THE TOROIDAL BELT PUMP LIMITER, ALT-II, IN THE TEXTOR TOKAMAK

A toroidal belt pump limiter has been designed, constructed, installed and operated in the TEXTOR tokamak. The Advanced Limiter TEST-II, or ALT-II, is carried out as a partnership under a joint agreement between the European Community, Japan and the United States. ALT-II is designed to withstand the high heat fluxes (greater than 500 W/cm2) intrinsic to the boundary region of tokamak plasmas while simultaneously removing 5% to 10% of the core plasma efflux. The belt consists of eight segments, each 28 cm wide, 150 cm long, and 1.2 cm thick, and each is covered with shaped graphite tiles. Mounted behind each blade is a "scoop" system which captures plasma flowing past the leading edges and behind the blades. This plasma neutralizes on a collector plate and the resulting neutral gas is pumped. During ohmic discharges, 50 to 60 A of current is collected in the scoops and removal rates up to 0.25 Torr-1/s are achieved. The blades are instrumented with Langmuir probes and thermo couples, and other diagnostics include infrared cameras, H-alpha-monitors, pressure gauges, helium charge exchange spectroscopy, and helium gas diagnostics. The plasma edge and the operation of the pump limiter system are described.