Low Voltage Proton Sources

Abstract

Further experiments have been carried out with a view towards increasing the proton percentage obtainable from capillary arc sources previously described. The collision method of breaking up molecular ions has been investigated. Although no difficulty was experienced in refocusing the scattered ions, no evidence was found for break-up in the absence of magnetic fields. Rather than investigate these possibilities further, a quartz capillary was tried, using a simple beveled outlet. This eliminated the rapid disintegration of the quartz by secondary electrons from any probe electrode, but there was still evidence of gradual disintegration of the quartz by low speed electrons in the discharge. The absence of excessive heating indicated that the capillary might as easily be made of Pyrex. A Pyrex capillary source was therefore tried. In a 3.5 mm capillary, heating was not excessive at arc currents below 0.3 ampere. The proton percentages ranged up to 20 percent. Following the experience of Wood, water vapor was introduced, and resulted in a marked increase in the proton percentage (a factor of about 4). This source possesses the advantages of slightly greater ion current efficiency, requires no cooling, is easily constructed, and is free from impurities.