Plasma studies on a duoPIGatron ion source

Abstract

In an effort to develop a plasma source capable of producing a dense, quiescent, uniform plasma for extracting tens of amperes of hydrogen ions, experimental and theoretical studies on a duoPIGatron ion source have been pursued. A study of plasma generation in the duoPIGatron was begun and a discharge model was subsequently developed to explain observed source behavior. The discharge model is based on two plasmas, a cathode plasma and a PIG plasma separated by a double layer of ions and electrons, and is similar to the existing model for a duoplasmatron. This discharge model is reviewed and the importance of the double layer on plasma generation in the duoPIGatron is discussed. Source electrode modifications suggested by the model resulted in a low noise level of about ±5% and a low-denisty nonuniformity of about ±10% over a 10-cm diameter at a high hydrogen plasma denisty of roughly 2×1012 cm−3. This source has been operated reliably to produce a hydrogen ion beam of 15 A at 40 keV. Initial operation of a 20-cm source employing magnetic multipole line cusp confinement [W. L.,Stirling, C. C.,Tsai, P. M.,Ryan, Rev. Sci. Instrum. 48, 533 (1977)] has delivered a beam of 60 A at 33 keV.