Proton Production in the Low Voltage Arc

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Abstract
Further investigations with the proton source previously described have yielded considerable information about the processes involved in its operation. The tube has been redesigned with the object of obtaining large proton currents in a beam. Ions are drawn out of the arc through a hemispherical grid inserted in the cylindrical electrode. Part of the resulting converging beam passes through a hole in a second electrode which separates the arc chamber from a region maintained at a lower pressure by differential pumping. Total currents of over 0.5 milliampere at current densities of about 8.0 milliamperes per square cm were obtained on the low pressure side. The ratio of proton current to total current was as high as 98 percent with pressures in the discharge tube of 0.3 to 0.4 mm. In order to attain this percentage it was necessary to maintain certain minimum potentials on the cylinder and second electrode. At the same time the metal parts must be prevented from exceeding red heat since an adsorbed layer of hydrogen on the walls is necessary to prevent recombination of atomic hydrogen there. The proton currents obtainable are limited by the speed of the differential pumping and the degree of vacuum desired. The observed pressure ratios were improved by a factor of two when the arc was in operation owing to the increased temperature of the gas streaming through the hole.

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