H-mode Threshold Studies in Helium-4 JET Plasmas
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 (Pthr) 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 Pthr(He) 1.4 times that of D. At the transition the He plasmas had helium purity (fHe) of 84-94%. 2008 ASDEX Upgrade (AUG) studies (fHe 50-80%) found no change in Pthr between D and He plasma. It should be underlined that previous AUG results showed Pthr(He) 1.4 times that of D. Finally, 2009 DIII-D studies (fHe 95%) found He plasmas had Pthr 1.3-1.5 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 fHe and electron density (ne) on Pthr.