Abstract
Global power balances are investigated for neutral-beam heated divertor discharges in ASDEX. In high-density discharges ( n e ≈ 8×10 13 cm −3 ) bolometrically detected volume power losses in the divertor remain the predominant loss channel when the total heating power is raised from 0.4 MW to more than 2 MW. About 80% of the heating power flows into the divertor. The fraction thereof lost by radiation grows exponentially with n e and attains maximum values of nearly 50% of the heating power. Between 30 and 40% of the input power is missing in the global balance, and this fraction increases when changing from the L to the H mode of neutral injection. As in the ohmic heating case, divertor radiation can mainly be attributed to neutral hydrogen atoms during neutral injection. The temperature dependence of divertor radiation — an approximately linearly increasing function of temperature — indicates that in addition to Franck-Condon dissociation of H 2 molecules resonant charge exchange of H atoms significantly contributes. Power deposition profiles on the neutralizer plates are measured by a thermographie system with a time resolution of 0.4 ms.
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