H-mode and L-H Threshold Experiments During ITER-like Plasma Current Ramp Up/Down at JET with ILW H-mode and L-H Threshold Experiments During ITER-like Plasma Current Ramp Up/Down at JET with ILW

" This document is intended for publication in the open literature. It is made available on the understanding that it may not be further circulated and extracts or references may not be published prior to publication of the original when applicable, or without the consent of the Publications Officer, The contents of this preprint and all other JET EFDA Preprints and Conference Papers are available to view online free at www.iop.org/Jet. This site has full search facilities and e-mail alert options. The diagrams contained within the PDFs on this site are hyperlinked from the year 1996 onwards.. 1 1. IntroductIon ITER plasma scenario studies [1] have shown that the optimisation of the flux consumption from the poloidal field coils requires control of the plasma inductance, used here l i = l i (3) [1]. This control was achieved in ITER demonstration discharges (at DIII-D, C-Mod, AUG and JET-C) using a combination of full bore start up with early X-point formation and current ramp-up in H-mode. H-mode during current decay down has been shown also instrumental to maintain low inductance in order to minimise flux consumption [2]. Moreover variation of plasma inductance in ohmic discharges can be controlled, independently of the plasma current ramp-down rate, by varying the plasma elongation, as reported in [2]. An all-metal ITER-like wall (ILW) [3], consisting of beryllium in the main chamber and tungsten surfaces in the divertor, has now been installed in JET. Its implementation has offered the opportunity to assess if the flux consumption and plasma inductance evolution is modified by Be-wall and W-divertor during the current rise and current decay (e.g. current profile evolution, plasma controllability issues as W accumulation in the transient phase, L-H transition, etc.). Details of the experimental results obtained in 2012 with the ILW and comparison with carbon-fibre reinforced carbon (CFC) wall (JET-C) will be given here. The CRONOS suite of codes has been used to interpret JET-ILW experimental results and make predictions for ITER. 2. ExpErImEntal sEtup. The JET scenario used was 2.5MA/2.4T (q 95 ≈ 3) at low triangularity d ≈ 0.25, low voltage breakdown (E axis »0.37V/m), early X-point formation, with additional heating applied from plasma current I P = 1.5MA. This matches, using the plasma resistivity as guide, as discussed in [1], the proposed baseline inductive scenario for ITER of 15MA/5.3T (q 95 ≈ 3), X-point formation at ~4MA and additional heating applied from I …