ABSTRACT
An ion source based on a hollow-cathode Penning discharge was switched to a high-current pulsed mode (tens of amperes and tens of microseconds) to produce an intense hydrogen ion beam. With molecular hydrogen (H2), the ion beam contained three species: H(+), H2(+), and H3(+). For all experimental conditions, the fraction of H2 (+) ions in the beam was about 10 ÷ 15% of the total ion beam current and varied little with ion source parameters. At the same time, the ratio of H(+) and H3(+) depended strongly on the discharge current, particularly on its distribution in the gap between the hollow and planar cathodes. Increasing the discharge current increased the H(+) fraction in ion beam. The maximum fraction of H(+) reached 80% of the total ion beam current. Forced redistribution of the discharge current in the cathode gap for increasing the hollow cathode current could greatly increase the H3(+) fraction in the beam. At optimum parameters, the fraction of H3(+) ions reached 60% of the total ion beam current.
ABSTRACT
A bulk plasma source, based on a high-current dc glow discharge with electron injection, is described. Electron injection and some special design features of the plasma arc emitter provide a plasma source with very long periods between maintenance down-times and a long overall lifetime. The source uses a sectioned sputter-electrode array with six individual sputter targets, each of which can be independently biased. This discharge assembly configuration provides multifunctional operation, including plasma generation from different gases (argon, nitrogen, oxygen, acetylene) and deposition of composite metal nitride and oxide coatings.
ABSTRACT
An ion source based on a two-stage discharge with electron injection from a cold emitter is presented. The first stage is the emitter itself, and the second stage provides acceleration of injected electrons for gas ionization and formation of ion flow (<20 eV, 5 A dc). The ion accelerating system is gridless; acceleration is accomplished by an electric field in the discharge plasma within an axially symmetric, diverging, magnetic field. The hollow cathode electron emitter utilizes an arc discharge with cathode spots hidden inside the cathode cavity. Selection of the appropriate emitter material provides a very low erosion rate and long lifetime.
ABSTRACT
We have made and tested a very low energy gaseous ion source in which the plasma is established by a gaseous discharge with electron injection in an axially diverging magnetic field. A constricted arc with hidden cathode spot is used as the electron emitter (first stage of the discharge). The electron flux so formed is filtered by a judiciously shaped electrode to remove macroparticles (cathode debris from the cathode spot) from the cathode material as well as atoms and ions. The anode of the emitter discharge is a mesh, which also serves as cathode of the second stage of the discharge, providing a high electron current that is injected into the magnetic field region where the operating gas is efficiently ionized. In this discharge configuration, an electric field is formed in the ion generation region, accelerating gas ions to energy of several eV in a direction away from the source, without the use of a gridded acceleration system. Our measurements indicate that an argon ion beam is formed with an energy of several eV and current up to 2.5 A. The discharge voltage is kept at less than 20 V, to keep below ion sputtering threshold for cathode material, a feature which along with filtering of the injected electron flow, results in extremely low contamination of the generated ion flow.
ABSTRACT
The paper presents the results of tests of a new compact two-stage bulk gas plasma gun. The plasma gun is based on a nonself-sustained gas discharge with an electron emitter based on a discharge with a self-heating hollow cathode. The operating characteristics of the plasma gun are investigated. The discharge system makes it possible to produce uniform and stable gas plasma in the dc mode with a plasma density up to 3x10(9) cm(-3) at an operating gas pressure in the vacuum chamber of less than 2x10(-2) Pa. The device features high power efficiency, design simplicity, and compactness.
ABSTRACT
We present the results of experiments leading to improvement in bulk plasma uniformity of a constricted-arc discharge system with electron injection. The steady-state discharge was in argon, at a gas pressure of 0.5 mTorr, and operated with a main discharge voltage between 20 and 100 V and current between 3 and 15 A. The radial plasma distribution was measured with a movable Langmuir probe. We find that geometric modification of the intermediate electrode exit aperture and the main discharge cathode add little to the plasma uniformity. Improved bulk plasma uniformity is observed when a special distributing grid electrode is used and the main discharge voltage is less than 20-30 V. The application of a weakly divergent magnetic field in the region of the intermediate electrode exit aperture decreases the plasma nonuniformity from 20% to 14% over a radial distance of 30 cm. The plasma uniformity was further improved by compensating the magnetic self-field of the injected electron beam by a reverse magnetic field produced with a special electrode compensator. It is shown that an increase in discharge current causes a proportional increase in back current in the distributing electrode. The approach allows a decrease in plasma nonuniformity from 20% to 13% over a radial distance of 30 cm.
ABSTRACT
A novel approach to low-energy, high-current, gaseous ion beam generation was explored and an ion source based on this technique has been developed. The source utilizes a dc high-current (up to 20 A) gaseous discharge with electron injection into the region of ion generation. Compared to the conventional end-Hall ion source, the locations of the discharge anode and cathode are inverted: the cathode is placed inside the source and the anode outside, and correspondingly, the discharge current is in the opposite direction. The discharge operates in a diverging axial magnetic field, similar to the end-Hall source. Electron generation and injection is accomplished by using an additional arc discharge with a "cold" (filamentless) hollow cathode. Low plasma contamination is achieved by using a low discharge voltage (avoidance of sputtering), as well as by a special geometric configuration of the emitter discharge electrodes, thereby filtering (removing) the erosion products stemming from the emitter cathode. The device produces a dc ion flow with energy below 20 eV and current up to 2.5 A onto a collector of 500 cm(2) at 25 cm from the source edge, at a pressure > or =0.02 Pa and gas flow rate > or =14 SCCM. The ion energy spread is 2 to 3 eV (rms). The source is characterized by high reliability, low maintenance, and long lifetime. The beam contains less than 0.1% of metallic ions. The specific electric energy consumption is 400 eV per ion registered at the collector. The source operates with noble gases, nitrogen, oxygen, and hydrocarbons. Utilizing biasing, it can be used for plasma sputtering, etching, and other ion technologies.
ABSTRACT
The results of an experimental study of low-energy (<200 eV) ion flux generation with space charge neutralization are presented. Argon was used as a working gas. The working gas pressure in the vacuum chamber was 2-4 x 10(-2) Pa. Ion beam was extracted from the hollow cathode of main discharge plasma by a single mesh extractor with subsequent deceleration of ions to a required energy in a layer between the mesh and the beam plasma. The ion beam current was measured on the collector located on the distance of 30-60 cm from the discharge system. The penetration of electron component from the main discharge plasma through the mesh into the region of the ion beam drift space was realized by potential barrier reduction, in conditions of the optimal extractor potential with respect to the hollow cathode. The space charge neutralization of low-energy ion beam resulted in drift space plasma potential reduction and ion beam current growth. At the main discharge current of 1 A and main discharge voltage of 300 V, the ion beam current of up to 100 mA with the ion energy of 50-150 eV was obtained.