Impurity Transport Studies on LHD

Abstract

The preliminary results of impurity transport studies in the Large Helical Device (LHD) by means of a newly developed the Stellarator Impurity Transport code SIT STRAHL [1] are reported. The attenuation of the emission lines from the ionized Ti ions, launched in the plasma edge by means of the TESPEL injector has been numerically simulated and compared with experiment. In the case of low plasma density discharges with positive radial electric field the outward directed neoclassical drift determines a low confinement time of the Ti impurity ions. The SX-ray emission signal can be reproduced fairly well, indicating the neoclassical nature of Ti ions behavior. In the case of high density regimes with a negative value of the electric field the increase of the confinement time seems not to be able to be explained only by neoclassical transport. The importance of radial electric field on impurity behavior is analyzed and impurity accumulation within the externally induced island is simulated.