RU2233505C2 - Gas-discharge ion source - Google Patents

Abstract

FIELD: electrical engineering, applicable in accelerating equipment, in particular, in accelerating gas-filled tubes of neutron generators.

SUBSTANCE: the gas-discharge ion source has an anode and a non-heater cathode that is made in the form of a cylindrical winding of conducting material with a layer with a high secondary ion-electron emission ratio located on its surface, the cathode end is positioned in the gas-discharge chamber of the ion source and may be made of an aluminum band or foil.

EFFECT: enhanced efficiency of ion sources.

2 cl, 2 dwg

Description

The invention relates to devices for producing ion beams and can find application in accelerator technology, gas-filled accelerator tubes of neutron generators.

A known ion source (see, for example, Physics and technology of ion sources. Edited by J. Brown. M .: Mir, 1998, p. 181), in which the generation of ions is carried out in the Penning discharge with a hot cathode.

However, such sources have a complex structure and low reliability due to the presence of a heated element in the structure.

For the prototype, an ion source was selected (see, for example, US patent No. 4282440, class H 01 J 47/06 1981, Neutron accelerator tube having improved ionization section) with a Penning discharge with a cold cathode.

The source works as follows. The gas discharge chamber of the ion source is formed by a cylindrical anode and a cold cathode, consisting of two disks located coaxially with the anode. Disks are placed at the ends of the cylindrical anode. One of the disks has a hole for extracting ions. In a cylindrical volume bounded by the anode and disks, a magnetic field is created parallel to the axis of the system. The anode and cathode are placed in the volume of the vacuum chamber into which the working gas is supplied. A voltage is applied between the anode and cathode, as a result of which the electrons in the gas discharge chamber are accelerated and ionize the gas molecules. The formed ions move to the cathode. Part of the ions leaves the source through an opening in the cathode, and part of it bombards the cathode, knocking electrons out of it. In addition, in the presence of microinhomogeneities on the cathode surface, electrons are emitted from them as a result of field emission. The efficiency of ionization of the working gas depends on the magnitude of the coefficient of secondary ion-electron emission and the magnitude of field emission on the surface of the cathode. The coefficient of ion-electron emission largely depends on the presence of microinclusions of metal oxides on the surface of the cathode (see, for example, Gabovich MD, Physics and Technique of Plasma Ion Sources. M: Atomizdat, 1972).

On the surface of fresh cathodes, as a rule, there are oxide films. However, these films are quickly atomized by ion bombardment of the cathode. Microinhomogeneities, which are a source of field emission, are also rapidly dispersed.

For this reason, the efficiency of the source rapidly decreases and stabilizes at a level corresponding to a clean, smooth cathode surface.

The invention is aimed at increasing the efficiency of the ion source by creating such a cathode, on the working surface of which there would always be microinclusions, for example, metal oxides, providing a high coefficient of ion-electron emission, and microinhomogeneities, providing increased field emission from the cathode.

For this, in a gas discharge ion source, including the anode and unheated cathode, the cathode is made in the form of a dense cylindrical winding of conductive material, on the surface of which there is a layer with a high secondary ion-electron emission coefficient, with the end of the cathode perpendicular to the winding axis located in the gas discharge chamber ion source, the conductive material may be an aluminum foil tape with an oxide film on the surface, or a compound of thin aluminum, oxidized from the surface of the plaz in, or set of wires with a thin aluminum oxide film on the surface, the ends of which form the ends of the cathode.

Figure 1 shows a diagram of the proposed gas discharge ion source; figure 2. presents a view of the working surface of the cathode from the gas discharge chamber.

The gas-discharge ion source (see Fig. 1) consists of a cylindrical vacuum chamber 1 of non-magnetic material. A cylindrical anode 2 and an unheated cathode 3, consisting of two electrically connected parts placed coaxially with the anode at its ends, are placed in the chamber 1. In one part of the cathode there is a hole 4 for extracting ions.

Each part of the cathode is made of thin oxidized aluminum foil from the surface by tight cylindrical winding, or from a combination of thin aluminum plates, or from a set of thin aluminum wires, the ends of which form the ends of the parts of the cathode. A cylindrical vacuum chamber 1 is placed in the cavity of a cylindrical magnet 5, which creates a magnetic field in the gas discharge chamber of the ion source.

In this design, oxides are always present on the working surface of the cathode, providing increased electron emission. In this case, the spraying of oxides to pure aluminum, as in the prototype, is impossible. In addition, as a result of the difference in the sputtering rates of pure aluminum and oxide, a strong microinhomogeneity appears on the working surface, which increases field emission. As a result of the presence of traces of oxides and microinhomogeneities on the working surface of the cathode during long-term operation, the efficiency of ionization of the working gas will be increased in comparison with the prototype.

Claims (2)

1. A gas-discharge ion source, including a gas-discharge chamber, anode and an unheated cathode, characterized in that the cathode is made of a conductive tape or foil having a layer with a high secondary ion-electron emission layer on the surface by tight cylindrical winding, the cathode end being located in gas discharge chamber of an ion source. 2. The gas-discharge ion source according to claim 1, characterized in that the conductive tape or foil is made of aluminum.

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