Real time boronization experiments in CHS and scaling for LHD

Abstract

As a promising wall-conditioning technique in LHD under steady-state high magnetic fields with superconducting magnets, real time boronization (RTB) by puffing decaborane B 10H 14 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 decaborane is efficient to reduce plasma impurities such as oxygen and metals, resulting in expansion of the operating region of the plasma density and stored energy. The puffing at the inside of the LCFS gives better results on RTB than the outer. Even after RTB on the wall at the room temperature, hydrogen recycling does not increase probably due to the small consumed amount with a high plasma heating power used. The operative RTB parameters expected in LHD are estimated using the first scaling of boronization on the device size.