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A high-frequency discharge ion source Chow, Richard Hing

Abstract

A high-frequency discharge ion source was developed yielding 45% protons in an 800 microampere, 14 kv energy focused beam of positive hydrogen ions. Higher ion currents could be delivered at higher voltages. The discharge was excited in a pyrex discharge tube, 1¼ inches in diameter and 9 inches long, by a 210 Mc/sec. push-pull, oscillator capable of delivering 120 watts power. An electrostatic potential difference of 1.8 kv applied axially with the discharge tube, accelerated the positive ions formed in the discharge toward the exit canal. A magnetic field of 240 gauss, also applied axially, shaped the discharge conically, and intensified the redness of the discharge, causing the Balmer lines to appear prominently when the discharge was viewed through a spectroscope. The ions emerging from the exit canal were focused by an electrostatic lens using a potential difference of 12 kv. The hydrogen pressure in the discharge tube measured 17 microns, and the rate of hydrogen consumption measured 11 cc. per hr. The proton percentage was found to depend on the oscillator power and critically on the gas pressure. The magnetic field increased the proton percentage, but in an unpredictable manner. It was also found that the focusing lens in front of the probe canal exerted an extracting action on the ions in the discharge; influencing very strongly the total ion beam current collected. The general performance of the ion source was found to be satisfactory.

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