Power deposition in the JET divertor during ELMs

The power deposited in the JET divertor during ELMs has been evaluated using an infrared camera specifically designed for fast measurements. The first results [E. Gauthier, A. Charkin, S. Clement et al., Proc. 24th Euro. conf on contr. Fusion and Plasma Phys., Berchtesgaden, 1997 (European Physical Society, 1998), vol. 21A, p. 61.] indicated that during type I ELMs, surface temperatures in excess of 2000 degrees C were measured, leading to peak power fluxes in the order of 4 GW/m(2). The time integrated power flux exceeded the measured plasma energy loss per ELM by a factor of four. The reasons for this discrepancy are studied in this paper. Redeposited carbon layers of up to 40 mu m have been found on the divertor surface in the places where the highest temperatures are measured. The impact of such layers on the power flux evaluation has been studied with numerical calculations, and a controlled simulation of ELM heating has been performed in the JET neutral beam test facility. It is found that neglecting the existence of layers on the surface in a 2D calculation can lead to overestimating the power by a factor of 3, whereas the error in the calculation of the energy is much smaller. An energy based calculation reduces the peak power during type I ELMs to values around 1.2 GW/m(2). (C) 1999 JET Joint Undertaking, published by Elsevier Science B.V. All rights reserved.