Impact of minority concentration on fundamental (H)D ICRF heating performance in JET-ILW

Abstract

ITER will start its operation with non-activated hydrogen and helium plasmas at a reduced magnetic field of B 0 = 2.65 T. In hydrogen plasmas, the two ion cyclotron resonance frequency (ICRF) heating schemes available for central plasma heating (fundamental H majority and 2nd harmonic 3 He minority ICRF heating) are likely to suffer from relatively low RF wave absorption, as suggested by numerical modelling and confirmed by previous JET experiments conducted in conditions similar to those expected in ITER's initial phase. With 4 He plasmas, the commonly adopted fundamental H minority heating scheme will be used and its performance is expected to be much better. However, one important question that remains to be answered is whether increased levels of hydrogen (due to e.g. H pellet injection) jeopardize the high performance usually observed with this heating scheme, in particular in a full-metal environment. Recent JET experiments performed with the ITER-like wall shed some light onto this question and the main results concerning ICRF heating performance in L-mode discharges are summarized here.

N=2 ICRH of H majority plasmas in JET-ILW

“…Generally speaking, ICRH gives rise to higher bulk radiation (b) and W content (c) than NBI heating and both quantities increase linearly with the input ICRF power. The radiated fraction with ICRH is only about 20%, which is comparable to the values observed in N=1 ICRH scenarios in similar conditions [8]. Some NBI points exhibit unusually high radiation and X[W] values and are associated to transient impurity events (see the large error bars).…”

Parameter study of ICRH wave propagation in IShTAR

“…Ion cyclotron resonance heating (ICRH) -also often referred to as radio frequency (RF) heating in view of the fact that for typical magnetic field strengths of current-day fusion machines the ion cyclotron frequency lies in the MHz range of frequencieshas proven to be a very reliable method to heat plasmas in tokamaks to fusion-relevant temperatures (Noterdaeme et al 2008;Bobkov et al 2013;Lerche et al 2014a). By properly choosing the system parameters (adopting the relevant driver frequency and designing the antenna to have a desired antenna spectrum), ICRH allows heating of the core of large, dense plasmas in large machines.…”

“…Moreover, the power carried by the slow wave sloshes around in the edge. As a consequence, subpopulations of particles can resonantly or non-resonantly be accelerated by ICRH waves close to launching structures, causing hot spots and sputtering (Klepper et al 2013;Jacquet et al 2014;Lerche et al 2014a;Ochoukov et al 2014). Also, static electric fields set-up through the net effect of the rapidly varying field and giving rise to wave-induced density modifications are thought to be co-responsible for experimentally observed wave-induced hot spots.…”

Accelerating the convergence of a tokamak modeling code with Aitken’s method

“…A simple example loosely inspired by JET is used [36][37][38]; different values of χ and the launched power P launched have been tested.…”