Production and Analysis of a Large-Diameter Plasma Beam

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Abstract
A continuously operating low‐velocity plasma accelerator is described which has a beam diameter of 3.6 cm. The beam is produced by extracting ions from a discreetly generated singly charged ion plasma in the following manner: A fine wire mesh placed so that one side is exposed to the plasma acts as a solid flat cathode when given a negative potential. Some of the ions which are attracted to the mesh pass between the wires and stream into the region behind the mesh where they enter a field of thermionically emitted electrons. The resulting beam consists of a stream of parallel‐flowing ions with a compensated negative space‐charge atmosphere of randomly moving electrons. Beam densities of 2×108 ions/cm3 of 100‐ev Hg+ ions are obtainable 15 cm from the extractor. Gas pressures are maintained which provide mean free paths which are long compared to the tube dimensions. The diagnostic techniques used to analyze the beam parameters are described. The system is versatile and may be altered to permit the use of other gases, pressures and ion velocities.

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