High secondary electron emission for an enhanced electron density in election cyclotron resonance plasma

Abstract

The possibility of increasing the electron cyclotron resonance (ECR) plasma electron density by secondary electron emission has already been pointed out and tested by different authors. In this work the effective secondary electron emission coefficient σeff under electron impact was measured and its evolution studied as a function of the primary electron beam energy and intensity of the target bias. The usual parameters of the ECR plasma such as the electron temperature, the plasma electric potential, and the ambipolar diffusion effects in the ECR plasma chamber have been considered during these measurements. With that end in view a research facility delivering electron beams with energies in the 0–15 keV range and intensities in the 1×10−11–2×10−5 A range was developed. The study of the effective secondary electron emission coefficient σeff was carried out on different targets made of graphite, of metals such as pure and technical Al, Ta, Ni, stainless steel, and of metal-dielectric structures Al–Al2O3. For some Al–Al2O3 structures high values of σeff strongly dependent upon the primary electron beam energy and intensity and upon the target negative bias have been obtained. Such a dependence was not observed for metals. The use of highly emissive metal-dielectric structures in the plasma chamber of an ECRIS should lead to a significant enhancement of the ECR plasma electron density and consequently of the production of highly charged ions.