JPS631699B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas discharge apparatus, and in particular to an electron ion source that can be effectively used in electron beam welding and processing of fabricated pieces.

A Penning cell is known as a conventional gas radiation ion source. It consists of an annular anode, a device that creates a defined magnetic field near the anode in the direction of the symmetry axis of the hole in the anode, two flat cathodes that are electrically coupled to each other and placed on opposite sides of the anode, and one part of this cathode. One consists of an emitter cathode with a radiation channel. A withdrawal mechanism is located on the opposite side of the radial channel from the outer aperture. The first cathode hole, the anode hole, the radiation channel and the extraction mechanism are all arranged coaxially. (For example, M.D.Gabovitch
“Plasma Ion Sources.Physics and
Techniques; Moscow, “Atomizdat”, 1972,
P.116).

In the above-mentioned ion source, the magnitude of the current extracted by the extraction mechanism is small, and a stable glow discharge that does not form a cathode spot in the Penning cell results in a low density of charged particles per unit.

Also, in electron ion sources different from Penning cells, the first cathode is a hollow cylinder with an axis of symmetry of the cavity along the axis of the hole in the anode, the axis of the emission channel of the emitter cathode, and the axis of the extraction mechanism (e.g. , USSR Inventor′s Certificate No.456322;
cl.H 01J3/02, 1973).

Like the ion source described above, this ion source extracts particles longitudinally from a reflective discharge hollow cathode. This results in a relatively high rate of electron extraction due to the use of a hollow cathode with a cavity that facilitates discharge in the axial direction of the radiation channel.

However, the aforementioned ion sources have deep modulation of the extraction current (approximately 80-100%). In a discharge chamber equipped with the annular anode and cathode described above, conditions exist that tend to produce rotational azimuth non-uniformity in the discharge.
Even if the extraction voltage by the extraction mechanism is constant, the extraction current is modulated at a repetition frequency of 100 to 200 KHz (pulse current). The use of known ion sources is undoubtedly generally difficult to implement.

The invention consists in providing an electron ion source in which the discharge chamber has a sufficiently high sampling effect and prevents modulation of the charged particle flux.

The above object is achieved by an electron ion source having the following configuration.

an annular anode, a device for creating a prescribed magnetic field near the anode in the direction of the symmetry axis of the hole in the anode, a hollow cylindrical cathode with the axis of the cavity parallel to the vector direction of the magnetic field, arranged coaxially with the cavity of the hollow cylindrical cathode. The hollow cylindrical cathode and the cathode with a radiation channel are electrically coupled to each other and placed on opposite sides of the anode, and an extraction mechanism is disposed on the opposite side of the exit hole of the radiation channel. The axis of symmetry of the anode hole is offset from the axis of the cylindrical cathode cavity by a distance not exceeding the sum of the radius of the anode hole and the radius of the cylindrical cathode cavity, resulting in rotational azimuthal plasma inhomogeneity. electron ion source that inhibits the generation of ion and modulates the output current.

The electron ion source according to the invention prevents modulation of the extraction current and establishes a high extraction efficiency. Furthermore, the structure is simple and operation is reliable.

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

The electron ion source according to the invention consists of an annular anode 1 (FIGS. 1 and 2) and an anode which serves as a device for creating a defined magnetic field B (shown in dotted lines) in the vicinity of the anode 1 in the direction of the axis of symmetry 3 of the bore of said anode 1. 1 and a coaxial permanent magnet 2. A hollow cylindrical cathode 4 and an emitter cathode 5 are electrically coupled to each other and placed on opposite sides of the anode 1. The cavity 6 of the cathode 4 and the radiation channel 7 of the cathode 5 are exposed to the magnetic field B
is placed coaxially with the vertical axis parallel to the vector direction. Coaxially located opposite the exit hole of the radiation channel 7 is an extraction mechanism (extraction electrode 8 in the embodiment of the invention). The holes in the annular anode 1 are placed at a distance "a" in which the axis of symmetry 3 in the holes does not exceed the sum of the radii of the holes 6 in the cathode 4 with respect to the axis of symmetry of the cavity 6 in the cathode 4. It will be destroyed. Advantageously, this distance "a" is equal to the radius of the cavity 6. The anode 1, the magnet 2, the cathodes 4 and 5, and the extraction electrode 8 are made of a flange 1 made of an insulating material and a conductive material.
It is placed in an enclosure 9 made of seals with 0,11. A space defined by the anode 1 , the hollow cylindrical cathode 4 and the emitter cathode 5 forms a discharge chamber 12 . A current source 13 located outside the enclosure 9 applies a voltage to the electrodes (anode 1 and cathode 5) of the discharge chamber 12. Also, a power source 14 located outside the enclosure 9 creates an extraction voltage between the cathode 5 and the extraction electrode 8. The output terminals of the power supplies 13, 14 are respectively connected to the electrodes of the electron ion source through sealed input terminals 15 in the wall of the insulating enclosure 9.

In FIG. 1, the connection polarity of the power source 14 is such that electrons are extracted from the discharge. In order to obtain an ion beam, it is necessary to convert the connection polarity of the power source 14.

Next, the operation will be explained.

A working gas is introduced into the discharge chamber 12 through the cathode cavity 6.
It is supplied until the pressure reaches ×10 ^-2 torr.

A Penning discharge occurs in the discharge chamber 12 at an applied voltage between the cathodes 4, 5 and the anode 1 and at a specified pressure. When the discharge current increases and the cathode voltage drop region becomes smaller than the opening of the cavity 6 of the cathode 4, the Penning discharge plasma penetrates into the cavity 6, creating a hollow cathode effect. The Penning discharge transforms into a hollow cathode reflection discharge characterized by a high plasma concentration along the cavity axis. Since the axis of the cavity 6 of the cathode 4 is offset with respect to the axis of the anode 1, the area where the discharge plasma is most concentrated and always offset with respect to the opening of the cavity is also spaced apart with respect to the axis of the anode 1. It's on. In such a state, the formation of rotational azimuth nonuniformity is prevented,
This becomes a factor that hinders modulation of the output current of the ion source. This can be explained as a non-uniformity of the electric field within the discharge chamber 12.

The optimum situation occurs when the arrangement of the shafts is equal to the opening radius of the cavity 6. In addition to preventing modulation of the ion source output current, the scent electron extraction effect is essentially preserved.

As described above, the anode 1 with holes spaced apart in the axial direction
The use of 20.degree. C. prevents modulation of the extraction current and effectively extends the range of use of the ion source according to the present invention.

[Brief explanation of the drawing]

FIG. 1 is a simplified cross-sectional view of an electron ion source according to the invention, and FIG. 2 is a plan view of an annular anode according to the invention. In the figure, 1...anode, 3...axis of hole in anode, 4
... hollow cylindrical cathode, 5 ... emitter cathode, 6 ... cathode cavity, 7 ... radiation channel, 8 ... extraction electrode.

Claims (1)

[Claims] 1. An annular anode 1, a device for creating a prescribed magnetic field B near the anode in the direction of the symmetry axis 3 of the hole in the anode, and a cavity 6 having an axis parallel to the vector direction of the magnetic field B. A hollow cylindrical cathode 4, a cathode 5 disposed coaxially with the cavity 6 of the cylindrical cathode 4 and having a radiation channel 7, the hollow cylindrical cathode 4 and the cathode 5 having the radiation channel 7 are electrically coupled to each other and serve as an anode to each other. 1 and comprises an extraction mechanism 8 on the side opposite the exit hole of the radiation channel 7, which aligns with the axis of symmetry 3 of the hole of the anode 1.
is offset from the axis of the cavity 6 of the cylindrical cathode 4 by a distance "a" which does not exceed the sum of the radius of the hole in the anode 1 and the radius of the cavity 6 in the cylindrical cathode 4, and An electronic ion source characterized by inhibiting generation and modulation of output current. 2. Electron ion source according to claim 1, characterized in that the value "a" of the deflection distance is equal to the radius of the cavity 6 of the cylindrical cathode 4.