JP2001216908A - Ion source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly cool a plasma chamber, thereby preventing demagnetization of a permanent magnet due to heating of mirror coils. SOLUTION: In an ion source where by mirror coils 12 and permanent magnets 14 arranged on the outside of a plasma chamber 16, a mirror magnetic field is generated, plasma is confined into the plasma chamber 16 and ions are generated from the chamber, a thin cooling jacket 50 is arranged between the mirror coils and the permanent magnets.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a mirror coil and a permanent magnet disposed outside a plasma chamber to generate a mirror magnetic field, to confine plasma in the plasma chamber, and to generate ions therefrom. The present invention relates to an ion source, and more particularly, to an ion source capable of uniformly cooling a plasma chamber and preventing demagnetization of a permanent magnet due to heat of a mirror coil.

[0002]

2. Description of the Related Art FIG. 1 shows an example of the configuration of an electron cyclotron resonance (ECR) ion source used in a heavy ion beam cancer treatment apparatus and the like described in Japanese Patent Application Laid-Open No. 9-161688. In the figure, 10 is a cylindrical yoke, 12
Are mirror coils provided on the left and right in the yoke 10 for generating a mirror magnetic field, and 14 is a mirror coil 12
A six-pole permanent magnet 16 serving as a cusp magnet for generating a cusp magnetic field is provided inside the six-pole permanent magnet 14. This is a plasma chamber.
Inside, the plasma is confined by the combined magnetic field formed by the mirror magnetic field and the cusp magnetic field.

[0003] Reference numeral 30 denotes a gas introduction pipe which is disposed on the central axis CL of the ECR ion source and supplies a material gas into the plasma chamber 16, and 32 denotes a microwave for irradiating the gas in the gas introduction pipe 20. The supply waveguide 34 is a screen electrode forming the wall surface of the plasma chamber 16, 36.
Is an extraction electrode which is disposed on the same axis as the screen electrode 34 and holds a ground level potential.

In the ECR ion source having such a configuration, an EC positioned by the mirror magnetic field of the mirror coil 12 is used.
When the microwave from the waveguide 32 acts on the gas in the gas introduction tube 30 passing through the first-stage ECR zone 40 indicated by the broken line, which is the R magnetic field, the frequency of the microwave for accelerating the electrons and the mirror coil 12 When the rotation periods of the electrons by the mirror magnetic field coincide with each other, the electrons undergo cyclotron resonance and are accelerated while rotating around the magnetic flux of the mirror magnetic field. When the ECR-accelerated electrons collide with gas molecules and atoms in the gas inlet tube 30, ionization of the gas occurs, and the electrons are turned into plasma to generate electrons and positive ions. Of these, positive ions have a large mass, and most of them
Although stagnating in zero, the electrons diffuse into the plasma chamber 16 along the magnetic flux of the mirror magnetic field.

On the other hand, electrons supplied from the gas inlet tube 30 are ECR-accelerated in the plasma chamber 16 by the microwave from the waveguide 32 and the combined magnetic field of the hexapole permanent magnet 14 and the mirror coil 12. The electrons collide with a non-ionized gas introduced into the plasma chamber 16 to generate plasmanized electrons and positive ions. Further, the electrons collide with the positive ions and multiply-charged ions are sequentially ionized to generate polyvalent ions. Generated. The ECR acceleration of electrons is performed in a closed hollow cylindrical second-stage ECR zone 42 formed by a combined magnetic field of the hexapole permanent magnet 14 and the mirror coil 12. Becomes high energy. Therefore, when electrons and gas collide in the second-stage ECR zone 42, ionization collision occurs most frequently, and many plasma ions are generated. For this reason,
In the plasma chamber 16, an electron potential distribution having an ion peak at the central axis of the second-stage ECR zone 42 occurs, and positive ions generated in the second-stage ECR zone 42 are most likely to be located on the central axis of the second-stage ECR zone 42. Many are trapped.

[0006] High-energy electrons accelerated by ECR in the second-stage ECR zone 42 repeatedly collide with positive ions confined on the central axis of the second-stage ECR zone 42, so that multiply-charged ions due to sequential ionization are obtained. Is generated. Since the plasma chamber 16 and the hexapole permanent magnet 14 are maintained at a positive high voltage and the extraction electrode 36 is maintained at the ground-level potential, the multiply-charged ions are generated by the hexapole permanent magnet 14 and the plasma chamber 16. Due to the action of the electric field between the plasma chamber 16 and the extraction electrode 36, the plasma is extracted from the plasma chamber 16 to the outside through the extraction electrode 36.

As described above, in the ECR ion source, high-temperature plasma is contained in the plasma chamber 16 and ions are generated therefrom. However, since the six-pole permanent magnet 14 outside the plasma chamber 16 is demagnetized when exposed to a high temperature, the chamber 16 needs to be cooled, and water cooling with cooling water is generally performed.

[0008]

Conventionally, however, no cooling mechanism has been provided between the mirror coil 12 and the six-pole permanent magnet 14. Therefore, the mirror coil 1
Due to the heat generated in No. 2, the six-pole permanent magnet 14 was exposed to a high temperature, and could be demagnetized.

The present invention has been made to solve the above-mentioned conventional problems, and has as its object to prevent demagnetization of a permanent magnet due to heat generation of a mirror coil.

[0010]

According to the present invention, a mirror magnetic field is generated by a mirror coil and a permanent magnet disposed outside a plasma chamber, and plasma is confined in the plasma chamber and ions are generated therefrom. In the ion source described above, the above problem is solved by disposing a thin cooling jacket between the mirror coil and the permanent magnet.

[0011] Further, at least one of an inner sleeve that covers the outer periphery of the permanent magnet, the outer sleeve that fits with the inner sleeve, and an outer peripheral surface of the inner sleeve or an outer peripheral surface of the outer sleeve. At least one of an inner cover that covers an end surface of the permanent magnet, an outer cover that is in close contact with the inner cover, and an outer surface of the inner cover or an inner surface of the outer cover. And a cover-side cooling liquid passage formed in the cooling device, the cooling jacket is made thin, and the ion source can be made compact.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In this embodiment, as shown in FIG. 2, in the same ECR ion source as the conventional example shown in FIG. 1, a thin cylindrical member is provided between a central hexapole permanent magnet 14 and mirror coils 12 on both sides. The water-cooled jacket 50 is disposed.

The water-cooled jacket 50 is shown in FIG. 3 (a front view of a state in which a portion in front of the outer sleeve is cut away), FIG.
(Partial cross-sectional view along line IV-IV in FIG. 3), FIG. 5 (also cross-sectional view along line VV), FIG. 6 (also cross-sectional view along line VI-VI), FIG. 6 (illustrated in section VII), FIG. 8 (also enlarged in section VIII), and FIG. 9 (cross-sectional view taken along line IX-IX in FIG. 3). A sleeve 52, an outer sleeve 54 fitted with the inner sleeve 52,
2, two double-threaded grooves 56 formed on the outer peripheral surface
A, 56B, a sleeve-side cooling water passage 56, a disc-shaped inner cover 58 covering the end face of the six-pole permanent magnet 14, for example, and the same disc-shaped outer cover tightly attached to the inner cover 58 60 and a cooling water inlet 62C and an outlet 62D formed on the outer surface of the inner cover 58, for example.
Are respectively formed in the grooves 56 of the sleeve side cooling water passage 56.
A cooling water is supplied to a cover-side cooling water passage 62 formed of a groove 62A that communicates with end points 56C and 56D of the sleeve-side cooling water passage 56A and 56B. The cooling water supply pipe 64 and the cooling water discharge pipe 66 for feeding and discharging are configured.

The inner sleeve 52 is a thin cylinder,
Grooves 56A and 56B of a shallow and wide sleeve-side cooling water passage 56 are cut in the inner sleeve 52 in the form of a double thread. The grooves 56A, 56B of the sleeve-side cooling water passage 56
One end 56C, 56D is connected to an inner cover 58, which is also cut by a shallow and wide groove 62A. The inner cover 58 connects two double-threaded grooves 56A, 56B. The inner sleeve 52 and the inner cover 58 are covered with a thin cylindrical outer sleeve 54 and a thin disk-shaped outer cover 60 so as to cover the entire sleeve along the convex portion between the grooves. For example, it is fixed watertight by brazing or welding. The outer sleeve 54 has holes 54A and 54B (FIG. 4) for connecting the cooling water introduction pipe 64 and the cooling water discharge pipe 66. In FIG. 7 and FIG. 8, 68 is likely to occur.

The operation will be described below.

The cooling water introduced from the cooling water introducing pipe 64 is supplied to one of the grooves 56 of the double threaded cooling water passage 56 of the inner sleeve 52 through the hole 54A on one side of the outer sleeve 54.
A, and flows toward the tip (right side in FIG. 3). An inner cover 58 is connected to the end of the groove, and a groove 62 of a cover-side cooling water passage 62 formed in the inner cover 58 is formed.
Since the grooves 56A and 56B are connected via A,
Here, the other groove 5 of the cooling water passage 56 of the inner sleeve 52
Flow into 6B. In this way, the cooling water flowing in the opposite direction to the groove 56A on the entry side is applied to the holes 5 formed in the outer sleeve 54.
4B comes out to the cooling water discharge pipe 66.

In this embodiment, since the water cooling jacket is made thin by making the water channel thin, the ion source can be made compact. At this time, since the water channel is widened and arranged almost uniformly in the water-cooled jacket, the plasma chamber can be uniformly cooled, and the demagnetization due to the heat of the six-pole permanent magnet can be reliably prevented.

In this embodiment, since the sleeve-side cooling water passage 56 is formed on the outer surface of the inner sleeve 52, the processing is easy. The position where the sleeve-side cooling water passage 56 is formed is not limited to this, and may be formed on the inner surface of the outer sleeve 54. Further, the formation position of the cover-side cooling water passage 62 is not limited to the outer surface of the inner cover 58 but may be formed on the inner surface of the outer cover 60. Further, cooling water passages may be provided in both the inner sleeve and the outer sleeve, or provided in both the inner cover and the outer cover to increase the flow rate of the cooling water. The type of the cooling liquid is not limited to water.

In the above embodiment, the present invention relates to
Although applied to the R ion source, the scope of the present invention is not limited to this. Further, the type of the permanent magnet is not limited to the six-pole permanent magnet.

[0021]

According to the present invention, it is possible to prevent the permanent magnet from being demagnetized due to the heat generated by the mirror coil.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the overall configuration of a conventional ECR ion source.

FIG. 2 is a cross-sectional view showing the overall configuration of the embodiment of the present invention.

FIG. 3 is a front view showing a configuration of a water-cooling jacket used in the embodiment and showing a state in which a portion in front of an outer sleeve is cut away.

FIG. 4 is a partial cross-sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a cross-sectional view along the line VV.

FIG. 6 is a cross-sectional view along the line VI-VI.

FIG. 7 is an enlarged view of a portion VII in FIG. 6;

FIG. 8 is an enlarged view of the same section VIII.

9 is a cross-sectional view taken along line IX-IX of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Mirror coil 14 ... Six-pole permanent magnet 16 ... Plasma chamber 50 ... Water cooling jacket 52 ... Inner sleeve 54 ... Outer sleeve 56 ... Sleeve side cooling water passage 58 ... Inner cover 60 ... Outer cover 62 ... Cover side cooling water passage 64 ... Cooling water inlet pipe 66 ... Cooling water discharge pipe

Claims (2)

[Claims] 1. An ion source in which a mirror magnetic field is generated by a mirror coil and a permanent magnet disposed outside a plasma chamber, plasma is confined in the plasma chamber, and ions are generated therefrom. An ion source having a thin cooling jacket disposed between a coil and a permanent magnet. 2. The outer sleeve according to claim 1, wherein the cooling jacket comprises: an inner sleeve that covers the outer periphery of the permanent magnet; an outer sleeve that fits the inner sleeve; and an outer peripheral surface of the inner sleeve or an outer peripheral surface of the outer sleeve. A sleeve-side coolant passage formed in at least one of the following: an inner cover that covers an end face of the permanent magnet; an outer cover that is in close contact with the inner cover; and an outer surface of the inner cover or an inner surface of the outer cover. An ion source, comprising: a cover-side coolant passage formed in at least one of the following.