A Radio Frequency Driven DC Electron Beam Source

Abstract

A 3 cm diameter disc shaped plasma generated electron beam source, employing ion-induced secondary electron emission from cold cathodes has been demonstrated. An inductively coupled plasma generated in 2–20 mTorr argon feedstock gas provides ions which impinge on the high secondary electron emission coefficient Al2O3 cathode. A separate 13.56 MHz radio frequency bias voltage is applied to the cathode and thereby provides the effective DC field for both ion impingement and electron beam acceleration as described herein. A differentially pumped retarding potential analyzer measures the electron beam energy spectra at a location 14 cm from the cold cathode. It is found that the maximum (negative) cathode voltage sets the maximum electron beam energy, and the electron beam current is roughly set by the inductively coupled plasma power, which corresponds to the ion flux to the cathode. A crude model relating the electron beam energy spectra to the time varying cathode sheath potential provided by the rf bias shows good agreement with measured results.