JPS63310600A - Cyclotron - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application) The invention relates to the application of an axial magnetic field to generate ionized particles at high energy levels required for research and other purposes, including ion bombardment. It concerns a cyclotron, a device that accelerates a beam of ionizing particles along a vertical, generally helical path.

(Prior Art) In a cyclotron, a beam of ionized particles passes between a pair of electrodes to which voltages of opposite polarity are applied. Each time an ionized particle transitions between the differential voltages of a pair of electrodes, the particle gains energy.

The voltage applied to the electrodes is a radio frequency AC voltage, and is applied at a frequency that is synchronized with the transition of the ionized particles. moving a current particle along a nearly circular path perpendicular to an axial magnetic field, causing the particle to make many transitions through a small number of electrode pairs, accelerating and increasing the radius with each transition Can be done.

(Problem to be Solved by the Invention) Conventional cyclotrons have a relativistic effect that increases the mass of the ion particles, causing them to move slower and out of period with the radio frequency excitation being applied to the electrodes. There are problems caused by

Particles can back up to the required speed and therefore
By increasing the magnetic field as the radius increases,
The period of the particles can be maintained for radio frequency excitation.

Therefore, this magnetic field is said to have the form of an isochronous magnetic field. However, because this magnetic field shape causes the ionized particle beam to lose focus, azimuthal changes or "flutter" are included in the magnetic field to refocus the particles.

Cyclotrons are typically constructed using resistive magnet coils housed within polar magnetic yokes, but the volume and weight of these magnets means that cyclotrons are housed in large buildings. Limited to use. Also, the amount of power supplied to the resistive coil requires a fairly large power supply.

Cyclotrons using superconducting magnets have been proposed, but they use ferromagnetic yokes, which add considerable volume and weight.

(Means for Solving the Problems) The present invention provides a cyclotron using a superconducting magnet without an iron yoke. The desired isochronous magnetic field variation in the radial direction and the desired variation of the magnetic field in the azimuthal direction are achieved with this cyclotron.

In accordance with the invention, a superconducting magnet having at least one cylindrical magnet coil is provided, the magnet coil being disposed within a cryostat to produce a magnetic field extending in the axial direction of the magnet, and the cryostat being transversely In a cyclotron, the superconducting magnet (2
9) constitutes a yokeless means for generating the magnetic field, and has interaction means (12 to 17) inside the axial chamber (26).
) are arranged, their interaction means interacting with said magnetic field to cause the axial magnetic field to "flutter" or fluctuate in an azimuthal direction with respect to said axis (11) and
resonant cavity means configured to vary the axial magnetic field isochronously in a radial direction from 1), and within the axial chamber (26), generating an electric field for accelerating a beam of ionized particles; (30, 31) are arranged, and the interaction means (1, 2-17) and the resonant cavity means (30° 31)
together form a beam space arranged radially from said axis (11), in which beam space a cyclotron is obtained in which said ionizing particle beam can be accelerated.

The interaction means (12-17) comprises sector-shaped ferromagnetic pole pieces, and the resonant cavity means (30°31) comprises sector-shaped members (32-37) inserted between the pole pieces. is preferred.

(Example) The present invention will be described in detail below with reference to the drawings.

The accelerating effect of the cyclotron is applied to the ionizing particle beam which is continuously injected into the center of the disc-shaped beam space 10.

An axial magnetic field extends parallel to the central axis 11 of the cyclotron (the beam space 10 extends radially outwards from this central axis 11) and, by interaction with interaction means in the form of soft iron pole pieces 12-17, the beam Subject to azimuthal and radial variations within a spatial domain. The axial magnetic field is
It is generated by yokeless means in the form of a superconducting magnet 29 having a set of superconducting magnet coils 21-24. Since the superconducting magnet coils 21 to 24 are housed inside the cylindrical cryostat 25, these coils are kept close to absolute zero due to their superconductivity. The low temperature holding device 25 forms a cylindrical chamber 26 extending in the axial direction from the center. low temperature storage bag ri
The details of the structure of 125 will be explained later.

Soft iron pole pieces are provided as three upper pole pieces placed at an angle of 120 degrees about axis 11 in chamber 26 . The lower soft iron poles 15.degree. 16.17 are also arranged within the chamber 26 at an angle of 120.degree. to each other about the axis 11. The lower pole piece 15 is axially aligned with the upper pole piece 12, and the other upper and lower pole pieces are similarly arranged. The shape, arrangement and magnetic properties of the pole pieces are configured and selected to provide the desired variation in axial magnetic field strength.

Figures 6 and 7 illustrate the azimuthal variation and isochronous radial shape of the magnetic field, respectively.

FIG. 6 shows the variation in magnetic field strength around the periphery of the cyclotron, with the positions of two of the pole pieces 12-17 shown at 80 degrees and 180 degrees. FIG. 7 shows the radial variation of the magnetic field from 3,5T at the axis 11 of the cyclotron to 3,6T at the periphery E. FIG.

Referring again to FIGS. 1-3, a radio frequency voltage for excitation of a particle beam rotating within beam space 10 is applied to radio frequency cavity means in the form of member 30.31 in chamber 26. Supplied via These members are 1
Upper fan extension 32 arranged at a 20 degree angle.
Contains 33.34. Their fan-shaped extensions are beam space 1
0 and radially outwardly from the shaft 11 and disposed between the pole pieces 12-14.

As shown in detail in FIG.
4 has a prismatic steel shell 39. This steel shell 39 is enclosed within another larger steel shell 40. The steel shells 39, 40 are spaced apart to form a narrow gap 41. A steel shell 40 is axially connected to an adjacent steel shell at the center 42 of the cyclotron and includes all extensions 32-32.
A gap 41 at No. 4 communicates with the center.

As shown in FIG. 2, each extension has two arms 41a, 41b extending generally radially outward from the axis 11 in a cross-section perpendicular to the axis 11, and a circumferential arm 41c. Appears as a fan-shaped hollow piece with.

The lower extensions 35, 36, 37 are similarly spaced about the axis 11 and similarly connected to each other in the center and are likewise arranged between the lower pole pieces inside the chamber 26.

Each extension 35-37 is axially aligned with one of the upper extensions.

As best shown in FIG.
34 axially faces each of the lower extensions 35 - 37 , the opposing extensions being axially separated to partially form the beam space 10 .

Similarly, pole pieces 13-14 axially face and are axially separated from lower pole pieces 15-17 to partially define beam space 10.

By interposing the resonant cavity members 32 to 37 in the circumferential direction between the magnetic pole pieces 12 to 17, the resonant cavities are extended in the axial direction as necessary to efficiently provide excitation radio frequency power. Can be done. In the illustrated example, the resonant cavity member is one quarter of the wavelength of the required radio frequency. The end of the cavity 41 remote from the beam space 10 is closed to form a quarter-wave resonator.

An excitation radio frequency voltage is supplied via coaxial cables 42 to 44 to the cavity 40 between the inner shell 39 and the outer shell 40 to generate a sinusoidal voltage between the ends of the cavity adjacent the beam space 10. Generates a large oscillating voltage.

The cavities of the upper and lower extensions are excited in phase, and in the example shown they have a
Radio frequencies with twice the frequency are supplied.

Please refer to FIG. This figure shows an axial section through the upper and lower extensions. The beams 50 proceed from left to right in the figure, and the excitation radio frequencies are synchronized to provide the necessary polarity to accelerate the particles through each cavity.

Each ionized particle passes through the two shells that make up each cavity, and the phase of the voltage applied to these shells is synchronized to provide an accelerating voltage to those particles, so that each particle has an acceleration voltage per revolution. Six acceleration voltages are applied. Each accelerating voltage is typically 30 KV and the ion rotation frequency is 5.
It is 0MHz. That is, each orbit has an energy of 18
It is increased by 0 KV and the cavity frequency is 150 MHz. Once the particles have achieved the required energy state, they are ejected from the cyclotron.

As shown in FIG. 8, when negative ions are used, the beam 80
The ions are made to strike the thin carbon foil 60 at appropriate points within the helical path.

The foil 60 removes negative charge from the ions, making them positive ions. The ions therefore exit the cyclotron through the extraction tube 61 as they are deflected by the axial magnetic field and travel radially outward. The coil can have any number of alternative positions depending on the energy required for the output particles. Therefore, by changing the position of the foil, 10 M e V and 17 M e
Different outputs of V can be obtained.

The ion flow is provided by an ion source 70 located at the top of the cyclotron. The ion source emits a stream of negative ions radially outward. The ion stream is bent 90 degrees by the magnetic field, at which point the differential vacuum pump pumps out much of the hydrogen gas. A device that easily removes gas from the ion stream and a device that evacuates the beam space very efficiently makes the overall efficiency of the cyclotron very high.

The negative ion stream 71 from the ion source 70 is immediately bent 90 degrees to be directed along the central axis 11 and passes through the hole 72 provided at the top of the resonant cavity members 32-34 into the beam space 10. Go inside.

As shown in FIG. 1, the ion stream is again bent 90 degrees, as indicated by reference numeral 79, and begins orbiting within beam space 10.

FIG. 4 shows a cyclotron very similar to the cyclotron shown in FIG. In this example, an ion generator is located at location 74 within beam space 10 and a stream of ions is provided through tube 73 from an ion supplier 75 . The ion stream exits through a hole in tube 73 in ion generator 74 .

In both cyclotrons, the ion stream is directed to the center of the beam space 10. At the center of the beam space, the ion streams begin their spiral orbital motion.

In the embodiment shown in FIGS. 3 and 4, the illustrated ion source can supply positive or negative ions. When positive ions are used, the extraction foil shown in FIG. 8 cannot be used, and the accelerated ions are extracted with the structure shown in FIG. 9.

In FIG. 9, when the ion stream 80 reaches the outer orbit,
The ion stream enters the field of changing magnetic field 70. The magnetic field deflects the ion stream to a slightly different trajectory 80a, forcing the in-stream into an electrostatic deflector 76, which causes the ion stream to enter another changing magnetic field 76 that brings the cyclotron into contact. Try to put it out in the direction.

Alternatively, a target (actually a workpiece) can be placed in the path of the ion stream within beam space 10 so that the ions directly impinge on the target.

There is no ferromagnetic material inside the circumferential space between the sector-shaped iron pole pieces 12-14 and 15-17, so that no ferromagnetic material is present due to the interaction between the main magnetic field and the pole pieces. It is possible to cause large amplitude azimuthal magnetic field fluctuations.

Furthermore, by placing radio frequency cavities within these spaces, the cavities can be made more efficient, and a much larger number of cavities can be provided than previously possible. The acceleration per turn of the spiral path of ionized particles can be increased.

In addition, the inner shell 39 of each cavity extension is hollow and open at the top and bottom, so that the beam space 10 and the vacuum pump 55
A low impedance axially extending path with nothing in between is formed. A vacuum pump 55 is attached to a plate 56 that closes off the upper end of the chamber 26. The lower end of the chamber 26 is closed off by a plate 57.

In this way, the cyclotron can be constructed without an iron yoke, making it extremely lightweight and portable. This cyclotron is highly suitable for neutron radiography and neutron therapy.

Next, the low temperature maintenance device 25 will be explained. Four cylindrical magnet coils 21゜22.23.24 of low temperature maintenance device 25
is attached to a cylindrical frame 35.

The frame 35 includes a cylindrical shell 36 and an end plate 37. 38 to form a liquid helium bath. This liquid helium bath
A port 39 for injecting liquid helium is provided so that the coils 21 to 24 operate immersed in liquid helium.

Reed was also passed on that day at 39.

Also housed within the cryostat 25 is a radiation shield 43 and a double-walled container 44 containing a liquid nitrogen bath 44a. container 4
4 is supported by arms 48 from the top plate 45 and bottom plate 46 of the cryostat, and the helium bath is supported from arms 47. All its supports are made of poor conductors of heat.

The inner cylindrical wall 51 and the outer cylindrical wall 52 of the cryostat together with the top plate 54 and the bottom plate 55 form a vacuum chamber. This vacuum chamber is evacuated to resist heat ingress.

The cryostat follows modern standard construction for high-performance superconducting magnets, in which the coil is kept near absolute zero inside a liquid helium bath, while the rest of the structure is kept out of heat. This minimizes helium and nitrogen replenishment.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the cyclotron of the present invention, Fig. 2 is a transverse sectional view taken away from the beam space of the cyclotron of Fig. 1, and Fig. 3 is a perspective view showing a part of the cyclotron of Fig. 1 cut away. Figure 4 is a partially cutaway perspective view of another cyclotron similar to the cyclotron shown in Figure 3, Figure 5 is a developed view of the resonant cavity of the cyclotron in Figure 1, and Figure 6 is Graph showing variations in the azimuthal direction of the magnetic field, seventh
8 is a cross-sectional view of the cyclotron showing the output beam; and FIG. 9 is a cross-sectional view similar to FIG. 8 showing an alternative output configuration. 10...Beam space, 12-17...Magnetic pole piece, 21
~24...Coil, 25...Low temperature maintenance device, 26.
...Chamber, 30.31...Resonance cavity, 32.37...
Extension member, 39.40... steel shell, 60... carbon foil,
70...Ion source. Applicant's agent Sato -Engraving of the side (no change in content) Document P of drawings (no change in content) ~・6・hri・Z

Claims (1)

[Claims] 1. A superconducting magnet having at least one cylindrical magnet coil, the magnet coil being arranged inside a cryostat to generate a magnetic field extending in the axial direction of the magnet, in a cyclotron in which the holding device forms an axial chamber of approximately circular cross-section and contains said magnetic field in said axial chamber, said superconducting magnet (29) constituting a yokeless means for generating said magnetic field; Interacting means (12-17) are arranged within said axial chamber (26), said interacting means interacting with said magnetic field to generate an axial magnetic field in an azimuthal direction with respect to said axis (11). A beam of ionized particles is arranged to "flutter" or fluctuate and vary the axial magnetic field isochronously in a radial direction from the axis (11); A resonant cavity means (
30, 31) are arranged, and the interaction means (12-1
7) and said resonant cavity means (30, 31) are connected to said shaft (11).
) together form a radially arranged beam space in which said ionizing particle beam can be accelerated. 2. The cyclotron according to claim 1, wherein the interaction means (12-17) comprises sector-shaped ferromagnetic pole pieces, and the resonant cavity means (30, 31) are arranged between the pole pieces. A cyclotron comprising fan-shaped members (32 to 37) inserted into the cyclotron. 3. In the cyclotron according to claim 2, the resonant cavity means (30, 31) extend in the axial direction to a length that allows highly efficient resonance to be performed for acceleration excitation. A cyclotron characterized by: 4. In the cyclotron according to claim 1, the flow of ionized particles is directed along the magnetic field into the beam space (1).
Cyclotron characterized in that it is provided with means (70) for axially injecting into the cyclotron (0). 5. A cycloton according to claim 4, wherein the means (70) comprise a negative ion generator configured to inject a stream of negative ions into the interior of the beam space (10), A cyclotron characterized in that a stripper foil (60) is provided for extracting the ions. 6. A cyclotron according to claim 1, characterized in that means (74, 75) are provided for directly injecting a stream of ionized particles into the interior of the beam space (10). 7. A cyclotron according to claim 5, wherein the means (70) comprises a positive ion generator (73-75) and a weakened magnetic field region (75) is provided for extracting the excited ions. A cyclotron characterized by: 8. In the cyclotron according to claim 2, the resonant cavity means (32 to 37) are arranged in the beam space (1).
A cyclotron characterized in that it has a hollow interior space communicating with a vacuum pump (55) and a vacuum pump (55). 9. In the cyclotron according to claim 2, the radial boundary of the ferromagnetic pole pieces (12 to 17) is a straight radial line, a spiral shape, or a combination of both. A cyclotron characterized by being a trait. 10. In the cyclomethron according to claim 2, the radial boundary of the resonant cavity means (32-37) is a straight radial line, a spiral, or a combination of both shapes. A cyclotron characterized by: