Accounting of the power balance for neutral-beam heated H-mode plasmas in NSTX

Power balance accountability was investigated for neutral beam heated plasmas in NSTX. Measurements of heat to the divertor strike plates and radiation in the divertor and the core were made as a function of heating power in lower single-null (LSN) and double-null (DN) configurations. Up to 70% of the net input power is accounted in the LSN discharges with ≈15-20% of power lost as fast ions, ≈25-35% incident on the divertor plates, ≈5% radiated in the core, and ≈5-10% radiated in the divertor. In DN discharges, the fast ion loss is comparable to LSN discharges, the core radiated power fraction is ≈10%, and the power deposited in the lower divertor as radiation and heat flux is ≈20-25% of the total. Assuming up/down symmetry, the power accountability in DN is ≈85-90%.