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EFD-C(10)06/13

H-mode Threshold Studies in Helium-4 JET Plasmas

G. Calabrò, D.C. McDonald, M. Beurskens, C.F. Maggi, I. Day, E. de la Luna, T. Eich, N. Fedorczak, D. Frigione, O. Ford, E. Giovannozzi, C. Giroud, P. Gohil, T.P. Kiviniemi, M. Lennholm, P.J. Lomas, J. Lonnroth, G.P. Maddison, I. Nunes, V. Pericoli Ridolfini, F. Ryter, G. Saibene, R. Sartori, W. Studholme, E. Surrey, I. Voitsekhovitch, K-D Zastrow and JET EFDA contributors

Abstract. During its low activation phase, ITER must operate with H or He plasmas. To assess ELM loads and commission some systems, it is desirable that part of this operation be in ELMy H-modes. The high L-H power threshold (P_thr) in hydrogen (H) appears to preclude H H-modes on ITER and instead He is seen as the most likely choice. 2001 JET studies found He plasmas had P_thr(He) 1.4 times that of D. At the transition the He plasmas had helium purity (f_He) of 84-94%. 2008 ASDEX Upgrade (AUG) studies (f_He50-80%) found no change in P_thr between D and He plasma. It should be underlined that previous AUG results showed P_thr(He) 1.4 times that of D. Finally, 2009 DIII-D studies (f_He95%) found He plasmas had P_thr1.3-1.5 times that of D. This paper presents results from the 2009 JET He campaign aimed to better assess He H-mode threshold by studying the impact of f_He and electron density (n_e) on Pthr.

Preprint of Paper to be submitted for publication in Proceedings of the 37th EPS Conference on Plasma Physics, Dublin, Ireland. (21st June 2010 - 25th June 2010)

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