Speaker
Kerry David Lawson
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.1034.pdf
An exploration of a low temperature regime in EDGE2D-EIRENE simulations
of JET ITER-like wall L-mode discharges
K D Lawson1, M Groth2, D Harting1, S Menmuir1, D Reiter3, S Brezinsek3, G Corrigan1,
C F Maggi1, A G Meigs1, S Wiesen3 & JET Contributors*
EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK
1
CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK
2
Aalto University, Otakaari 1, Espoo, 02150, Finland
3
Forschungszentrum Jülich Gmbh, Institut für Energie- und Klimaforschung – Plasmaphysik, 52425
Jülich, Germany
JET with its ITER-like wall (ILW) of Be in the main chamber and W in the divertor is ideally
suited to gain understanding of the behaviour of the plasma edge and divertor, which is essential
for predicting the performance of next-step machines such as ITER. Simulations by Groth et al.
[1] of L-mode discharges run during JET-ILW campaigns and the previous JET-C campaigns, in
which the plasma-facing surfaces were predominately C, have consistently shown a shortfall in
the radiated power below that measured by bolometry, this bringing into question the predictions
for the radiated power and cooling of a radiative divertor in a next step-machine. A similar result
is found for unseeded ELMy H-mode discharges by Järvinen et al. [2]. A series of JET-ILW L-
mode discharges, which reach detachment, provide a stringent test of the simulations in that most
(~90%) of the radiated power from the divertor is due to atomic and molecular D, with impurities
only playing a small role. In EDGE2D-EIRENE simulations, the molecular contribution is,
typically, only ~10-15% and these results suggest that the simulated Te is too high throughout the
divertor volume, in particular not reaching the very low Te (~1eV) required to give significant
atomic D radiative recombination and high molecular densities with their associated power
losses, this being especially so near the inner divertor target [3]. To test the sensitivity of the
simulated temperature to the atomic and molecular power loss terms, these were artificially
varied. A sensitivity to small changes (a few per cent) in the atomic power loss term, within the
expected accuracy of the controlling atomic physics, was found to lead to a step down or
transition in the temperature with increasing power loss [4]. This low temperature regime is
explored by determining the temperature sensitivity to the power losses within particular
temperature ranges. To understand better the acceptable variation of the D emission at different
temperatures a reassessment of the D atomic data has been carried out, in particular to determine
the likely accuracy of the data relating to collisional excitation, ionization and recombination.
When combined with recently completed sensitivity calibrations for a VUV survey and a
poloidally scanning VUV spectrometer [5] they will enable line-of-sight measurements of D line
emission and consequently the power radiated by D to be estimated. The use of ratios of the line
emission from low n shells, which measured along a divertor view are experimentally found to be
independent of temperature, together with the absolute measurements of the D radiation and line
intensities will be used to guide the simulations in order to achieve a more satisfactory agreement
with the bolometric measurements of radiated power.
[1] Groth et al., 2013, Nuc. Fus., 53, 093016 [2] Järvinen et al., 2015, JNM, 463, 135
[3] Lawson et al., 2015, JNM, 463, 582 [4] Lawson et al., 2017, NME, 12, 924
[5] Lawson et al., 2012, Rev. Sci. Instrum, 83, 10D536
*See the author list of X. Litaudon et al., 2017, Nucl. Fusion, 57, 102001
