The impact of fuelling and W radiation on the performance of high-power, ITER-baseline scenario plasmas in JET-ILW
A. R. Field, S. Aleiferis, É. Belonohy, P. Carvalho, I. Coffey, D. Frigione, L. Garzotti, L. Horváth, Hyun-Tae Kim, M. Lennholm, E. Lerche, P. Lomas, C.G. Lowry, J. Mailloux, F. Rimini, C.M. Roach, M. Sertoli, Ž. Štancar, G. Szepesi, D. Van Eester
Abstract
Abstract Sustained operation of high-performance, ITER-baseline scenario plasmas at the high levels of input power ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>≲</mml:mo> </mml:mrow> <mml:mn>40</mml:mn> <mml:mrow> <mml:mtext>MW</mml:mtext> </mml:mrow> </mml:math> ) required to achieve ∼15 MW of D-T fusion power in JET-ILW requires careful optimisation of the fuelling to avoid an unacceptable disruption rate due to excessive radiation, primarily from W impurities, which are sputtered by edge-localised modes (ELMs) from the divertor targets. By using a train of ELM-pacing pellets from a high-frequency pellet injector to promote regular ELMs, which flush W and other impurities from the confined plasma, such high-performance plasmas can be sustained (for ∼5 s) while maintaining a high normalised confinement factor H 98, y 2 ∼ 1, which would otherwise be degraded by reducing the pedestal confinement if a higher rate of D 2 gas fuelling were used instead of the pellets to mitigate the W contamination. The causes underlying the improved performance and energy confinement obtained using this combined, gas and pellet fuelling scheme is investigated here in some detail.