RU2368977C2 - Method of generating stream of negative ions - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to the technology of generating streams of negative ions and can be used in charged particle accelerators, plasma heating systems and other devices. The method of generating negative ions is based on desorption of hydrogen particles in form of negative ions from the surface of a converter, made from material with negative electron affinity, for example diamond. To increase intensity of the beam of pulled negative ions in immediate proximity of the converter, high-current gas discharge plasma is generated, which is a source of intense streams of neutral atoms and electrons, which provide for saturation of the atomic layer adsorbed on the surface of the converter and filling the conduction zone with electrons. Molecular hydrogen is fed to the converter such that, it flows through the dense gas discharge zone so as to increase degree of dissociation. Negative electrons are pulled from the converter, bypassing plasma columns. The converter used is an anode or part of an anode of a gas-discharge cell.

EFFECT: increased intensity of beam of negative ions of hydrogen isotopes without using alkali metals as catalyst.

2 cl, 1 dwg

Description

The invention relates to techniques for generating beams of negative ions and can be used in charged particle accelerators, plasma heating systems and other devices.

Known surface-plasma method for producing negative ions [1], including the supply to the discharge chamber of the source along with the main working substance additives additives substances with low ionization potential, such as cesium.

The disadvantage of this method is the flow into the discharge chamber of a substance with a low ionization potential, usually alkali metals, most often cesium. The inevitable removal of alkali metal vapors from an ion source into devices using an ion beam limits the application of this method, since it can lead to an increase in secondary electron emission or electrical breakdowns in an accelerating system and other devices.

The closest in its technical essence and the achieved result is a method of producing a beam of negative hydrogen ions without using an alkali metal, due to the desorption of hydrogen particles stimulated by electrons from the surface of a semiconductor having negative electron affinity energy, namely diamond [2]. The method includes creating a stream of atomic hydrogen directed to the surface of a converter made of diamond, subsequent bombardment of the surface by an electron beam, causing the desorption of hydrogen particles from the surface in the form of negative ions, acceleration of the formed negative ions and their formation into an ion beam. The disadvantage of this method is the low intensity of the resulting beam of negative hydrogen ions, which in this method is determined by the fact that the current of electrons entering the surface of the converter is limited by the space charge of the electron beam.

The technical result of the invention is to increase the intensity of the beam of negative ions of hydrogen isotopes without the use of alkali metals as catalysts for the formation of negative ions.

The specified technical result is achieved by the fact that in the known method for producing negative ions, including the creation of flows of atomic hydrogen and electrons directed to the surface of a converter made of a material with negative electron affinity energy, such as diamond, accelerating the formed ions and forming them into a beam, in the method, to create intense flows of atomic hydrogen and electrons in direct contact with the Converter excite the plasma of a high-current gas discharge and, wherein the molecular hydrogen is supplied to the converter so that it flowed through the dense gas discharge zone, and the negative ions are drawn from the converter, bypassing the plasma column. As the converter, an anode or part of the anode of the gas discharge cell can be used.

To obtain a technical result in the manufacture of the converter, polycrystalline diamond material obtained by gas-phase synthesis is used. The diamond materials synthesized by this method have the form of plates with sizes over 1 cm in diameter and more than 1 mm thick, which meets the requirements of using negative hydrogen ions as a converter in the source.

Known [3] is the electron affinity energy for diamond obtained by gas-phase synthesis, the surface of which is saturated with a layer of adsorbed hydrogen. The affinity energy is U _a = -1.27 eV, a negative energy value means that the minimum of the conduction band lies above the vacuum level. The binding energy of the electron with the atomic residue in the H - ion is φ = 0.75 eV. The binding energy of the hydrogen atom adsorbed on the diamond surface is about 1.6 eV [4].

When an electron transfers from the level of the conduction band to the level of electron affinity in the H - ion, an energy equal to Δ = | U _a -φ | = | -1.27-0.75 | eV = 2.02 eV, which is enough to break the bond of the atom with the surface (1.6 eV) and desorption in the form of a free negative ion.

The use of a high-current gas discharge allows to obtain an electron flux on the surface of the converter with a magnitude greater than 1 A, which significantly exceeds the electron current used in the prototype [2], which was 40 μA.

The intense dissociation of molecular hydrogen in the zone of the plasma column allows one to obtain an intense flow of atomic hydrogen on the surface of the converter, which is necessary to saturate the surface layer of adsorbed atoms and maintain it during desorption from the surface of hydrogen particles in the form of negative ions.

Mastering the gas-phase synthesis of polycrystalline diamond materials made it possible to obtain plates of such a material with a sufficiently large surface area that satisfy the requirements of using negative ions in a surface-plasma source as a converter, on which the neutrals incident on it are recharged into the negative ion stream. Such a converter is located in the region of the emission hole, which significantly increases the probability of negative ions coming out without destruction to the beam forming region and provides conditions for the generation of beams with a small energy spread and emittance.

The method can be applied to obtain negative ions of hydrogen isotopes and other elements, for example oxygen, capable of forming stable negative ions.

The drawing shows an embodiment of the method when the converter is a part of the anode of the gas discharge cell in the form of an insert made of diamond material grown by gas-phase synthesis. The gas discharge cell consists of a cathode 1 and anode 2. The anode insert 3 is made of diamond material and serves as a converter of neutral atoms into negative ions. The flow of negative ions 4 is drawn by the electrode 6. The flow of molecular hydrogen 5 is supplied to the discharge from the cathode. To implement the invention, a voltage is applied between the cathode and anode of the gas discharge cell, which causes a gas discharge with a discharge current of more than 10 A. From the cathode side, a working gas, molecular hydrogen, which substantially dissociates in the discharge plasma and flows to the anode in in the form of a stream of atomic particles. The anode also receives a current of electrons of a gas discharge, the magnitude of which is more than 10 A, which is much larger than the electron current supplied to the converter in the prototype. Electrons from a gas discharge plasma flow through an anode insert of diamond material, creating a concentration of carriers in the conduction band of diamond. Hydrogen atoms adsorbed on a diamond surface capture electrons from the conduction band to the electron affinity level with the release of energy sufficient for desorption and escape from the surface in the form of negative ions, and are formed into a beam 4 by pulling electrodes 6.

The proposed method for producing a beam of negative hydrogen ions due to the excitation of a plasma of a high-current gas discharge has a high intensity of the resulting negative ion beam and can be used on a high-current linear accelerator.

Literature

1. V.G. Dudnikov. The method of obtaining negative ions, Copyright certificate Cl. H01J 3/04, No. 411542, Application 03.03.1972, Bulletin No. 2, 1974.

2. C. Goden and G. Dollinger. Electron stimulated desorption on diamond (100) as a negative hydrogen source, Applied Surface Science, Volume 147, Issues 1-4, May 1999, Pages 107-113.

3. J.B. Cui, J. Ristein, L. Lay, Phys. Rev. Letters, 81, p. 429-432 (1998).

4. M. McConial, M. L. Kempel, M. S. Hammond, K. D. Jamison, Jorn. Vac. Sci. Technol. A 14 (4) (1996) p. 2308.

Claims (2)

1. A method of producing negative ions, including the creation of flows of atomic hydrogen and electrons directed to the surface of a converter made of a material with negative electron affinity energy, such as diamond, accelerating the ions formed and forming them into a beam, characterized in that for creating intense atomic flows hydrogen and electrons directed to the surface of the converter, in direct contact with the converter, excite a plasma of a high-current gas discharge, while the molecular The rod is fed to the converter in such a way that it flows through the dense gas discharge zone, and negative ions are pulled from the converter, bypassing the plasma column. 2. The method according to claim 1, characterized in that the anode or part of the anode of the discharge cell is used as a converter.