Studies on Extraction of Zirconium Plasma that is produced by Electron-Impact Ionization

摘要

When a high-intensity (～250 mA/cm~2), high-energy (～48 kV) electron-beam (～85 kW) produces zirconium vapor in an evacuated vessel, zirconium plasma is formed in the free space above the evaporating source. The plasma is produced by electron-impact ionization of the evaporated atoms and expands with the vapor. It is weakly ionized (～0.1% degree of ionization) and has low electron temperature (～0.3 eV). In applications like laser based isotope separation and purification of alloys, this electron-beam generated continuous plasma interferes detrimentally with the laser produced pulsed photoplasma which is pure. Hence there is a need to remove the plasma before it flows to the photoplasma region. In this paper we describe the studies on extraction of zirconium plasma by electrostatic field in parallel-pate geometry. It was observed that with increase of electron-beam current, the extractor plates were charged by the scattered electrons. This resulted in development of a negative voltage across the plates. However with the onset of melting and production of plasma, this voltage was reduced to zero.