The effect of T i /T e ratio on formation and sustainability of LH - PowerPoint PPT Presentation

The effect of T i /T e ratio on formation and sustainability of LH driven low density and RF driven high density ITBs Task Area: Advanced Scenarios Igor Bespamyatnov, Bill Rowan, Ken Liao, Syunichi Shiraiwa, Catherine Fiore, John Rice 1/10/2011 2011 C-Mod Ideas Forum 1

Motivation ASDEX-Upgrade DIII-D JT-60U Motivation: • Presently most of the strong well controlled ITB’s are achieved with high T i /T e ratio. • Temperature gradient modes (anomalous transport) are stabilized with increase of T i /T e . • Fast alpha particles heating predetermines that T i ~T e for ITER. • A few experiments were undertaken on major tokamaks to generate T i < T e and T i ~T e ITBs by applying a mixture of different heating schemes. • Regarding a portability of these results to a fusion reactor plasma, it should be noted that T e ≈ T i has been achieved by a similar heating of electrons and ions and not by collisional heat transfer. 1/10/2011 2011 C-Mod Ideas Forum 2

ITBs at Alcator C-Mod RF-heated , high-n e n e -peaks, T e -doesn’t. LH-heated , low-n e T e -peaks, n e -doesn’t. • Alcator C-Mod can produce: 1. High-density RF heated ITBs at T i ~T e (collisionally equilibrated?) 2. Intermediate density Ohmic ITBs at Ti <~Te (recent results from MP477, W. Rowan) 3. Low density LH heated ITBs at T i < T e . (recent results - MP553, S. Shiraiwa) Will it be possible to consolidate these types of ITB? (Find the similarity and may even study some mixed regimes) Will C-Mod ITBs be a good benchmark for study of ITER ITBs and complexities associated with their formation and sustainability? 1/10/2011 2011 C-Mod Ideas Forum 3

Experimental plan and a run time. Plan: Study the formation and sustainability of ITBs depending on Ti/Te ratio. Opened for suggestions of how to scan ITB performance dependence on Ti/Te ration. One of the option may be the ICRF heating of low density plasmas prior to formation of LH-heated ITB. Effectiveness of ICRF in such low densities is sill a question. Run time (1.5 days): 1. One day for low-density LH ITBs with prior injection of ICRF to increase T i /T e . 2. Half day for high-density RF ITBs. Need to find a way to modify a T i /T e , when n e density and RF power are fixed. 1/10/2011 2011 C-Mod Ideas Forum 4