April 4-6

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Author: Michael R Halfmoon
Requested Type: Consider for Invited
Submitted: 2022-03-03 13:12:50

Co-authors: D. Hatch, M. Kotschenreuther, S. Mahajan, A. Nelson, E. Kolemen, F. Laggner, A. Diallo, E. Hassan, M. Curie, and R. Groebner

Contact Info:
University of Texas at Austin
2515 Speedway Ave
Austin, TX   78712
United States

Abstract Text:
There remain multiple candidate mechanisms accounting for transport across the H-mode pedestal, including microtearing modes (MTM), ion temperature gradient modes / trapped electron modes (ITG/TEM), electron temperature gradient (ETG) modes, and kinetic ballooning modes (KBM). In this study, gyrokinetic simulations are performed for DIII-D discharge 174082 using the GENE code with inputs from equilibrium profiles reconstructed from experimental data. Local nonlinear simulations have shown that electron heat flux has contributions from ETG-driven transport, but not at the level required to fully satisfy power balance, even with variations to the background profiles. MTMs are identified in both linear gyrokinetic simulations and magnetic fluctuation data, providing an additional mechanism to account for electron heat transport. Neoclassical transport is investigated to account for the remaining observed energy losses in the ion channel. The MTM instabilities found in simulations of a DIII-D discharge are consistent with observed magnetic fluctuations, having frequencies in the electron diamagnetic direction and in the expected range as calculated from equilibrium gradients. Modifying the equilibrium βe can result in MHD-like modes becoming the most unstable linear global mode, with ”fingerprints” that are distinct from MTM’s. We investigate magnetic field and density fluctuations for both MHD-like modes and MTMs in an effort to establish a useful ”fingerprint” for distinguishing these two modes in both simulations and experiments. We investigate the structure and underlying physics of this MHD-like instability. Cross-code comparisons between simulation fingerprints are performed for each set of instabilities. Work supported by US DOE under DE-FC02-04ER54698, DE-FG02-97ER54415, and DE-AC02-09CH11466.