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(EXP5/21) Progress in Quantifying the Edge Physics of the H-mode Regime in DIII-D

R. J. Groebner¹⁾, D. R. Baker¹⁾, J. A. Boedo²⁾, K. H. Burrell¹⁾, T. N. Carlstrom¹⁾, R. D. Deranian³⁾, E. J. Doyle⁴⁾, J. R. Ferron¹⁾, P. Gohil¹⁾, G. R. McKee⁵⁾, R. A. Moyer²⁾, C. L. Rettig⁴⁾, T. L. Rhodes⁴⁾, D. M. Thomas¹⁾, T. H. Osborne¹⁾, and W. P. West^1)
 
1) General Atomics, San Diego, California USA
²⁾ University of California-San Diego, La Jolla, California USA
³⁾ Cardiff University, Wales
⁴⁾ University of California-Los Angeles, Los Angeles, California USA
⁵⁾ University of Wisconsin-Madison, Madison, Wisconsin USA

Abstract.  Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H-mode regime. Electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for such parameters. The quality of H-mode confinement is strongly correlated with the height of the H-mode pedestal for the pressure. The gradient of the pressure appears to be controlled by MHD modes, in particular by kink-ballooning modes with finite mode number n. For a wide variety of discharges, the width of the barrier is well described with a relationship that is proportional to ( $\beta_{\mathrm{p}}^{\mathrm{ped}}$)^1/2. An attractive regime of confinement has been discovered which provides steady-state operation with no ELMs, low impurity content and normal H-mode confinement. A coherent edge MHD-mode evidently provides adequate particle transport to control the plasma density and impurity content while permitting the pressure pedestal to remain almost identical to that observed in ELMing discharges.

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