The magnetic multipole line-cusp device developed by MacKenzie and associates has been adapted for use as a neutral beam ion source. It has produced high-density, large volume, quiescent, uniform hydrogen plasmas, which makes it a potential candidate for use as a plasma generator for neutral beam injectors. The device is a water-cooled cylindrical copper discharge chamber (25 cm in diameter by 36 cm long) with one end enclosed by a set of extraction grids with a 15-cm-diam multi-aperture pattern. The chamber wall serves as an anode and is surrounded by an external system of rare-earth cobalt magnets arranged in a line-cusp geometry of 12 cusps; plasma is produced by electron emission from a hot cathode assembly. This source has achieved extracted beam currents of 12 A at 18.5 kV, radial plasma density uniformities of +/-5% over a 15-cm diameter, noise levels of less than +/-0.5%, and arc efficiencies (beam current/arc power) of 0.6 A/kW.

Magnetic multipole line-cusp plasma generator for neutral beam injectors.

TITAN is a new type of ion source capable of generating high current, wide aperture beams of gas and metal ions from a broad range of elements: Mg, Al, Ti, Cr, Fe, Co, Ni, Sm, Zn, W, Pb, Ta, Re, Y, C, He, N, Ar, and Xe. A specific feature of the TITAN ion source is the use of two kinds of arc discharges, each with cold cathodes, to produce plasma for ion beam extraction. Metal ions are generated by means of the vacuum arc in the metal vapor formed in cathode spots. Gas ions, on the other hand, are provided by a low‐pressure constricted arc discharge. In a pulsed mode of operation the extraction voltage of the source ranges from 10 to 100 kV. The pulsed beam current for gas and metal ions is on the order of 1 A at pulse repetition rates up to 50 pulses per second and pulse duration of ∼400 μs. For dc operation and at an extraction voltage up to 10 kV, the ion current is as high as hundreds of milliamperes. This work outlines briefly the ion source, its design, and certain physical peculiarities observed wh...

The ‘‘TITAN’’ ion source

In an effort to develop a plasma source capable of producing a dense, quiescent, uniform plasma for extracting tens of amperes of hydrogen ions, experimental and theoretical studies on a duoPIGatron ion source have been pursued. A study of plasma generation in the duoPIGatron was begun and a discharge model was subsequently developed to explain observed source behavior. The discharge model is based on two plasmas, a cathode plasma and a PIG plasma separated by a double layer of ions and electrons, and is similar to the existing model for a duoplasmatron. This discharge model is reviewed and the importance of the double layer on plasma generation in the duoPIGatron is discussed. Source electrode modifications suggested by the model resulted in a low noise level of about ±5% and a low‐denisty nonuniformity of about ±10% over a 10‐cm diameter at a high hydrogen plasma denisty of roughly 2×1012 cm−3. This source has been operated reliably to produce a hydrogen ion beam of 15 A at 40 keV. Initial operation of ...

Plasma studies on a duoPIGatron ion source

This paper reviews the experimental study, development, and improvement of various types of processing ion sources undertaken in association with the joint program performed in recent years by the Institute of Electrophysics and the Institute of High-Current Electronics of the Russian Academy of Sciences. The beam parameters (type and energy of ions, current density, cross-sectional area of the beam, permissible content of impurities, etc.) should meet the requirements of particular ion beam treatment conditions, while the ion source itself should be simple and reliable in operation. Technical and service characteristics of the developed ion sources permit their use for ion-beam modification of materials, preparation of surfaces and ion-assisted deposition of thin films, and in some other applications. The sources under consideration employ high-current glow discharges with a hollow cathode or in crossed electric and magnetic fields, and low-pressure arc discharges and vacuum arc. Cold cathodes enhance reliability of the ion sources when they work at a high residual gas pressure or in the reactive gas media. The repetitive pulse mode of the plasma and beam generation provides optimum conditions for stable operation of the discharge, control of the average beam current over a wide range, and formation of homogeneous large-cross-section beams. The paper describes techniques used to realize high-current discharges at a reduced pressure, methods for producing a stable, dense and homogeneous plasma in a large volume, techniques of formation of large-cross-section homogeneous beams, and also findings on the mass-charge composition of the plasma and beams produced. Some design versions of the sources are given. At voltages from 10 to 100 kV, the pulse duration of 10 to 1000 μs, and the pulse repetition rate of 1 to 500 Hz these sources provide the current density of ∼1–10 mA/cm 2 in beams having the cross-sectional area of a few hundreds of square centimeters. The achieved parameters of the sources permit their use both in commercial and research applications. The use of these sources for modification of surface properties of materials has been exemplified.

High-current pulse sources of broad beams of gas and metal ions for surface treatment

The plasma production and containment system for a high‐power continuously operating magnetic multipole ion source has been designed and constructed. Preliminary tests on this system prior to high voltage extraction of large beams indicate advantageous performance for neutral‐beam injection applications. The source has produced 80 A to the extractor region at 0.33 A/cm2 with a discharge of 330 A at 80 V. Density uniformity is better than 1% over a 16‐cm diameter, dropping to −4% at 18 cm, with plasma noise of less than 3%. Gas utilizaion efficiency and atomic (H+) species output are anticipated to be high due to a source length of 40 cm. This quiet efficient performance is attributed to the use of a hollow‐tube LaB6 cathode and an improved magnetic multipole confinement system.

IBIS: A hollow‐cathode multipole boundary ion source

The 10 cm (grid diameter) duoPIGatron ion source produces pulsed hydrogen ion beams of 10–15 A beam current in the 20–40 keV energy range for a duration of a few tenths of a second. To fulfill the requirement of the next generation of high‐power neutral beam injectors for heating plasmas in CTR devices, this source has been enlarged to a version 15 cm in grid diameter. In addition, by utilizing a magnetic multipole line cusp field confinement method, the plasma created is characterized over the 15 cm grid diameter by a noise level within ±10% and spatial density variations within ±5% at a density on the order of 1012 cm−3. This larger source has operated reliably and produced a beam current exceeding 30 A of hydrogen at 27 keV. Initial operation of a 20 cm version of this source employing line cusp confinement has produced an extraction current of 60 A at 33 keV.

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W. L. Stirling

Papers

15 cm duoPIGatron ion source