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ITB formation – Ti critical gradient dependence

ITB formation – Ti critical gradient dependence. K. Zhurovich, M. Greenwald, C. Fiore, P. Bonoli, D. Ernst, A. Hubbard, J. Rice. Motivation To understand triggering mechanism for ITBs Can ITB formation be explained in the framework of suppressing ITG turbulence via increasing L T Goal

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ITB formation – Ti critical gradient dependence

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  1. ITB formation – Ti critical gradient dependence K. Zhurovich, M. Greenwald, C. Fiore, P. Bonoli, D. Ernst, A. Hubbard, J. Rice • Motivation • To understand triggering mechanism for ITBs • Can ITB formation be explained in the framework of suppressing ITG turbulence via increasing LT • Goal • Make careful measurements of electron (with all available diagnostics) and ion (HIREX) temperature profiles at the onset of ITBs • Investigate sensitivity of LT to power deposition • Extrapolate to ITB threshold

  2. ITB dependence on RF resonance location • Whether or not we can create ITBs strongly depends on the B-field with small (if any) hysteresis • Suggests strong dependence on the RF resonance location • Moving RF resonant location changes temperature profile, and if the conditions are close to marginal stability this might explain the observed dependence

  3. Plan • Use one frequency RF (80 MHz - to have all ECE diagnostics) • Scan RF resonance location on shot-to-shot basis by changing B-field (5.4T  6.2T) • Reduce other effects: keep q and total RF power constant • Estimate how much Ti can deviate from Te (assume Ti=Te?) • For each shot calculate LT at different locations • Seek dependence of LT on RF resonance location, look for Lcrit • Make stability analysis using GS2 code, look for strong dependence of ITG turbulence suppression on the LTLcrit

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