Effect of a Limiter on Ohmic Discharges in the Heliotron D

Abstract

Ohmic discharges with and without a limiter are being studied in the Heliotron D. Without the limiter, we observe longer containment time and lower impurity concentration than with the limiter, and a stable current with the safety factor $q_{0H}\simeq 0.4$ is obtained. With the limiter, strong current fluctuations are observed near rational values of the rotational transform, i.e., $\frac{\iota }{2\pi }=\frac{({\iota }_F+{\iota }_{0H})}{2\pi }\simeq 0.5 \mathrm{and} 1.0$.