Investigations of the Transient Behavior of the Cathode Fall Region in Planar and Hollow Cathodes
Final rept. 1 Jul 1989-1 Jul 1992
POLYTECHNIC UNIV FARMINGDALE NY WEBER RESEARCH INST
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Recently there has risen a strong interest in producing negatively charged ion beams such as H-, for space based accelerators. The negative ions are generated in the plasma of an arc or glow discharge. The electrons are separated from the negative ions by a magnetic field. In such an environment various plasma and discharge instabilities can occur resulting in undesirable Megahertz noise of broad spectrum in the beam. It has been experimentally shown that the noise could be reduced by using a large ballast resistor in the discharge circuit. However to effectively suppress the noise, the value of the resistance would be prohibitively high. This report describes the design of a possible noise suppression circuit utilizing power transistors in a pulsed discharge. Using power transistors it is possible to obtain high dynamic impedance but still with sufficiently low D.C. resistance to stabilize the instabilities. The noise is present within a Negative Ion Source obtained from Los Alamos National Laboratory AT division. This report describes the design of a Gate Turnoff Thyristor GTO pulsing circuit for the Negative Ion Source which includes the modification of an existing gate drive unit for a low power GTO. The Negative Ion Source had been pulsed by a capacitive bank discharge circuit. This GTO pulsing circuit has been successfully tested on a Hollow Cathode discharge.
- Electrical and Electronic Equipment
- Particle Accelerators
- Plasma Physics and Magnetohydrodynamics