Impurity injection experiments and studies on impurity transport behaviour on the HL-1 tokamak

Impurity transport has been studied on the HL-1 tokamak under the conditions of normal Ohmic discharge and H mode discharge induced by a biasing electrode. The experimental results of impurity gas injection and simulation analysis of impurity transport in both discharges are presented. The experimental results show that the impurity confinement is much better in the H mode plasma induced by a biasing electrode than that in the normal Ohmic plasma. The impurity transport simulation results indicate that in both the normal Ohmic plasma and the H mode plasma induced by a biasing electrode, compared with neoclassical theory, the impurity transport coefficient is so high that the impurity transport is anomalous. The concept of 'barrier' is introduced to account for impurity transport becoming longer in the H mode plasma. The phenomena of impurity radiation with longer rise time and slower decay time can be explained reasonably