OUTGASSING MEASUREMENT OF THE WAVE-GUIDE MODULE FOR A STEADY-STATE LHCD ANTENNA

An outgassing rate is measured using a waveguide module during a long pulse r.f, injection at 3.7 GHz in order to operate a lower hybrid cur rent drive (LHCD) antenna in steady state. The waveguide module consis ts of four sub-waveguides which are made of dispersion-strengthened co pper and copper-plated stainless steel with cooling channels to contro l its working temperature between 100 and 500 degrees C. The waveguide module shows the high power capability of power density up to 200 MW m(-2) after short term conditioning. A low outgassing rate of about 2 x 10(-7) Pa m(3) s(-1) m(-2) is obtained during r.f. injection up to 1 50 MW m(-2) at a working temperature of T = 300 degrees C after 450 de grees C baking. Long pulse r.f. injection is effective for reduction o f the outgassing by about 1/100. Outgassing during r.f. injection depe nds on the working temperture but is independent of the r.f. power den sity after sufficient conditioning. The calculation code taking desorp tion, adsorption and diffusion processes into account can show time be havior of outgassing in the waveguide module. A quasi-constant outgass ing of about 10(-7) Pa m(3) s(-1) m(-2) is observed at a power density of 150 MW m(-2) in 1800 s injection while keeping a saturated tempera ture at the center of the module below 120 degrees C by using water co oling. The outgassing properties obtained indicate that steady state o peration of an LHCD antenna is feasible without a large pumping system .