RU2702140C1 - Superconducting compact isochronous cyclotron - Google Patents

Abstract

FIELD: magnets.

SUBSTANCE: invention relates to superconducting compact isochronous cyclotron. Invention can be used in creation of compact isochronous cyclotrons on superconducting magnets in medicine for treating oncological diseases and new growths, as well as in scientific research. Cyclotron includes at least three pairs of sectors of magnets arranged in symmetry with median plane with variable azimuth length and varying vertical clearance between sectors (7). Clearance height decreases from center to outlet zone in middle acceleration zone (5) and, reaching minimum value in output zone (3), increases to edge of magnet pole (4).

EFFECT: technical result is possibility of creation of compact structure of magnet forming isochronous field in middle zone of acceleration and falling in output zone, providing good beam focusing at cyclotron output.

1 cl, 5 dwg

Description

Technical field

The superconducting compact isochronous cyclotron belongs to the field of particle accelerator technology. Currently, accelerators of this type are mainly used in medicine, for the treatment of cancer and neoplasms using proton therapy, and for the production of various medical isotopes in nuclear medicine. One of the main problems in the development and design of compact isochronous cyclotrons for proton therapy with superconducting coils (8), with a magnetic field (3-4 T.), are the difficulties in ensuring the required beam parameters at the output of the accelerated particle beam from the compact cyclotron. When a particle beam is removed from the cyclotron, it enters the zone of a sharply decreasing magnetic field at the edge of the magnet pole, as a result of which it refocuses and grows in size. An important criterion for the quality of the beam for proton therapy is to ensure the smallest divergence of the particle flux along the edges of the beam while maintaining the constant geometric dimensions of the output beam (beam emitance is less than or equal to 5π mm mrad). The relevance of developing more advanced isochronous cyclotrons with optimal parameters for proton therapy is due to the intensive development of proton therapy in the world over the past ten years and the doubling of the number of newly built specialized medical proton therapy centers in the world over the past five years.

State of the art

C235", Proceedings of the 1997 Particle Accelerator Conference Vancouver, B.C., Canada 12-16 May 1997) (прототип) помимо секторов с переменной азимутальной протяженностью (9), используется вертикальный зазор эллиптической формы, уменьшающийся по высоте от центра к краю полюса магнита.The formation of the isochronous magnetic field of the cyclotron in the middle acceleration zone, as a rule, is carried out by changing the azimuthal length of the magnet sectors (6), correcting the magnetic field of the tire sectors and tires of the magnet valleys. Several different approaches to the formation of the isochronous field of the cyclotron are known in the literature. For example, in the superconducting cyclotron of Sumitomo Heavy Industries (Japan) (N. Tsutsui, et al, Design Study of a Superconducting AVF Cyclotron for Proton Therapy, Cyclotrons 2013: Proceedings of the 20th International Conference on Cyclotrons and their Applications, p 102. ) the variable azimuthal length of the magnet sectors is used, forming a narrow, vertical gap that does not vary in height. The cyclotron of ACCEL / Varian (USA) (Volker Schirrmeister, "Particle Therapy with the Varian / ACCEL 250 MeV SC Proton Cyclotron", 1st Workshop HADRON BEAM THERAPY OF CANCER, ERICE-SICILY, 24 APRIL -1 MAY 2009) uses a wide, more than 50 mm clearance with a constant height. In the cyclotron of IBA (Belgium), modification C-235 (D. Vandeplassche, et al, "Extracted beams from

C235 ", Proceedings of the 1997 Particle Accelerator Conference Vancouver, BC, Canada 12-16 May 1997) (prototype) in addition to sectors with variable azimuthal length (9), a vertical elliptical gap is used, decreasing in height from the center to the edge of the magnet pole.

The disadvantage of this and other cyclotrons is that when a proton beam is removed from the cyclotron, it falls at the edge of the magnet pole into the zone of a sharply decreasing magnetic field, as a result of which it refocuses and grows in size.

Disclosure of invention

The technical task performed by the invention is the possibility of forming an isochronous magnetic field in the middle acceleration zone and a decreasing magnetic field in the output zone (see Fig. 4), which ensures beam extraction with the parameters required for proton therapy (beam emitance is less than or equal to 5p mm. mrad)

The solution to the technical problem is due to the fact that the height of the gap relative to the median plane (1) decreases from the center to the exit zone and, having reached a minimum value in the exit zone, increases to the edge of the magnet pole.

List of figures:

FIG. 1 The gap between the sectors of the magnet

1. Median plane

2. The central axis, the center of the cyclotron

3. The zone of beam extraction from the cyclotron

4. The edge of the magnet pole

5. Middle acceleration zone

b. Variable Azimuthal Magnet Sectors

7. The height of the gap between the poles of the magnet (variable)

8. Superconducting coils placed in a cryostat

FIG. 2. The horizontal section of the cyclotron

6. Sectors of a variable azimuthal magnet

9. The azimuthal extent of the sector

10. The initial radius of acceleration of the particle beam

11. The final radius of the particle beam in the exit zone from the cyclotron

FIG. 3. The beam envelope in the horizontal plane (a), in the vertical plane (b), where along the X axis is the distance traveled by the beam in the exit zone (mm.), Along the Y axis is the beam envelope (mm), h is in the horizontal plane (Fig. 3 a), z - in the vertical plane (Fig. 3 b)

12. Particle trajectory during the passage of an electrostatic deflector beam

13. Particle trajectory during the passage of the beam at the edge of the magnet sector

14. Particle trajectory during the passage of the valley of the cyclotron magnetic system

15. Particle trajectory during the passage of the beam of the 1st magnetic channel

16. Particle trajectory during the passage of the beam of the 2nd magnetic channel

17. Particle trajectory during the passage of a magnet yoke beam

FIG. 4 Beam emitance in the horizontal plane (a), in the vertical plane (b), where along the X axis the position of the beam particles (mm), along the Y axis the momentum of the particles (px, mrad)

FIG. 5 Graph of magnetic field induction,

where along the X axis is the distance from the center (mm.), along the Y axis are the values of the magnetic field induction (T)

18. The area of the isochronous magnetic field

19. The region of a decreasing magnetic field in the zone of output of the particle flux from the cyclotron

The implementation of the invention

The described invention is applicable mainly to compact isochronous cyclotrons with a magnetic field of 3 to 4 T. The result of the invention is a physical design of an isochronous cyclotron with an average magnetic field of up to 3.6 T., including 3-D models of the main systems of the cyclotron. This cyclotron has a gap of variable height (7) between the sectors of the magnet (6). The gap has a complex shape, tapering from the center (2) and the middle zone (5) to the exit zone (3) and expanding from a point with a minimum clearance height to the edge of the magnet pole (4).

Device execution example

To study the applicability of the proposed device of the magnetic system of the cyclotron, mathematical modeling was carried out. The analysis was carried out on the example of a compact isochronous cyclotron with an average magnetic field of up to 3.6 T.

Modeling and calculation of the magnetic field of the cyclotron was carried out using the program CST Studio and Comsol MultyPhysics

The variable height of the gap in the interval from the center to the output zone was determined by the formula

Half Gap = a (s - R / mm) ^b - d (c - R / mm)

Where Half Gap- half the maximum height of the vertical gap in the interval from the center to the output zone

The variable height of the gap in the interval from the point with the minimum value of the height of the gap to the edge of the magnet pole was determined by the formula

Half Gap (extraction zone) = Half Gap min + (R-R0) * M / (Re-R0)

Half gap (extraction zone) - half the value of the maximum height of the vertical gap in the interval from the point with the minimum value of the height of the gap to the edge of the magnet pole (4).

Where a, b, c, d are constants selected empirically (selection method), in order to obtain conditions for the formation of an isochronous field

a - a calculated parameter that determines the maximum value of the vertical gap in the center;

b - a calculated parameter that determines the angle of curvature of the gap at a point with a minimum value of the gap;

c - a calculated parameter that determines the minimum gap value, selected so that the minimum gap falls at the end of the main acceleration zone;

d is a parameter correcting the angle of inclination of the gap;

R is the radius of the cyclotron;

R0 is the radius of the magnet sector in the center of the cyclotron (10);

Re is the radius of the magnet sector in the zone of beam extraction from the cyclotron (11);

For a compact isochronous cyclotron with an average magnetic field of up to 3.6 T.: a = 2.7; b = 0.37; c = 610; d = 0.0175; R is from 0 to 630 mm

The calculation results confirm the possibility of achieving an isochronous field with an accuracy of 1 Gauss and obtaining the required frequencies of betatron oscillations.

In the graph presented by the simulation results in FIG. Figure 3 shows that the envelope of the beam in the horizontal plane (a) and vertical plane (b) does not go beyond 5 mm.

A beam of particles passing through the electrostatic deflector (12) is focused along the edge of the sector (13), then passes through the valley of the magnet (14) through the first magnetic channel (15) and the second magnetic channel (16) and exits through the yoke of the magnet (17) )

The horizontal beam emmitance shown in FIG. 4 (a) and in the vertical plane shown in FIG. 4 (b) shows that its value is less than or equal to 5π mm. mrad

The graph shown in FIG. 5 shows an increase in the average magnetic field of an isochronous cyclotron (region 18) with an increase in the radius of the trajectory of the particle beam and a sharp decrease in the magnetic field in the zone of exit of the particle beam from the cyclotron (region 19)

Thus, the present invention allows to design a compact structure of a magnet forming an isochronous field in the middle acceleration zone and decreasing in the exit zone, providing good focusing of the beam at the exit from the cyclotron.

Literature:

1. N. Tsutsui, et al, Design Study of a Superconducting AVF Cyclotron for Proton Therapy, Cyclotrons 2013: Proceedings of the 20th International Conference on Cyclotrons and their Applications, p 102.

2. Volker Schirrmeister, "Particle Therapy with the Varian / ACCEL 250 MeV S.C. Proton Cyclotron", 1st Workshop HADRON BEAM THERAPY OF CANCER, ERICE-SICILY, 24 APRIL - 1 MAY 2009

3. D. Vandeplassche, et al, "Extracted beams from IBA's C235", Proceedings of the 1997 Particle Accelerator Conference Vancouver, B.C., Canada 12-16 May 1997

Claims (1)

A superconducting compact isochronous cyclotron, which includes at least three pairs of magnet sectors with a variable azimuthal length and a vertical gap between these sectors located symmetrically in the median plane, characterized in that the height of the specified gap decreases from the center to the exit zone and, reaching a minimum values in the output zone increases towards the edge of the magnet pole.

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