Engineering brochure explains planar plasma deposition system

Abstract

Cluster beams are of growing interest in plasma physics for heating and fueling fusion devices. At the Institute of Nuclear Engineering of the Karlsruhe Nuclear Research Centre an injector is under construction, which aims at the production of high power beams of electrically accelerated cluster ions of hydrogen.A hydrogen cluster is a condensed aggregate of molecules held together by the van der Waals forces. A cluster beam is obtained by rapid expansion of gaseous hydrogen from a cooled nozzle into vacuum. The outstanding properties of cluster beams are their high particle flux densities, an almost uniform particle velocity, a very sharp spatial limitation and a broad distribution of the particle size.An essential part for cluster beam generation is, besides the expansion nozzle and proper stagnation conditions, an adequate pumping system for the extreme gas load which occurs in cluster beam formation. The portion of cluster beam amounts to about 10% of the entire nozzle mass flux; therefore, 10 times of the cluster beam mass flow have to be disposed of. A cluster beam of 100 A equivalent current (= 10 torr l/s−1) calls for a pumping capacity of 100 torr 1/s−1 at a pressure of about 10−4.A cryosystem using liquid helium is described which provides the necessary pumping speed by cryopumps. The same cryostat yields also a cryogenic capacity for nozzle cooling and, in the case of the cluster injector mentioned above, the pumping speed required for the ionization regime and the accelerating tube.The production of intense cluster beams, cryopumping under extremely high gas load and typical properties of the cluster beams source with integrated cryopumps are discussed.