Impurity behaviour during ECH in the Texas experimental tokamak

During electron cyclotron heating in the Texas Experimental Tokamak, the concentration of metallic impurities near the plasma center increased. In the experiment, a 60 GHz predominantly 0-mode wave was launched from the low-field side of the tokamak plasma. Approximately 100 kW (equivalent to 1/3 of the OH power) was deposited within a few centimeters of the plasma major radius. From analysis of the impurity behavior, it appears that the ECH induced both a substantial increase in the edge impurity source and a modest reduction in the inward impurity transport. Specifically, the edge source was increased by as much as 40%, while for p>0.7, the impurity diffusion was increased by 50%. The enhanced impurity diffusion occurs simultaneously with a reduction in particle confinement and with an increase in plasma potential. (author). 3 refs, 4 figs