JPH0766765B2 - Duopigatron type ion source - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a duopigatron type ion source.

[0002]

2. Description of the Related Art A duopigatron type ion source comprises a cathode (hot filament) arranged in an ion generating chamber,
An anode arranged to face the cathode, an intermediate electrode arranged between the two, a reflection electrode arranged on the downstream side of the anode, and a central axis of an orifice formed in each electrode. It has a magnet for forming a magnetic field in a certain direction, and has a structure combining a duoplasmatron structure with a PIG structure that causes electrons generated from a hot filament to reciprocate several times between an intermediate electrode and a reflective electrode. . Then, plasma is generated between the cathode and the reflection electrode, and an electric field is applied to the plasma to emit an ion beam to the downstream side of the reflection electrode.

The duopigatron type ion source having the above structure is suitable as an ion source for producing multiply charged ions because it can obtain high density plasma.

[0004]

By the way, according to the conventional duopigatron type ion source, it is possible to generate high density plasma, but it is difficult to extract the beam as it is even if an electric field is applied to the high density plasma. . That is, when the plasma has a high density, the shape of the sheath surface of the plasma that oozes out from the orifice of the reflective electrode becomes a convex shape on the extraction side, and in such a state,
Since the beam easily diverges even when an electric field is applied, it is not possible to efficiently extract a large current ion beam.

Therefore, conventionally, a plasma expansion cup or the like is provided on the downstream side of the reflection electrode to widen the diffusion cross-sectional area of the plasma and reduce the density of the plasma, so that the shape of the sheath surface of the plasma is opposite to the drawing direction. The method of making it convex is adopted. However, in this method, although it is possible to obtain a high-current ion beam, the expanded cross-sectional area of the plasma becomes wider in the expansion cup, so that the emittance, which is one of the quantities that determines the quality of the ion beam, increases. There was a problem of being lost.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide an ion source capable of emitting a multiply charged ion beam with a large current and a small emittance. .

[0007]

In order to achieve the above-mentioned object, in the present invention, FIG.
As shown in, the length of the orifice 4a of the reflective electrode 4 in the axial direction Z is extended toward the anode 2 by a cylindrical wall body 4b protruding from the peripheral portion toward the anode 2 side.

[0008]

By extending the length of the orifice 4a of the reflective electrode 4 in the axis Z direction toward the anode 2 side, it becomes possible to directly extract a high-current beam from the high-density plasma. This is because, of the high-density plasma pinched by the magnetic field, only the plasma with uniform directionality near the central axis Z exudes from the orifice 4a to the downstream side (high vacuum side),
It is inferred that the sheath surface of the exuded plasma has a convex shape in the direction opposite to the beam extraction direction.

[0009]

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention. An anode 2 is arranged so as to face a cathode 1 composed of a hot filament 1a that generates electrons. Also, cathode 1
The intermediate electrode 3 is disposed at a predetermined position between the anode 2 and the anode 2. Further, a reflective electrode 4 is arranged on the downstream side of the anode 2 so as to face the anode 2. The intermediate electrode 3 is electrically placed at an intermediate position between the cathode 1 and the anode 2 by the power supplies 7 and 8 and the resistors R3 and R2.

Anode 2, intermediate electrode 3 and reflective electrode 4
Are orifices 2a and 3a centered on the axis Z, respectively.
And 4a are formed. However, the orifice 4a of the reflective electrode 4 has a shape in which the length in the axis Z direction is elongated toward the reflective electrode 2 side by the cylindrical wall 4b protruding from the peripheral edge toward the anode 2 side. . On the other hand, a magnet 5 for forming a magnetic field is arranged along the axis Z in the outer peripheral portion of the electron gun constituted by the filament 1a and the intermediate electrode 3. Further, the extraction electrode 6 is arranged so as to face the reflection electrode 4. A predetermined gas atmosphere is maintained on the upstream side of the reflective electrode 2, and a high vacuum is maintained on the downstream side thereof.

Next, the operation of the embodiment of the present invention will be described. First, the electric current formed from the intermediate electrode 3 and the magnetic field generated by the magnet 5 narrow the electron flow from the hot filament 1a.
After the electrons pass through the intermediate electrode 3, the axis Z by the magnet 5
While being swirled by the action of the magnetic field in the direction and the electric field of the anode 2, the intermediate electrode 3 and the reflective electrode 4 reciprocate several times. Due to the above action, the high density plasma P is generated between the cathode 1 and the reflective electrode 4, and at the same time, the plasma P is pinched by the magnetic field. Then, the pinched plasma P exudes to the high vacuum side through the orifice 4a of the reflection electrode 4, and the extraction electrode 6 extracts the ions in the plasma to obtain an ion beam.

As described above, the orifice 4 of the reflective electrode 4
By making a have a shape as shown in FIG. 1, even if the plasma passing through the orifice 4a has a high density, it is possible to directly emit a large-current ion beam without reducing the density. It has become possible. This is because, of the high-density plasma P pinched by the magnetic field, only the plasma with good directivity in the vicinity of the central axis Z is guided into the orifice 4a, and the length of the orifice 4a in the axial Z direction is long. It is presumed that the sheath surface of the plasma that oozes out to the vacuum side has a convex shape in the direction opposite to the beam extraction direction.

[0013]

As described above, according to the present invention, the axial length of the orifice of the reflective electrode forming the PIG type is generated by the cylindrical wall protruding from the peripheral portion of the orifice. Since it is extended toward the side, it is possible to directly extract the ion beam from the high-density plasma generated by the combination of the PIG type and the duoplasmatron, which results in high brightness, that is, a small emittance and a large current ion beam. As a result, it is possible to realize an ion source with a high production ratio of multiply charged ions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

[Explanation of symbols]

 1 ... Cathode 2 ... Anode 3 ... Intermediate electrode 4 ... Reflective electrode 4a ... Orifice 4b ... Cylindrical wall 5 ... Magnet 6 ... ... Lead electrodes

Claims (1)

[Claims] 1. A cathode disposed in the ion generating chamber,
An anode, which is arranged so as to face the cathode and has an orifice formed along the direction of ejecting ions, and an intermediate portion, which is arranged between the anode and the cathode and has an orifice coaxial with the anode. An electrode, a magnet that forms a magnetic field in a direction along the axis of the orifice, and is disposed on the opposite side of the intermediate electrode facing the anode,
Further, in an ion source provided with a reflecting electrode in which an orifice coaxial with the anode is formed, the orifice of the reflecting electrode has an axial length which is defined by a cylindrical wall protruding from the peripheral portion toward the anode. Is extended toward the anode side, and is a duopigatron type ion source.