L-H threshold results in hydrogen plasmas in JET-ILW*

The ITPA scaling law for the H-mode power threshold, P(L-H), is strongly weighted to a dataset of carbon wall JET (JET-C) discharges. Identical discharges with the Be/W wall (JET-ILW) in deuterium have shown a 30{\%} reduction of P(L-H) and a minimum as function of density, not observed with the current divertor in JET-C [1]. A strong dependence of P(L-H) on the divertor configuration was found, linked to changes in the divertor recycling pattern [2]. Subsequently, an experiment was conducted in hydrogen to investigate the isotope effect on P(L-H) in JET-ILW. P(L-H) is increased by a factor 2 in the high density branch, as expected. Remarkably, ne,min is shifted to higher density. Comparison between the hydrogen and deuterium discharges show the transition occurs at similar values of stored energy and closely matched edge density and temperature profiles. \\[4pt] [1] C.F. Maggi et al., Nucl. Fus. 54 (2014) 023007\\[0pt] [2] E. Delabie et al., proceeding of the 24th IAEA conference, St. Petersburg, Russia (2014).