Accounting of the Power Balance for Neutral-beam-heated H-Mode Plasmas in NSTX
Authors: S.F. Paul, R. Maingi, V. Soukhanovskii, S.M. Kaye, H. Kugel, and the NSTX Research Team
Date of PPPL Report: August 2004
Presented at: the 16th International Conference on Plasma Surface Interactions in Controlled Fusion (PSI16), 24-28 May 2004, in Portland, Maine. To be submitted to Journal of Nuclear Materials.
A survey of the dependence of power balance on input power, shape, and plasma current was conducted for neutral-beam-heated plasmas in the National Spherical Torus Experiment (NSTX). Measurements of heat to the divertor strike plates and divertor and core radiation were taken over a wide range of plasma conditions. The different conditions were obtained by inducing a L-mode to H-mode transition, changing the divertor configuration [lower single null (LSN) vs. double-null (DND)] and conducting a NBI power scan in H-mode. 60-70% of the net input power is accounted for in the LSN discharges with 20% of power lost as fast ions, 30-45% incident on the divertor plates, up to 10% radiated in the core, and about 12% radiated in the divertor. In contrast, the power accountability in DND is 85-90%. A comparison of DND and LSN data show that the remaining power in the LSN is likely to be directed to the upper divertor.