LARGE-AREA RADIO-FREQUENCY PLASMA SOURCES FOR FUSION APPLICATIONS

Four powerful inductively coupled radio frequency (rf) plasma generato rs producing 90 A, 55 kV hydrogen beams were manufactured for the seco nd injector of ASDEX Upgrade. The design of the source and the power s upply was optimized based on the experience with a prototype source. D uring conditioning of the first two sources, it was demonstrated that power efficiency, transmission of the beam power and reliability meet all requirements. The start of the neutral beam injection with the sec ond injector is scheduled for October 1997. Recently, also negative io ns in rf sources sire being investigated within a collaboration with C EA Cadarache. In this development project a positive ion prototype rf source is being utilized with a small extraction area (48 cm(2)) and a 700 G cm magnetic filter. Without cesium a current density of 4.5 mA/ cm(2) was achieved so far at elevated pressure (1.6 Pa), the H--curren t density being proportional to the rf power. At medium pressure (0.6 Pa) the current density is lower approximately by a factor of 5, but p reliminary results with cesium injection show a relative increase by a lmost the same factor in this pressure range. Probe measurements indic ate electron temperatures of 2.5-4.5 eV close to the plasma grid. Atte mpts to improve the performance by better plasma confinement, differen t wall materials, and filter strengths are under way. (C) 1998 America n Institute of Physics.