Study of RF plasma emitter for the ion source

Summary form only given, as follows. The radio frequency discharge, when used in ion sources as a plasma emitter, has a number of advantages over the filament and arc discharges. Among these are longer lifetime of the discharge vessel assembly, fast start-up, high reliability, low fraction of the molecular ions in the generated plasma, etc. That is why we have chosen the RF discharge-based plasma emitter for the multiseconds neutral beam injector which is now developed in Budker INP for the diagnostic applications at TEXTOR. In the report, we present the results of the experimental tests of such a plasma emitter. An inductive discharge in hydrogen was effected inside a cylindrical quartz chamber by an RF oscillator with frequency of /spl sime/5 MHz. An axial magnetic field produced by a pair of coils was employed to direct the discharge while its longitudinal profile was varied to achieve the required uniformity of the plasma on the emitting surface. The RF power was inductively coupled to the plasma alternatively by a 6-turns circular coil or a saddle coil both placed around the discharge vessel. Using the first type of inductor we have generated the plasma emitter with uniformity of /spl delta/j/j/spl les/3%, current density of 140 mA/cm/sup 2/ inside of extraction area, of 65 mm in diameter. With the saddle-coil antenna, efficiency of the discharge was considerably higher allowing to produce the ion current density up to 0.7 A/cm/sup 2/ with variation /spl delta/j/j=10% over the entire emitting surface with diameter of 40 mm. In these regimes, the working pressure of hydrogen was 3-4 mTorr. RF power, which absorbed in discharge, was about 3 kW. Also presented in the paper are the first results of tests of the ion source with the RF emitter.