The heating of thermonuclear plasmas by the injection of accelerated particles has become a favoured method during the last few years. One of the problems involved is to achieve beams of comparatively high flux densities. As space charge is the physical barrier which limits the flux density of charged particle beams, cluster ions with low charge-to-mass ratio are expected to be an appropriate means to diminish this difficulty. A second property of the clusters is their broad mass distribution

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... e to their statistical growth process. Since all clusters have the same energy after being singly ionized and accelerated the mass distribution is transformed into a velocity distribution. This in turn should be useful to counteract the growth of plasma instabilities. To study the interaction of clusters with a plasma the Max-Planck-Institut für Plasmaphysik, Garching (IPP) and the Institut für Kernverfahrenstechnik, GfK Karlsruhe (IKVT) agreed that a cluster injector should be developed by the IKVT and finally transferred to the IPP for injection experiments on the Wendelstein VII-Stellarator. To provide a relevant amount of beam power for heating the W VII-plasma the design data of the cluster-injector are: 10 A equivalent beam cur 2 ent of neutral hydrogen atoms, 1 MV accelerating voltage, 10 hydrogen atoms per cluster mean size of the singly ionized clusters corresponding to a beam power of 100 kW. The high voltage generator is almost completed and available for preliminary experiments on the high gradient acceleration of cluster ions at the Institute of Nuclear Physics of the University of Lyon. The injector structure and the cryostat for the cluster beam source will be manufactured by industry during the next two years. In the meantime the ionizer of the 10 A equivalent cluster beam will be developed by IKVT and experiments dealing with the neutralization of 1 MeV cluster ion beams will be carried through with the low current 1 MV accelerator of the Institut für Aerobiologie (IFA) of the Fraunhofer Gesellschaft in Grafschaft, Germany.