REAL-TIME BORONIZATION EXPERIMENTS IN CHS AND SCALING FOR LHD

As a promising wall-conditioning technique in LHD under steady-state h igh magnetic fields with superconducting magnets, real time boronizati on (RTB) by puffing decaborane B10W14 into the main NBI-heated plasma has been first examined in CHS. It is shown that, as compared with the usual glow discharge method, only the 2 orders smaller amount of deca borane is efficient to reduce plasma impurities such as oxygen and met als, resulting in expansion of the operating region of the plasma dens ity and stored energy. The puffing at the inside of the LCFS gives bet ter results on RTB than the outer. Even after RTB on the wall at the r oom temperature, hydrogen recycling does not increase probably due to the small consumed amount with a high plasma heating power used. The o perative RTB parameters expected in LHD are estimated using the first scaling of boronization on the device size.