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

The effect of Ti/Te 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

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Motivation

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Motivation:

• Presently most of the strong well controlled ITB’s are achieved with high Ti/T

e ratio.

• Temperature gradient modes (anomalous transport) are stabilized with increase of Ti/T

e.

• Fast alpha particles heating predetermines that Ti ~T

e for ITER.

• A few experiments were undertaken on major tokamaks to generate Ti < T

e and Ti ~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

Te ≈ Ti has been achieved by a similar heating of electrons and ions and not by collisional heat transfer. JT-60U DIII-D ASDEX-Upgrade

ITBs at Alcator C-Mod

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• Alcator C-Mod can produce:
• 1. High-density RF heated ITBs at Ti ~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 Ti < 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? RF-heated , high-ne ne-peaks, Te-doesn’t. LH-heated , low-ne T

e-peaks, ne-doesn’t.

Experimental plan and a run time.

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Run time (1.5 days):

• 1. One day for low-density LH ITBs with prior injection of ICRF to increase Ti/T

e.

• 2. Half day for high-density RF ITBs. Need to find a way to modify a Ti/T

e, when

ne density and RF power are fixed. 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.