JP6952997B2 - Mirror magnetic field generator and ECR ion source device - Google Patents

Description

The present invention relates to a mirror magnetic field generator for plasma confinement for an electron cyclotron resonance heating type ion source (ECR ion source) that generates high-energy ions, and an ECR ion source device using the same. The present invention is used, for example, as a mirror magnetic field generator for a medical accelerator, a semiconductor manufacturing apparatus, an experimental linear accelerator such as a linear collider, and an ion source apparatus.

Conventionally, in an ECR ion source, a high-frequency electromagnetic field having an electron cyclotron resonance frequency proportional to the magnetic field strength is applied to a dilute gas in a static magnetic field to turn it into plasma, and the electrons in the plasma are converted into an electron cyclotron resonance (ECR: electron-cyclotron). -resonance) can accelerate to high energy and increase the efficiency of ionization.

At this time, if the volume of the space satisfying the resonance condition (ECR space) can be increased, the amount of ions generated increases, but in order to satisfy the resonance condition, the magnetic field must be uniform.

On the other hand, the ECR ion source forms a magnetic field by using a solenoid coil, a permanent magnet, or the like, and restricts the movement of the charged particles in the plasma in a direction orthogonal to the magnetic field to confine the charged particles. Regarding the motion parallel to the magnetic field, confinement is realized by forming a so-called mirror magnetic field and repelling charged particles there by narrowing the magnetic flux lines at both ends in the magnetic field direction of the confinement space to raise the magnetic field.

For example, Patent Documents 1 and 2 show a device for forming a mirror magnetic field by two annular permanent magnets. Each of these devices is also used with an auxiliary permanent magnet for increasing or adjusting the strength of the magnetic field.

Further, Patent Document 3 discloses a device for forming a mirror magnetic field by passing an electric current through two annular coils in the same direction.

Non-Patent Documents 1 and 2 show an ECR ion source device using a mirror magnetic field formed by a permanent magnet.

Japanese Unexamined Patent Publication No. 8-64392 Japanese Unexamined Patent Publication No. 2006-49020 JP-A-2002-313788

Y.Iwashita, H.Tongu, Y.Fuwa, and M.Ichikawa "Compact permanent magnet H + ECR ion source with pulse gas valve", REVIEW OF SCIENTIFIC INSTRUMENTS 87, 02A718 (2016) Y.Liu, GDAton, H.Bilheux, JMCole, FWMeyer, GDMills, CAReed, CLWilliams, "INITIANL PERFORMANCE OF A 6GHZ" VOLUME "ECR ION SOURCE", Proceedlings of the 2003 Particle Acceleratou Conference pp 998- 1000

In the mirror magnetic field generator, when the mirror magnetic field is increased, the uniformity of the magnetic field in the central space is disturbed, which reduces the volume of the ECR space. Therefore, the confinement efficiency and the generation efficiency of plasma conflict with each other. It has been reported that the peak value of the mirror magnetic field should be about twice the magnetic field in the ECR space (ECR magnetic field).

In a conventional mirror magnetic field generator, each mirror magnetic field region located at both ends of the plasma generation space in the magnetic field direction has a single pole.

For example, in Patent Document 1, the mirror magnetic field regions at both ends of the plasma generation chamber have a single pole due to the main annular permanent magnet, Patent Document 2 has a single pole due to the annular permanent magnet, and Patent Document 3 has the coil. It has a single pole due to the central space.

Further, in Non-Patent Document 1, the mirror magnetic field regions at both ends of the plasma generation chamber (plasma chamber) have a single pole due to the wall of the magnetic material. Non-Patent Document 2 has a single pole due to the wall or space forming the end face of the plasma generation chamber.

As described above, since all the conventional mirror magnetic field generators have a single pole at both ends of the mirror magnetic field, all the magnetic field lines of the mirror magnetic field are focused on the single pole. Then, the distance in the magnetic field direction required for all the magnetic field lines to converge becomes longer, and the length in the magnetic field direction of the uniform space of the magnetic field, that is, the space satisfying the resonance condition (ECR space) becomes shorter by that amount.

If the plasma generation space has a cylindrical shape, in the case of a single pole, the region where the magnetic field changes at the end of the mirror magnetic field becomes as large as the radius of the cylinder, which greatly limits the size of the ECR space. It is supposed to be.

The present invention has been made in view of the above problems, and an object of the present invention is to increase the volume of the ECR space and improve the plasma generation efficiency in a mirror magnetic field generator applied to an ECR ion source.

The mirror magnetic field generator according to the present invention is a mirror magnetic field generator applied to an ECR ion source and for generating a mirror magnetic field in which charged particles are confined in a plasma generation space by a main magnetic field generation member, and is the plasma generation space. On the end side in the magnetic field direction in the above, a plurality of magnetic force focusing members for dispersing the magnetic field lines on the end side in the mirror magnetic field and focusing the dispersed magnetic field lines are arranged.

The magnetic field lines on the end side in the mirror magnetic field are dispersed by the plurality of magnetic field focusing members, and the dispersed magnetic field lines are focused by each magnetic field focusing member, and a small mirror magnetic field is formed here. Since the region where one magnetic force focusing member performs focusing is reduced and the region where the magnetic field changes is reduced, the distance in the magnetic field direction (Z-axis direction) required for focusing is shortened. The peak value of the local magnetic field generated by each magnetic force focusing member can be about the same as before dispersion, and the degree of confinement of charged particles by the mirror magnetic field can be about the same.

Preferably, the magnetic force focusing member comprises a columnar permanent magnet having magnetic poles formed in the direction of the magnetic field. Further, the magnetic force focusing member may be made of a columnar soft magnetic material. Further, the magnetic field focusing member may consist of two sets of coils that are wound concentrically around the magnetic field direction and generate a magnetic field that draws the magnetic field lines of the mirror magnetic field by passing currents in opposite directions. ..

For example, the magnetic force focusing members are arranged so as to be spaced apart from each other along the circumferential direction of a plurality of concentric circles.

Preferably, the magnetic field focusing member is arranged inside the plasma generation space with respect to a yoke arranged on the end side to form the mirror magnetic field, and the end in the mirror magnetic field formed by the yoke. Disperse the magnetic field lines on the part side.

The ECR ion source device according to the present invention includes a mirror magnetic field generator, a gas supply means for supplying gas to the plasma generation space, a microwave introduction means for introducing microwaves into the plasma generation space, and the plasma generation space. It is provided with an extraction means for extracting the ions generated in the above.

The mirror magnetic field forming method according to the present invention is applied to an ECR ion source, and is a mirror magnetic field generating method for generating a mirror magnetic field in which charged particles are confined in a plasma generation space by a main magnetic field generating member, and is the plasma generation space. A plurality of magnetic force focusing members for dispersing and focusing the dispersed magnetic field lines in the mirror magnetic field are arranged on the end side in the magnetic field direction, and the plasma generation space is provided by the plurality of magnetic force focusing members. Form multiple small mirror magnetic fields within.

According to the present invention, in the mirror magnetic field generator applied to the ECR ion source, the volume of the ECR space can be increased and the plasma generation efficiency can be improved.

It is a figure which shows the example of the schematic structure of the mirror magnetic field generator of this invention. It is a figure which looked at the left-right side surface of the plasma generation space of the mirror magnetic field generator of FIG. It is a figure which shows the example of the magnetic flux distribution of a mirror magnetic field. It is a figure which shows the example of the shape of the magnetic force focusing member. It is a figure which shows another example of the schematic structure in the mirror magnetic field generator of this invention. It is a figure which shows the example of the structure of the magnetic field focusing member of the mirror magnetic field generator of FIG. It is a figure which shows the ECR ion source apparatus of one Embodiment of this invention. It is a figure which shows the shape of the upstream cover member. It is a figure which shows the shape of the downstream cover member. It is a figure which shows the example of the magnetic flux distribution in the ECR ion source apparatus of one Embodiment. It is a figure which shows the example of the magnetic flux distribution in the vicinity of the magnetic force focusing member on the extraction side. It is a figure which shows the example of the magnetic flux distribution when a coil is used as a magnetic force focusing member.

[Basic configuration of mirror magnetic field generator]
The basic configuration of the mirror magnetic field generator of the present invention will be described with reference to the example shown in FIG.

FIG. 1 shows an example of a schematic configuration of the mirror magnetic field generator 3, and FIG. 2 shows a view of the inner surface of the mirror magnetic field generator 3 of FIG. 1 in the left-right direction in the plasma generation space 100. There is.

In FIGS. 1 and 2, the mirror magnetic field generator 3 is applied to an ECR ion source to generate a mirror magnetic field in which charged particles are confined in the plasma generation space (plasma chamber) 100 by a main magnetic field generating member.

A plurality of magnetic force focusing members 20 and 21 for dispersing the magnetic field lines on the end side in the mirror magnetic field and focusing the dispersed magnetic field lines are arranged on both ends in the magnetic field direction in the plasma generation space 100.

That is, the mirror magnetic field generator 3 includes annular permanent magnets 11, 12, yokes 13, 14, 15, and a plurality of magnetic field focusing members 20, 21, which are main magnetic field generating members.

The permanent magnets 11 and 12 are magnetized in the radial direction, respectively. The permanent magnet 11 on the upstream side has N on the inner diameter side and S on the outer diameter side, and the permanent magnet 12 on the downstream side has the opposite.

The yokes 13, 14 and 15 are made of a soft magnetic material such as iron or a silicon steel plate, and the magnetic flux distribution by the permanent magnets 11 and 12 is adjusted to apply a strong uniform magnetic field of about several kilogauss to the plasma generation space 100 as a mirror magnetic field. Form. The yoke 13 is provided with an introduction port 13a for introducing gas and microwaves of about 2 to 8 GHz. The yoke 14 is provided with an extraction port 14a for extracting (deriving) the generated ions. The yoke 15 strengthens the magnetic field to the plasma generation space 100 and prevents magnetic flux leakage to the outside.

The magnetic force focusing members 20 and 21 are arranged inside the plasma generation space 100 with respect to the yokes 13 and 14 arranged on the end side for forming the mirror magnetic field, and are formed by the yokes 13 and 14. The magnetic field lines on the end side of the mirror magnetic field are dispersed.

The shapes, arrangements, materials, numbers, magnetizing directions, etc. of the permanent magnets 11 and 12 and the yokes 13, 14 and 15 shown here are examples, and are appropriately determined according to the ECR conditions (resonance conditions) and the specifications of the device. You can select it. For example, the arrangement can be changed in various ways, such as bringing the yoke 13 into contact with the magnetic force focusing member 20, separating the yoke 14 from the magnetic force focusing member 21, and separating the yoke 15 from the permanent magnet 11.
[Magnetic focusing member with permanent magnet]
The magnetic focusing members 20 and 21 are each composed of columnar permanent magnets 20a and 21a having magnetic poles formed in the direction of the magnetic field. As the permanent magnets 20a and 21a, permanent magnets made of various materials such as alloy magnets containing iron as a main component, ferrite magnets, and rare earth magnets such as samarium-cobalt magnets and neodymium magnets can be used.

In order to prevent demagnetization due to heat from the plasma, it is effective to embed these permanent magnets in a cover member made of a ceramic material as described later so as not to be directly exposed to the plasma. When the demand for heat resistance is high, it is effective to use a samarium-cobalt magnet.

The plurality of permanent magnets 20a and 21a are arranged at equal intervals with each other along the circumferential direction of the plurality of concentric circles.

That is, as shown in FIG. 2, the plurality of permanent magnets 20a and 21a are arranged along the circumferences of two circles, an inner small circle and an outer great circle, respectively. The number of permanent magnets 20a and 21a arranged on the outer circumference is larger than that on the inner circumference, and the intervals between the permanent magnets 20a and 21a are almost equal.

Further, the respective tip surfaces of the plurality of permanent magnets 20a and 21a, that is, the tip surfaces of the plurality of permanent magnets 20a or the tip surfaces of the plurality of permanent magnets 21a are on the same plane. That is, for example, the respective tip surfaces of the plurality of permanent magnets 20a are at the same position in the Z-axis direction, thereby forming a single plane perpendicular to the Z-axis. Further, there is no other magnetic material or coil that affects the magnetic field inside the plasma generation space 100 from this plane. That is, the yokes 13, 14 and the like are outside the permanent magnets 20a and 21a, and it is the permanent magnets 20a and 21a that are magnetic focusing members that finally control the mirror magnetic field.

As described above, in the mirror magnetic field generator 3, the mirror magnetic field regions located at both ends of the plasma generation space 100 in the magnetic field direction have a plurality of poles. The number of poles is equal to the number of permanent magnets 20a and 21a, respectively.

Although the plurality of permanent magnets 20a and 21a are arranged along the circumferential direction of the two circles here, they may be arranged along the circumferential direction of one or three or more circles. Alternatively, the permanent magnets 20a and 21a may be arranged radially or in a matrix.

The number of permanent magnets 20a and 21a may be, for example, about 10 to 50, and may be changed according to the area of the end face of the plasma generation space 100. The number and arrangement of the permanent magnets 20a and the permanent magnets 21a may be different, but may be the same.

Members necessary for plasma generation, such as an exhaust device for creating a vacuum in the plasma generation space 100, are appropriately used.

FIG. 3 shows an example of the magnetic flux distribution of the mirror magnetic field in the plasma generation space 100 of the mirror magnetic field generator 3.

As shown in FIG. 3A, in the mirror magnetic field in the plasma generation space 100, the entire magnetic field lines (magnetic flux) in the mirror magnetic field are dispersed by the plurality of permanent magnets 20a and 21a arranged at both ends, and each of them. The amount of magnetic field lines (magnetic flux) entering the permanent magnets 20a and 21a is reduced to one-third of the number. The magnetic field lines (magnetic flux) of the dispersed portion are focused by the permanent magnets 20a and 21a, respectively.

Since the respective permanent magnets 20a and 21a focus the magnetic field lines, the region where one permanent magnet 20a and 21a focuses is reduced, the region where the magnetic field changes is reduced, and therefore the magnetic field direction (Z-axis direction) required for focusing is reduced. The distance of is shortened. Therefore, the length of the uniform region of the magnetic field, that is, the space satisfying the ECR condition (ECR space) in the magnetic field direction becomes long.

The peak value of the local magnetic field generated by each of the permanent magnets 20a and 21a can be the same as before the dispersion by the plurality of permanent magnets 20a and 21a, and the degree of confinement of the charged particles in the mirror magnetic field is the same. Can be a degree. That is, by locally generating a magnetic field having a peak value of, for example, about twice that of the ECR space in the vicinity of the permanent magnets 20a and 21a, a sufficient confinement effect by the mirror magnetic field can be obtained.

That is, in the mirror magnetic field generator 3, the plurality of permanent magnets 20a and 21a arranged at both ends form poles at the ends of the mirror magnetic field, and the number of small permanent magnets 20a and 21a is the same as the number of the permanent magnets 20a and 21a. It can be said that a mirror magnetic field was formed. In this sense, it can be said that the mirror magnetic field generator 3 is a multi-mirror magnetic field system (multi-mirror system).

That is, the mirror magnetic field generator 3 has the same number of poles as the number of the permanent magnets 20a and 21a at both ends of the plasma generation space 100. In this respect, in contrast to the conventional mirror magnetic field generator "having a single pole", the mirror magnetic field generator 3 described here "has a large number of poles", which is the mirror magnetic field generator 3. It is a big feature.

As shown in FIG. 3B, the magnetic field in the plasma generation space 100 has strong peaks at both ends where the permanent magnets 20a and 21a are arranged, and has a flat uniform magnetic field about half of that in the central portion. Become. Assuming that the length of the mirror region EM in the plasma generation space 100 in the Z-axis direction is EM1, the length of the ECR space EE with a uniform magnetic field is EE1, which is the length of the ECR space EE as compared with the length EM1 of the mirror region EM. The length EE1 is sufficiently secured without being significantly reduced.

The radial size of the ECR space EE does not change depending on the provision of the permanent magnets 20a and 21a. Therefore, by providing the permanent magnets 20a and 21a, the ECR space 100 can be used in the limited plasma generation space 100. The volume of EE can be increased. Thereby, the plasma generation efficiency can be improved.

Therefore, when the ECR ion source device is configured by using the mirror magnetic field generator 3, the amount of ions extracted from the ECR ion source device, that is, the withdrawal current can be increased efficiently.

FIG. 4 shows an example of the shape of the magnetic force focusing member.

The magnetic force focusing member 20a of FIG. 4A has a columnar shape. Its dimensions largely depend on the size of the plasma generation space 100. For example, when the plasma generation space 100 is columnar and has a diameter and a length of 34 mm, the magnetic force focusing member 20a has a diameter of 2 to 2. It is about 5 mm and has a length of about 2 to 5 mm. For example, it has a diameter of 3 mm and a length of 3 mm. Dimensions other than these may be used. The ratio of the diameter to the length of the cylinder can be, for example, 1: 1, 1: 1.5, 1: 2, or any other ratio.

The magnetic force focusing member 20b of FIG. 4B has a hexagonal columnar shape. The magnetic force focusing member 20c of FIG. 4C has a cannonball shape. The tip of the magnetic force focusing member 20d shown in FIG. 4D has a conical shape.

In addition to these shapes, it is possible to form a combination of these shapes and various other shapes.
[Magnetic force focusing member made of soft magnetic material]
In the above-mentioned example, the example in which the permanent magnets 20a and 21a are used as the magnetic focusing members 20 and 21 has been described, but a soft magnetic material may be used instead of the permanent magnets 20a and 21a.

That is, the magnetic force focusing members 20 and 21 may be configured by using a columnar soft magnetic material. The soft magnetic material has a small holding force and a large magnetic permeability. For example, iron, silicon steel, permendur and the like. Permendur has a high saturation magnetization and is advantageous for generating a high magnetic field.

When a soft magnetic material is used, the magnetic flux in the space at the end of the mirror magnetic field is attracted to the soft magnetic material with high magnetic permeability. The magnetic field lines (magnetic flux) of the dispersed portion are focused by the magnetic force focusing member made of each soft magnetic material.

That is, even when soft magnetic materials are used as the magnetic force focusing members 20 and 21, a large number of poles are formed at both ends of the plasma generation space 100 by these, and the number of small magnetic force focusing members 20 and 21 is the same as the number of each. A mirror magnetic field can be formed.

Therefore, as in the case of the permanent magnet, the area where one magnetic force focusing member focuses is reduced, the region where the magnetic field changes is reduced, and the distance required for focusing in the Z-axis direction is shortened. Therefore, the length of the uniform region of the magnetic field, that is, the space satisfying the ECR condition (ECR space) in the magnetic field direction becomes long, and the volume of the ECR space EE can be increased.

Further, when a soft magnetic material is used, the cost is lower than when a permanent magnet is used, and there are advantages that heat resistance and strength are high.
[Magnetic force focusing member by coil]
FIG. 5 shows a schematic configuration of the mirror magnetic field generator 3B of another example of the present invention, and FIG. 6 shows an example of the configuration of the magnetic field focusing coils 22 and 23 which are magnetic field focusing members of the mirror magnetic field generator 3B of FIG. However, each is shown.

In FIG. 5, the mirror magnetic field generator 3B is applied to an ECR ion source to generate a mirror magnetic field in which charged particles are confined in the plasma generation space 100 by a main magnetic field generating member. A cylindrical coil 16 is provided as a main magnetic field generating member, and a main magnetic field is formed inside an annular shape by passing an electric current through the coil 16.

A plurality of magnetic force focusing coils 22 and 23 for dispersing the magnetic field lines on the end side in the mirror magnetic field and focusing the dispersed magnetic field lines are arranged on the end side in the magnetic field direction in the plasma generation space 100B.

Each of the magnetic field focusing coils 22 and 23 is composed of a pair of coils that are wound concentrically around the magnetic field direction and generate a magnetic field that draws in the magnetic field lines of the mirror magnetic field by passing currents in opposite directions.

That is, as shown in FIG. 6, the plurality of magnetic force focusing coils 22 are arranged in the same plane with the two coils 221 and 222 wound concentrically close to each other. When a current is passed through the coil 221 arranged inside and the coil 222 arranged outside in opposite directions, a unidirectional annular magnetic flux (magnetic flux) BA1 as shown by an arrow is generated between them. This magnetic field BA1 draws in the magnetic field lines BA2 of the mirror magnetic field. When the direction of the current flowing through the coils 221 and 222 is changed, the direction of the drawn magnetic field line BA2 is changed.

Therefore, the arrangement direction of the magnetic force focusing coil 22 or the direction of the current may be selected according to the direction of the magnetic field.

In FIG. 5, the magnetic field focusing coil 23 is composed of a pair of coils like the magnetic field focusing coil 22, and the magnetic field for drawing the magnetic field line of the mirror magnetic field is generated by selecting the direction of the current flowing through the two coils. It is formed.

In FIG. 5, three magnetic force focusing coils 22 and 23 are arranged so as to face each other on each end side. As a result, triple annular poles are formed in the plasma generation space 100.

As described above, in the mirror magnetic field generator 3B, a plurality of annular poles are formed at both ends by the plurality of magnetic field focusing coils 22 and 23, and a large number of annular poles and a cylindrical shape formed at the center thereof. A three-layered mirror magnetic field is formed by the uniform magnetic field of. The number of magnetic force focusing coils 22 and 23 is not limited to this, and may be two or four or more.

Of the magnetic fields generated by the magnetic field focusing coils 22 and 23, the magnetic fields generated on the outer peripheral surfaces of the magnetic field focusing coils 22 and 23, that is, the magnetic fields opposite to the magnetic field generated by the coil 16, cancel each other out. Therefore, it does not become a pole at the time of mounting.

Also in the mirror magnetic field generator 3B, since the respective magnetic field focusing coils 22 and 23 focus the magnetic field lines in an annular shape, the area where one magnetic field focusing coil 22 and 23 focuses is reduced, and the region where the magnetic field changes is reduced. Therefore, the distance in the Z-axis direction required for focusing is shortened. Therefore, the length of the uniform region of the magnetic field, that is, the length of the ECR space in the magnetic field direction becomes long, and the volume of the ECR space EE can be increased.
[Explanation of Embodiment of ECR Ion Source Device]
Next, the ECR ion source device of one embodiment will be described.

FIG. 7 shows an ECR ion source device 1 according to an embodiment of the present invention. Note that FIG. 7 shows only the arrangement of the main members, and the auxiliary members and the detailed structure are not shown.

In FIG. 7, the ECR ion source device 1 includes a mirror magnetic field generator 4 for generating a mirror magnetic field that traps charged particles in the plasma chamber (plasma generation space) 110 by electron cyclotron resonance.

The ECR ion source device 1 includes a mounting flange 31, an outer yoke 32, an annular permanent magnet 33 on the upstream side, an annular permanent magnet 34 on the downstream side, auxiliary yokes 35, 36, 37 and the like.

Further, the plasma chamber 110 inside the chamber wall 38 is provided with a plurality of permanent magnets 41 and 42, an upstream cover member 43, a downstream cover member 44, a cylindrical member 45, and the like, which are magnetic force focusing members.

Further, on the upstream side of the auxiliary yoke 36, a valve device 51 for supplying gas to the plasma chamber 110 in a pulse shape is provided.

An electrode 52 for accelerating and extracting the generated ions is provided on the downstream side of the auxiliary yoke 37.

The mounting flange 31 has an outer yoke 32 inside to hold the entire ECR ion source device 1.

The permanent magnets 33 and 34 are magnetized in the radial direction, respectively, and the permanent magnet 33 on the upstream side and the permanent magnet 34 on the downstream side are magnetized in opposite directions to each other.

The auxiliary yokes 35, 36, 37 are made of a soft magnetic material, and the magnetic flux distribution by the permanent magnets 33, 34 is adjusted to form a strong magnetic field of about 2000 gauss, which is a mirror magnetic field, in the plasma chamber 110.

The auxiliary yoke 36 is provided with an introduction port 36a for introducing gas and microwaves.

The auxiliary yoke 37 is provided with an extraction port 37a for extracting (deriving) the generated ions. That is, the auxiliary yoke 37 is a disk-shaped member provided with an extraction port 37a in the central portion, and the thickness increases toward the outer circumference. An annular protrusion 37b having a substantially triangular cross section is provided around the extraction port 37a.

The chamber wall 38 is made of a non-magnetic material such as copper or an aluminum alloy, and together with the auxiliary yoke 37, electromagnetically shields the plasma chamber 110 from the outside.

On the inner end surface on the upstream side of the chamber wall 38, a plurality of permanent magnets 41 for dispersing the magnetic field lines on the end side in the mirror magnetic field formed in the plasma chamber 110 and focusing the dispersed magnetic field lines are arranged. The permanent magnet 41 is held by being pressed against the surface of the chamber wall 38 in a state of being fitted into a hole provided in the upstream cover member 43, and is held from the plasma of the plasma chamber 110 or the like. It is protected.

Further, a plurality of permanent magnets 42 are also arranged on the inner surface of the auxiliary yoke 37. The permanent magnet 42 is held by being pressed against the surface of the auxiliary yoke 37 while being fitted in the hole provided in the downstream cover member 44, and is protected from the plasma chamber 110. There is.

The tip surfaces of the plurality of permanent magnets 41 and 42 are on the same plane and form a single plane perpendicular to the Z axis. There are no other magnetic materials that affect the magnetic field between these two planes. That is, the auxiliary yokes 36, 37 and the like are outside the tip surfaces of the permanent magnets 41, 42, and it is the permanent magnets 41, 42, which are magnetic focusing members, that finally control the uniform magnetic field in the ECR space EE.

The tip surfaces of the permanent magnets 41 and 42 may be arranged so as to form one curved surface such as a paraboloid or a spherical surface instead of forming one plane.

Notches are provided in a part of the outer peripheral surfaces of the upstream cover member 43 and the downstream cover member 44, and both ends of the cylindrical member 45 fitted into the notches on the inner peripheral surface of the chamber wall 38. Is fitted.

The upstream cover member 43, the downstream cover member 44, and the cylindrical member 45 are made of a ceramic material such as alumina or ceramics. Ceramic materials have high strength, hardness, and heat resistance, can be processed into precise shapes, have extremely low electrical conductivity, and have excellent insulation properties. In addition, these may be manufactured from a glass material.

When the inner peripheral surface of the chamber wall 38, that is, the outer peripheral surface of the plasma chamber 110 is covered with a ceramic material, the volume of gas or plasma accommodated is reduced by the thickness of the ceramic material, but the volume of electron cyclotron resonance by microwaves. The volume of the original plasma chamber 110 can be made to be substantially the same as or lower than that of the original plasma chamber 110.

The valve device 51 uses a piezo element to open and close in a pulse shape at intervals of, for example, 25 Hz, that is, 40 ms to supply gas.

FIG. 8 shows the shape of the upstream cover member 43, and FIG. 9 shows the shape of the downstream cover member 44.

In FIG. 8, the upstream cover member 43 has a disk shape, and a plurality of holes 201 for fitting the permanent magnets 41 are provided on the upstream surface. The size of the hole 201 is such that the permanent magnet 41 fitted and held does not rattle inside the hole and has a tolerance.

For example, when the diameter of the permanent magnet 41 is 3 mm and the length is 3 mm, the dimensions of the hole 201 are the same, and the tolerance is set to, for example, an intermediate fit or a gap fit.

Further, the upstream cover member 43 is provided with a circular hole 202 that does not penetrate through the center of the upstream surface, and a position that partially overlaps the hole 202 at a position deviated from the center of the downstream surface. Four oval holes 203 to 206 that do not penetrate through the holes are provided at equal intervals. These holes 203 to 206 are provided at positions that do not interfere with the holes 201.

The gas supplied from the upstream side enters the plasma chamber 110 from the holes 202 via the holes 203 to 206, but does not go straight after entering the holes 202 and goes straight through the four holes 203 to 206 in the plasma chamber 110. Disperse and enter inside.

Further, the upstream cover member 43 is provided with a groove 207 at a position where it does not interfere with other holes, and an antenna as a microwave introducing means for supplying microwaves to the plasma chamber 110 is provided in the groove 207. Provided.

In FIG. 9, the downstream cover member 44 has a disk shape, and a plurality of holes 211 for fitting the permanent magnets 42 are provided on the downstream surface. A circular hole 212 penetrating is provided in the center of the downstream cover member 44, and the opening on the upstream side is chamfered to form a large-diameter opening 213. The outer peripheral surface of the protrusion 37b of the auxiliary yoke 37 is fitted into the hole 212 to hold the downstream cover member 44, and the path to the extraction port 37a is smoothly continuous.

The thickness of the upstream cover member 43 and the downstream cover member 44 is only a slight thickness added to the lengths of the permanent magnets 41 and 42, and is not unnecessarily thickened. That is, the thickness of the bottom portion of the holes 2011 and 211 provided in each is set to a thickness that takes mechanical strength and wear resistance into consideration, and is sufficiently smaller than the diameters of the permanent magnets 41 and 42, for example, 0. It is about 5 to 2 mm. By thinning the thickness of the bottom part so that the overall thickness does not become unnecessarily large, the ECR space EE by the mirror magnetic field (sub-mirror magnetic field) formed by the permanent magnets 41 and 42 is used for actual plasma generation. Available.

FIG. 10 shows an example of the magnetic flux distribution in the ECR ion source device 1, FIG. 11 shows an example of the magnetic flux distribution in the vicinity of the permanent magnet 42 arranged on the inner surface of the auxiliary yoke 37, and FIG. 12 shows the magnetic flux focusing member. Examples of magnetic flux distribution when a coil is used are shown respectively.

The magnetic flux distributions shown in FIGS. 10 and 11 are drawn by computer simulation for the structure shown in FIG. 7. The magnetic flux distribution shown in FIG. 12 is drawn by computer simulation in a state where the magnetic flux focusing coil 22 described with reference to FIG. 6 is placed in a uniform magnetic field.

As shown in FIG. 10, a substantially uniform magnetic field is formed in the plasma chamber 110.

As shown in FIG. 11, in the vicinity of the auxiliary yoke 37, magnetic field lines (magnetic flux) are dispersed by a plurality of permanent magnets 42, which are magnetic force focusing members, and the dispersed magnetic field lines are focused on the permanent magnets 42, respectively. From the figure, it can be seen that the region where the magnetic field changes toward the permanent magnet 42 is small, and the distance in the Z-axis direction required for focusing is short.

As shown in FIG. 12, the magnetic force lines (magnetic flux) are dispersed by the magnetic force focusing coil 22, which is a magnetic force focusing member, and the dispersed magnetic force lines are focused on the magnetic force focusing coil 22, respectively. From the figure, it can be seen that the region where the magnetic field changes toward the magnetic field focusing coil 22 is small, and the distance required for focusing in the Z-axis direction is short.

In the ECR ion source device 1, the valve device 51 and the introduction port 36a are examples of gas supply means, and the introduction port 36a and the antenna mounted on the upstream cover member 43 are examples of microwave introduction means. be. Further, the extraction port 37a, the electrode 52, and the like are examples of the extraction means.

As the gas, various gases such as hydrogen gas, helium gas, and argon gas are used as needed. Further, as a microwave introduction means, a waveguide or the like can be used in addition to the antenna.

Next, the operation of the ECR ion source device 1 will be briefly described.

In the ECR ion source device 1 shown in FIG. 7, the diameter of the plasma chamber 110 and the length in the Z-axis direction are set to 34 mm and the volume is set to about 30 cc due to the restriction that the volume of the plasma chamber 110 is 50 cc or less. The microwave frequency is set to 6.2 GHz so that the ECR condition is satisfied in a uniform ECR space EE of about 2000 gauss. Regarding these points, Non-Patent Document 1 mentioned above can be referred to.

Gas is supplied in a pulse shape at intervals of 40 ms to the plasma chamber 110 in which the mirror magnetic field is formed. A large amount of ions are generated in the ECR space EE for one pulsed gas. Immediately after that, the generated ions are extracted and accelerated by the voltage applied to the electrode 52, and output for the next step.

In this way, the ions are periodically pulsed from the ECR ion source device 1. During the ion output cycle, the gas remaining in the plasma chamber 110 is discharged by a vacuum suction device (not shown). Since the volume of the plasma chamber 110 is small, the remaining gas can be sufficiently discharged in a short time.

As described above, according to the ECR ion source device 1 of the present embodiment, the region of change at the end of the mirror magnetic field becomes small due to the presence of the magnetic field focusing member, and the distance in the magnetic field direction required for focusing the magnetic field lines is short. Therefore, there is an effect that the ECR space EE becomes larger accordingly.

As a result, the volume of the ECR space EE can be increased and the plasma generation efficiency can be improved.

Further, since the permanent magnets 41 and 42, which are magnetic focusing members, are held and protected by the upstream cover member 43 or the downstream cover member 44, the permanent magnets 41 and 42 can be easily held and protected. It is protected from plasma and is sufficiently prevented from deteriorating. Since the upstream cover member 43 or the downstream cover member 44 is made of a ceramic material, the ECR space EE is not reduced by this, and the ECR space EE is efficiently formed.

In the ECR ion source device 1 described above, the gas is supplied in a pulse shape by using the valve device 51, but the gas may be continuously supplied.

In the ECR ion source device 1 and the mirror magnetic field generator 4 of the above-described embodiment, the permanent magnets 33 and 34 are used to form the mirror magnetic field, but a coil may be used instead. The dimensions, shape, number, arrangement, etc. of the auxiliary yokes 35, 36, 37 and the like can be variously changed in order to form an appropriate mirror magnetic field.

The shapes, numbers, magnetic forces, arrangements, etc. of the permanent magnets 41 and 42, which are magnetic force focusing members, can be variously changed in order to make the magnetic field uniform. Instead of the permanent magnets 41 and 42, soft magnetic materials or coils may be used.

Further, a plurality of magnetic force focusing members fixed to the substrate may be used. For example, a plurality of magnetic force focusing members may be arranged and fixed on the surface of a disk-shaped substrate made of a ceramic material or the like, and this may be used as the magnetic force focusing member. Further, for example, a magnetic force focusing member made of a plurality of soft magnetic materials may be arranged and fixed on the surface of a disk-shaped substrate made of a soft magnetic material, and this may be used as the magnetic force focusing member. Further, for example, a magnetic force focusing member made of a plurality of soft magnetic materials may be integrally formed and arranged on the surface of a disk-shaped substrate made of a soft magnetic material, and this may be used as the magnetic force focusing member. The magnetic force focusing member on the upstream side and the magnetic force focusing member on the downstream side may be different from each other.

Further, an appropriate auxiliary member may be used in order to make the magnetic field in the ECR space EE uniform. For example, an annular permanent magnet is attached to the protrusion 37b of the auxiliary yoke 37 in a direction in which the magnetic field is strengthened to prevent a decrease in the magnetic field in the vicinity of the extraction port 37a and expand a uniform region of the magnetic field. May be good. Further, a hexagonal permanent magnet or the like may be arranged on the outer peripheral surface of the plasma chamber 110.

Further, different shapes and types of magnetic force focusing members may be combined. It is possible to carry out the various items described above and the items shown in the figure in appropriate combinations.

In the ECR ion source device 1 of the embodiment described above, the generated ions were extracted from the end portion in the Z-axis direction. However, instead of this, ions may be extracted from the central portion in the Z-axis direction. In this case, it is also possible to make the structure and shape of both ends of the plasma chamber 110 nearly symmetrical.

In addition, magnetic field focusing members 20, 21, permanent magnets 20a, 21a, magnetic field focusing coils 22, 23, permanent magnets 41, 42, upstream cover member 43, downstream cover member 44, or mirror magnetic field generators 3, 3B. The overall configuration, structure, shape, material, number, arrangement, magnetic field strength for ECR conditions, microwave frequency, etc. of 4 and the ECR ion source device 1 are appropriately changed according to the gist of the present invention. be able to.

1 ECR ion source device 3, 3B, 4 Mirror magnetic field generator 11, 12 Permanent magnet (main magnetic field generator)
13, 14 York 16 coil (main magnetic field generating member)
20, 21 Magnetic force focusing member 20a, 21a Permanent magnet (magnetic force focusing member)
20b, 20c, 20d Magnetic focusing member (permanent magnet body, soft magnetic material))
22, 23 Magnetic force focusing coil (magnetic force focusing member)
33,34 Permanent magnet (main magnetic field generating member)
36 Auxiliary York (York)
36a inlet (gas supply means, microwave introduction means)
37 Auxiliary York (York)
37a Extraction port (extraction means)
41,42 Permanent magnet (magnetic field focusing member)
43 Upstream cover member (cover member)
44 Downstream cover member (cover member)
51 Valve device (gas supply means)
52 Electrode (extraction means)
100,100B Plasma generation space 110 Plasma chamber (plasma generation space)

Claims (9)

A mirror magnetic field generator applied to an ECR ion source to generate a mirror magnetic field in which charged particles are confined in a plasma generation space by a main magnetic field generating member.
A plurality of magnetic force focusing members for dispersing and focusing the dispersed magnetic field lines in the mirror magnetic field are arranged on the end side in the magnetic field direction in the plasma generation space.
A mirror magnetic field generator characterized by this. The magnetic force focusing member is composed of a columnar permanent magnet having magnetic poles formed in the direction of the magnetic field.
The mirror magnetic field generator according to claim 1. The magnetic force focusing member is made of a columnar soft magnetic material.
The mirror magnetic field generator according to claim 1. The magnetic field focusing member is composed of a set of two coils that are wound concentrically around the magnetic field direction and generate a magnetic field that draws in the magnetic field lines of the mirror magnetic field by passing currents in opposite directions.
The mirror magnetic field generator according to claim 1. The magnetic force focusing members are arranged so as to be spaced apart from each other along the circumferential direction of a plurality of concentric circles.
The mirror magnetic field generator according to claim 2 or 3. The magnetic force focusing member is held by a cover member made of a ceramic material and protected from the plasma generation space.
The mirror magnetic field generator according to any one of claims 1 to 5. The magnetic force focusing member is arranged inside the plasma generation space with respect to a yoke arranged on the end side for forming the mirror magnetic field, and is arranged on the end side in the mirror magnetic field formed by the yoke. Disperse the magnetic field lines,
The mirror magnetic field generator according to any one of claims 1 to 6. The mirror magnetic field generator according to any one of claims 1 to 7.
A gas supply means for supplying gas to the plasma generation space and
A microwave introduction means for introducing microwaves into the plasma generation space, and
An extraction means for extracting the ions generated in the plasma generation space to the outside,
An ECR ion source device characterized by being equipped with. A mirror magnetic field generation method applied to an ECR ion source to generate a mirror magnetic field in which charged particles are confined in a plasma generation space by a main magnetic field generation member.
A plurality of magnetic force focusing members for dispersing the magnetic field lines on the end side in the mirror magnetic field and focusing the dispersed magnetic field lines are arranged on the end side in the magnetic field direction in the plasma generation space.
A plurality of small mirror magnetic fields are formed in the plasma generation space by the plurality of magnetic force focusing members.
A mirror magnetic field generation method characterized by this.

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