopes suitable for use in PET imaging (positron emitting tomography) or for producing gamma-emitting isotopes, for example, Tc99m, for SPECT imaging (single photon emission computed tomography).
  • a cyclotron 1 comprises two base plates 5 and flux return yokes 6 which, together, form a yoke.
  • the flux return yokes form the outer walls of the cyclotron and control the magnetic field outside of the coils 14 by containing it within the cyclotron.
  • It further comprises first and second magnet poles 2 located in a vacuum chamber, facing each other symmetrically with respect to a median plane MP normal to a central axis, Z, and separated from one another by a gap 7.
  • the yoke and the magnet poles are all made of a magnetic material, preferably a low carbon steel and form a part of the magnetic system.
  • the magnetic system is completed by a first and second coils 14 made of electrically conductive wires wounded around the first and second magnet poles and fitting within an annular space defined between the magnet poles and the flux return yokes.
  • Each hill sector 3 represented in Fig. 1(b) as light shaded areas, has an upper surface 3U extending over a hill azimuthal angle, ⁇ h .
  • Each of the first and second magnet poles 2 further comprises the same number, N, of valley sectors 4, represented in Fig. 1(b) as dark shaded areas, distributed radially around the central axis Z.
  • the hill sectors 3 and valley sectors 4 of the first magnet pole 2 face the opposite hill sectors 3 and valley sectors 4, respectively, of the second magnet pole 2.
  • the path 12 followed by the particle beam illustrated in Fig. 3 is comprised within the gap 7 separating the first and second magnet poles.
  • the gap 7 between the first and second magnet poles thus comprises hill gap portions 7h defined between the upper surfaces 3U of two opposite hill sectors 3 and valley gap portions 7v defined between the bottom surfaces 4B of two opposite valley sectors 4.
  • the hill gap portions 7h have an average gap height, Gh, defined as the average height of the hill gap portions over the areas of two opposite upper surfaces 3U.
  • Average hill and valley gap heights are measured as the average of the gap heights over the whole upper surface and lower surface of a hill sector and a valley sector, respectively.
  • the average of the valley gap height ignores any opening on the bottom surfaces.
  • the upper surface 3U is defined by (see Fig. 2 ):
  • a hill sector 3 further comprises (see Fig. 2 ):
  • the average height of a hill, Hh, sector is the average distance measured parallel to the central axis between lower and upper lateral edges.
  • An end of an edge is defined as one of the two extremities bounding a segment defining the edge.
  • a proximal end is the end of an edge located closest from the central axis, Z.
  • a distal end is the end of an edge located furthest from the central axis, Z.
  • An end can be a corner point which is defined as a point where two or more lines meet.
  • a corner point can also be defined as a point where the tangent of a curve changes sign or presents a discontinuity.
  • An edge is a line segment where two surfaces meet.
  • An edge is bounded by two ends, as defined supra, and defines one side of each of the two meeting surfaces.
  • R radius of curvature
  • the edge is defined as the geometric line intersecting the two surfaces extrapolated so as to intersect each other with and infinite curvature (1/R).
  • An upper edge is an edge intersecting the upper surface 3U of a hill sector, and a lower edge is an edge intersecting the bottom surface 4B of a valley sector.
  • a peripheral edge is defined as the edge of a surface comprising the point located the furthest from the central axis, Z. If the furthest point is a corner point shared by two edges, the peripheral edge is also the edge of a surface which average distance to the central axis, Z, is the largest.
  • the upper peripheral edge is the edge of the upper surface comprising the point located the furthest to the central axis. If a hill sector is compared to a slice of tart, the peripheral edge would be the peripheral crust of the tart.
  • a central edge is defined as the edge of a surface comprising the point located the closest to the central axis, Z.
  • the upper central edge is the edge of the upper surface comprising the point located the closest to the central axis, Z.
  • a lateral edge is defined as the edge joining a central edge at a proximal end to a peripheral edge at a distal end.
  • the proximal end of a lateral edge is therefore the end of said lateral edge intersecting a central edge, and the distal end of said lateral edge is the end of said lateral edge intersecting a peripheral edge.
  • the upper / lower central edge may have different geometries.
  • the most common geometry is a concave line (or concave curve), often circular, of finite length ( ⁇ 0), with respect to the central axis, which is bounded by a first and second upper / lower proximal ends, separated from one another.
  • This configuration is useful as it clears space for the introduction into the gap of the particle beam and other elements.
  • the first and second proximal central ends are merged into a single proximal central point, forming a summit of the upper surface 3U, which comprises three edges only, the central edge having a zero-length.
  • the transition from the first to the second lateral edges can be a curve convex with respect to the central axis, Z, leading to a smooth transition devoid of any corner point.
  • the central edge is also reduced to a single point defined as the point wherein the tangent changes sign.
  • a hill sector does not extend all the way to the central axis, the central area directly surrounding the central axis is cleared to allow insertion of the particle beam or installation of other elements.
  • the first and second lateral surfaces 3L are preferably chamfered forming a chamfer 3ec at the first and second upper lateral edges, respectively.
  • a chamfer is defined as an intermediate surface between two surfaces obtained by cutting off the edge which would have been formed by the two surfaces absent a chamfer.
  • a chamfer reduces the angle formed at an edge between two surfaces.
  • Chamfers are often used in mechanics for reducing stress concentrations. In cyclotrons, however, a chamfered lateral surface at the level of the upper surface of a hill sector enhances the focusing of the particle beam as it reaches a hill gap portion 7h.
  • the peripheral surface 3P of a hill sector can also form a chamfer at the upper peripheral edge, which improves the homogeneity of the magnetic field near the peripheral edge.
  • the hill sectors 3 and valley sectors 4 must be distributed about the central axis with a symmetry of N.
  • the first and second magnet poles 2 are positioned with their respective upper surfaces 3U facing each other and symmetrically with respect to the median plane MP normal to the respective central axes Z of the first and second magnet poles 2, which are coaxial.
  • the shape of the hill sectors is often wedge shaped like a slice of tart (often, as discussed supra, with a missing tip) with the first and second lateral surfaces 3L converging from the peripheral surface towards the central axis Z (usually without reaching it).
  • the hill azimuthal angle, ⁇ h corresponds to the converging angle, measured at the level of the intersection point of the (extrapolated) upper lateral edges of the lateral surfaces at, or adjacent to, the central axis Z.
  • the hill azimuthal angle, ⁇ h is preferably comprised between 360° / 2N ⁇ 10°, more preferably between 360° / 2N ⁇ 5°, most preferably between 360° / 2N ⁇ 2°.
  • the valley azimuthal angle ⁇ v measured at the level of the central axis Z is preferably comprised between 360° / 2N ⁇ 10°, more preferably between 360° / 2N ⁇ 5°, most preferably between 360° / 2N ⁇ 2°.
  • the valley azimuthal angle ⁇ v can be equal to the hill azimuthal angle, ⁇ h .
  • the largest distance, Lh, between the central axis and a peripheral edge is preferably comprised between 200 and 2000 mm, more preferably between 400 and 1000 mm, most preferably between 500 and 800 mm.
  • the longest distance, Lh is usually less than 750 mm, and can be of the order of 500 to 750 mm, typically 520 to 550 mm.
  • the two magnet poles 2 and solenoid coils 14 wound around each magnet pole,_form an (electro-)magnet which generates a magnetic field in the gap 7 between the magnetic poles that guides and focuses the beam of charged particles ( particle beam) along a spiral path 12 illustrated in Fig. 3 , starting from the central area (around the central axis, Z ) of the cyclotron, until it reaches a target energy, for example of 18 MeV, whence it is extracted.
  • the magnet poles are divided into alternating hill sectors and valley sectors distributed around the central axis, Z. A strong magnetic field is thus created in the hill gap portions 7h of average height Gh within the hill sectors and a weaker magnetic field is created in the valley gap portions 7v of average height Gv > Gh, within the valley sectors thus creating vertical focusing of the particle beam.
  • a particle beam When a particle beam is introduced into a cyclotron, it is accelerated by an electric field created between high voltage electrodes called dees (not shown), and ground voltage electrodes attached to the lateral edges of the poles, positioned in the valley sectors, where the magnetic field is weaker.
  • dees high voltage electrodes
  • ground voltage electrodes attached to the lateral edges of the poles, positioned in the valley sectors, where the magnetic field is weaker.
  • energetic protons H +
  • H + can be extracted by driving a beam of accelerated H - ions through a stripper consisting of a thin foil sheet of graphite.
  • a H - ion passing through the stripper loses two electrons to become a positive, H + .
  • the curvature of its path in the magnetic field changes sign, and the particle beam is thus led out of the cyclotron towards a target (not shown).
  • Other extracting systems are known by the persons skilled in the art and the type and details of the extraction system used is not essential to the present invention.
  • a point of extraction is located in a hill gap portion 7h.
  • a cyclotron can comprise several points of extraction in a same hill portion.
  • more than one hill sector comprises an extraction point.
  • all N hill sectors comprise the same number of points of extraction.
  • the points of extraction can be used individually (one only at a time) or simultaneously (several at a time).
  • Such hill sector of cyclotron according to the present invention comprises a first and second lateral surfaces 3L, a peripheral surface 3P and an upper surface 3U such as defined above.
  • the upper peripheral edge 3up of the upper surface of at least one hill sector comprises a convex portion adjacent to a concave portion with respect to the central axis defining a recess extending partially over a portion of the peripheral surface of the corresponding hill sector.
  • the upper peripheral edge 3up of the upper surface of at least one hill sector comprises 2 convex portions separated by a concave portion.
  • each hill sector preferably, comprises a concave portion 3upc with respect to the central axis defining a recess 10 extending partially over the peripheral surface of the corresponding hill sector between two convex portions.
  • concave means curving in or hollowed inward.
  • the concave portion with respect to the central axis of an edge is a portion of the edge curving towards the central axis. This term is opposed to the term “convex” that means curving out of or extending outward from the central axis.
  • a hill sector comprises at least one recess separated from the lateral edges.
  • Protruding gradient correctors have several drawbacks:
  • recessed gradient correctors instead of protruding gradient correctors has several advantages.
  • the position of the recesses can be precisely manufactured and positioned by numerically controlled machining allowing the optimization of the angle at which the particle beam crosses the peripheral edge of the hill sector.
  • Fig. 4 shows an example of the lines of the magnetic field deviated by the recessing gradient corrector ( Fig. 5(a) ) and without any gradient corrector ( Fig. 5(b) ). It is therefore easier and more predictable to control the properties of the extracted particle beam, and particularly the focusing thereof. This deviation towards the acceleration area also allows the power fed to the coils to be decreased.
  • the upper peripheral edge 3up comprises a first and a second recess distal points 10rdp, defining the boundaries of a recess, and which are defined as the points where the tangent of the upper peripheral edge changes sign or presents a discontinuity.
  • the first and second recess distal points are separated from one another by a distance L10.
  • the recess also comprises a recess proximal point 10rpp defined as the point of the recess located closest to the central axis, Z.
  • the first and second recess distal points 10rdp join the recess proximal point 10rpp by a first and second recess converging edges 10rc.
  • the recess depth, H10 is defined as the height of the triangle formed by the first and second recess distal points 10rdp and the recess proximal point 10rpp, and passing by the recess proximal point 10rpp.
  • the depth of the recess, H10 is comprised between 3% and 30%, preferably, between 5% and 20%, more preferably, between 8% and 15% of the azimuthal length, Ah, of the upper peripheral edge.
  • the ratio of the recess depth, H10, to the largest distance, Lh, between the central axis and a peripheral edge of a hill sector, H10 / Lh is comprised between between 2% and 20%, preferably, between 4% and 15%, more preferably, between 6% and 10%.
  • the upper peripheral edge 3up has an azimuthal length, Ah, measured between the first and second upper distal ends 3ude.
  • the first recess converging edge 10r1 joining the first recess distal point to the recess proximal point has a length L101 and the second recess converging edge 10r2 joining the second recess distal point to the recess proximal point has a length L102.
  • the lengths L101 and L102 of the first and second recess converging edges are comprised between 5 and 30% of the azimuthal length, Ah, of the upper peripheral edge.
  • the distance L10 between first and second recess distal points ranges between 5% and 50%, more preferably, between 10% and 30%, most preferably, between 15% and 20% of the azimuthal length, Ah, of the upper peripheral edge.
  • the recess also extends over a portion of the peripheral surface 3P from the upper peripheral edge 3up towards the lower peripheral line 3lp .
  • the recess thus extends over the peripheral surface over a fraction, ⁇ , of a height of the peripheral surface measured parallel to the central axis between the upper peripheral edge and lower peripheral line.
  • the fraction, ⁇ is preferably, comprised between 25% and 100%, preferably between 40% and 75%, most preferably between 45% and 55%.
  • the concave portion of the upper peripheral edge can have any of the following geometries open between the first and second recess distal points: (a) a rectangle, (b) a trapeze, (c) a triangle having straight edges or curved (inwards or outwards) edges, (d) an arc of circle, (e) two arcs of circle, (f) a parabola, (g) a square, (h) a parallelogram, (i) a polygon, (j) a smooth curve. Basically, any geometry determined by numerical analysis can be implemented.
  • the small base in the case of a trapeze, can comprise the recess proximal point 10rpp, and the large base can be defined by the first and second recess distal points 10rdp.
  • the small base can be defined by the first and second recess distal points 10rdp, and the large base can comprise the recess proximal point 10rpp.
  • a triangle can be scalene, isosceles or equilateral. It can also be right, with the right angle formed at the recess proximal point 10rpp. In the case of two (or more) arc of circle, they can be curved inwards ((e) right) or outwards ((e) left).
  • the concave portion is preferably designed such that one edge thereof intersects the extraction path of a particle beam with an angle of 80-100°, preferably 85-95°, substantially 90°.
  • a recess 10 extends over a portion of the peripheral surface parallel to the central axis. Alternatively, it can extend downwards from the upper surface with an angle with the central axis, Z.
  • the distance L10 and/or the height H10 can increase or decrease independently of one another or simultaneously along the height of the peripheral surface.
  • the area of the cross-section of the recess normal to the central axis, Z can thus decrease or increase with the distance from the upper surface.
  • the geometry and the area of the cross-section of the recess can change over the peripheral surface.
  • the height of the recess can also vary over the peripheral surface.
  • Fig. 7 illustrates some examples of geometries of recesses.
  • the recess can have a shape of: (a) a prism extending from the upper surface parallel to the central axis, (b) a prism extending from the peripheral surface normal to the central axis, (c) a (portion of) pyramid, or more complex volumes extending over the peripheral surface.
  • the recess is generally wedge shaped with the first and second recess converging edges being straight (or slightly curved inwards or outwards) lines.
  • the tip of the wedge corresponds to the recess proximal point and points at the general direction of the central axis.
  • the converging angle, ⁇ , at the tip of the wedge is preferably comprised between 70° and 130°, more preferably between 80° and 110°, most preferably 90° ⁇ 5°.
  • the expressions "inwards” and “outwards” used herein are to be understood as “towards” or “away from” the central axis, respectively.
  • the converging portion of the wedge-shaped recess can have one of the following geometries:
  • the present invention also concerns a cyclotron comprising magnet poles as defined supra.
  • a cyclotron accelerates a particle beam over a given path until a first point of extraction whence the particle beam is driven out of the cyclotron with a given energy.
  • the hill gap portion between a pair of hill of the first and second magnet poles of a cyclotron has an average height, Gh.
  • the ratio of the distance L10 between first and second recess distal points 10rdp to the height of hill gap portion Gh is comprised between 1 and 20, preferably between 2 and 10, more preferably, 3 and 5.
  • the distance L10 can be of the order of 10-100 mm, yielding a ratio L10/Gh which can be comprised between 1-5, preferably between 3 and 3.5, i.e. Gh / L10 ⁇ 1.
  • a point of extraction is located within a hill gap portion adjacent to the peripheral edges of a pair of opposed hill sectors.
  • a recess is located downstream from said first point of extraction wherein downstream is defined with respect to the direction of the particle beam.
  • the recess 10 is precisely machined with respect to the point of extraction and to the extraction path such that the particle beam intersects the first converging recess edge 10r1 with an angle of 90° ⁇ 15°.
  • the particle beam thus leaves the hill gap portion substantially normal to the magnetic field, which improves the focusing of the extracted particle beam.
  • the position and the geometry of the recess are determined by numerical computation and/or testing.
  • the cyclotron may further comprise a second point of extraction, PE2, located downstream from the first point of extraction, PE1, and within the same hill gap portion of the same pair of opposed hill sectors.
  • the particle beam can be driven out of the cyclotron at said second point of extraction with the same energy as at said first point of extraction.
  • the hill sector comprising the two extraction points also comprises two recesses, each located downstream from a corresponding point of extraction.
  • Fig. 9 shows an example of a preferred embodiment of a magnet pole for a cyclotron according to the present invention.
  • the upper peripheral edge 3up is bounded by a first and a second upper distal ends
  • the upper peripheral edge of a hill sector comprises an arc of circle 3ac which centre is offset with respect to the central axis, and which radius, Rh, is not more than 85 % of a distance, Lh, from the central axis to a midpoint of the upper peripheral edge, which is equidistant to the first and second upper distal ends (Rh / Lh ⁇ 85%).
  • the ratio Rh / Lh of the radius, Rh, to the distance Lh is not more than 75% (Rh / Lh ⁇ 75%), more preferably not more than 65% (Rh / Lh ⁇ 65%).
  • homothetically approximate the orbit is meant that the arc of circle portion of the upper peripheral edge and the last orbit of particle adjacent to the point of extraction are both arcs of circle sharing the same centre with different radii. The arc of circle is thus approximately parallel to the portion of said last orbit directly adjacent to and upstream from the extraction point.
  • the length of the path of the extracted orbit and the angle between the orbit and the upper peripheral edge becomes independent of the azimuthal position of the extracting system (for example a stripper).
  • the characteristics of the extracted beam are (nearly) independent of the position of the point of extraction.
  • the arc of circle extends from the first upper distal end to the second upper distal end of the upper peripheral edge, thus defining the whole peripheral edge of a hill sector and the centre of the arc of circle lies on the bisector of the upper surface, said bisector being defined as the straight line, joining the central axis to the midpoint of the upper peripheral edge.
  • the peripheral surface forms a chamfer adjacent to the upper peripheral edge.
  • a cyclotron accelerates the particle beam over a given path until a first point of extraction whence the particle beam can be driven out of the cyclotron with a given energy.
  • a hill sector may comprise more than one point of extraction, for example, two.
  • the arc of circle portion of the upper peripheral edges of two opposite hill sectors with respect to the median plan MP, of two magnet poles are parallel to and reproduce homothetically a portion of the given path directly upstream of the first point of extraction.
  • the arc of circle shares the same centre as, and is parallel to a portion of the given path over the whole peripheral edge.
  • upstream and "downstream" are defined with respect to the direction of the particle beam.
  • the particle beam When the particle beam has reached its target energy, it is extracted at a point of extraction and, it then follows an extraction path downstream of the point of extraction. A part of this extraction path lies between the first and second magnet poles and is thus still comprised within the hill gap portion and subjected to the magnetic field. If the pair of opposite hill sectors comprises a first and a second points of extraction, the particle beam can be extracted either at the first or at the second point of extraction or at both. The particle beam then follows either a first or a second extraction path downstream of the first or second point of extraction.
  • the length of the extraction path comprised within the gap downstream of the first point of extraction, L1 , and the length of the extraction path comprised within the gap downstream of the second point of extraction, L2, are substantially equal.
  • the main advantage of having the same length of extraction paths downstream of the first and second points of extraction is to ensure that the particle beam extracted from one point of extraction has similar optical properties as the one extracted from the second point of extraction.
  • Fig. 10 shows an example of a preferred embodiment of a magnet pole for a cyclotron wherein the upper surface of at least one hill sector further comprises:
  • fitting means that the pole insert has a general shape able to be precisely inserted into and nested in the recess.
  • all pole inserts have the same shape and are made of the same material.
  • the pole insert is made of the same material as the corresponding hill sector.
  • the recess extends along a longitudinal axis intersecting the central axis, and it is open ended at both ends and extends from the upper central edge all the way to the upper peripheral edge.
  • the longitudinal axis intersects the upper peripheral edge at a point located at equal distance from the first and second upper distal ends, and wherein the first and second upper distal ends are preferably symmetrical with respect to the longitudinal axis.
  • the pole insert has a general parallelepiped shape, as illustrated in Fig. 6(b) .
  • the recess extends to and is open ended at the upper peripheral edge
  • the distal end of the pole insert 9dc forms a portion of the upper peripheral edge.
  • the portion of the upper peripheral edge formed by the pole insert is preferably not more than 10%, more preferably not more than 5% of the length, Ah, of the upper peripheral edge.
  • this distal end forms a chamfer at the peripheral surface.
  • the pole insert is nested in the recess and is reversibly fastened to the corresponding hill sector. For example, it can be coupled to the hill sector with screws.
  • the pole insert preferably has a prismatic geometry along the longitudinal axis over at least 80% of its length, L9, excluding the converging proximal portion 9p, of length L9p.
  • the ridges between the hill upper surface 3U and the hill lateral surfaces are chamfered, then the corresponding ridges of the proximal portion of the recess can be chamfered too.
  • the topography, illustrated in Fig. 6 , of the pole insert upper surface 9U and/or first and second lateral surfaces 9L can be machined to form grooves 9gu, 9gl either transverse, or parallel to the longitudinal axis, of the upper surface or of a lateral surface.
  • the grooves may extend along a straight, curved or broken line.
  • holes 9hu, 9hl can be drilled through the surfaces.
  • the holes can be blind holes (i.e., of finite depth) or can be through holes.
  • each hill sector comprises a pole insert for symmetry reasons, the pole inserts are thus machined individually or aligned side by side and all machined together. The resulting aspect of the machined pole insert may differ considerably from its aspect before machining.
  • the present invention offers the advantages that it allows the reduction of the size of the vacuum chamber and a decrease of the overall weight of the cyclotron.
  • the position of the recesses can be precisely manufactured and positioned.
  • the magnetic field is deviated inwards by recessed gradient correctors resulting in an inwards shift of the last cycles of the particles path where the magnetic field is more uniform than close to the peripheral edge. It is therefore easier and more predictable to control the properties of the extracted particle beam, and particularly the focusing thereof.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Optics & Photonics (AREA)
  • Particle Accelerators (AREA)
EP16169494.8A 2016-05-13 2016-05-13 Gradient corrector for cyclotron Active EP3244709B1 (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
EP16169494.8A EP3244709B1 (en) 2016-05-13 2016-05-13 Gradient corrector for cyclotron
CA2965016A CA2965016C (en) 2016-05-13 2017-04-25 Gradient corrector for cyclotron
CN201710320606.7A CN107371316B (zh) 2016-05-13 2017-05-09 用于回旋加速器的梯度校正器
CN201720510663.7U CN207201060U (zh) 2016-05-13 2017-05-09 回旋加速器和用于回旋加速器的磁极
JP2017093672A JP6446089B2 (ja) 2016-05-13 2017-05-10 サイクロトロン用グラディエントコレクタ
US15/594,525 US10064264B2 (en) 2016-05-13 2017-05-12 Pole insert for cyclotron
US15/594,538 US9907153B2 (en) 2016-05-13 2017-05-12 Compact cyclotron
US15/594,527 US9961757B2 (en) 2016-05-13 2017-05-12 Peripheral hill sector design for cyclotron
US15/594,534 US10278277B2 (en) 2016-05-13 2017-05-12 Gradient corrector for cyclotron

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP16169494.8A EP3244709B1 (en) 2016-05-13 2016-05-13 Gradient corrector for cyclotron

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EP3244709A1 EP3244709A1 (en) 2017-11-15
EP3244709B1 true EP3244709B1 (en) 2020-01-01

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EP3244709B1 (en) * 2016-05-13 2020-01-01 Ion Beam Applications S.A. Gradient corrector for cyclotron
JP6739393B2 (ja) * 2017-04-18 2020-08-12 株式会社日立製作所 粒子線加速器および粒子線治療装置
CN109362172B (zh) * 2018-11-27 2019-09-13 中国原子能科学研究院 一种高能、强流交变梯度回旋加速器
EP3876679B1 (en) * 2020-03-06 2022-07-20 Ion Beam Applications Synchrocyclotron for extracting beams of various energies and related method
CN116170933B (zh) * 2023-01-09 2023-09-05 中国科学院近代物理研究所 用于应用型等时性回旋加速器的磁场装置
CN118642028B (zh) * 2024-08-12 2024-10-18 陕西正泽生物技术有限公司 一种医用回旋加速器测磁霍尔探头校准方法及装置

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DE1223968B (de) * 1964-11-19 1966-09-01 Licentia Gmbh Sektorfokussiertes Zyklotron
CA966893A (en) * 1973-06-19 1975-04-29 Her Majesty In Right Of Canada As Represented By Atomic Energy Of Canada Limited Superconducting cyclotron
JPS57159000A (en) * 1981-03-26 1982-09-30 Japan Steel Works Ltd Electromagnet pole for circular charged particle accelerator
JPS6251200A (ja) * 1985-08-28 1987-03-05 株式会社日本製鋼所 等時性磁場分布を有するサイクロトロンの磁極構造
JP3456139B2 (ja) * 1998-02-23 2003-10-14 三菱電機株式会社 サイクロトロン装置
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RU2373673C1 (ru) * 2008-06-09 2009-11-20 Федеральное государственное унитарное предприятие "Научно-исследовательский институт электрофизической аппаратуры им. Д.В. Ефремова" Изохронный циклотрон для ускорения нескольких типов заряженных частиц
US8723135B2 (en) * 2012-04-03 2014-05-13 Nissin Ion Equipment Co., Ltd. Ion beam bending magnet for a ribbon-shaped ion beam
EP3244709B1 (en) * 2016-05-13 2020-01-01 Ion Beam Applications S.A. Gradient corrector for cyclotron

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Also Published As

Publication number Publication date
JP6446089B2 (ja) 2018-12-26
CN207201060U (zh) 2018-04-06
CA2965016C (en) 2019-07-30
CA2965016A1 (en) 2017-11-13
CN107371316B (zh) 2019-08-27
JP2017204469A (ja) 2017-11-16
CN107371316A (zh) 2017-11-21
EP3244709A1 (en) 2017-11-15

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