Testing predictions of electron scale pedestal turbulence in DIII-D H-modes

Walter Guttenfelder

Princeton Plasma Physics Laboratory

Friday, May 3, 2019

3:00pm

NW17-218

PSFC Seminars

Abstract: This talk will present experimental and gyrokinetic analysis of transport in the edge pedestal region of DIII-D ELMy H-mode discharges. The analysis is performed for two discharges with different divertor geometry to clarify the role of transport vs. sources in setting the pedestal density and temperature profiles. Nonlinear electron-scale gyrokinetic simulations in the sharp gradient region predict that electron temperature gradient (ETG) turbulence can produce significant electron heat flux compared to the observed heat flux. On the other hand, neoclassical transport provides a significant contribution to the experimentally inferred electron particle flux. Additional nonlinear ETG simulations are performed to predict the sensitivity of both electron thermal and particle transport contributions to input gradients. A pedestal-ETG transport model is derived using an analytic fit to the simulation results that follows theoretical expectations. The pedestal-ETG model is used in addition to neoclassical theory to predict both ne and Te pedestal profiles. Although ETG and neoclassical transport play important roles in setting these profiles, the modeling suggests an additional transport mechanism may be required to match experimental profiles.

Bio: Walter Guttenfelder is a research physicist at PPPL and head of the NSTX-U Transport and Turbulence topical science group. His expertise is centered on validation of turbulent transport simulations and models in the core and edge region of toroidal magnetic confinement devices. During his time at PPPL he has focused on core transport in high-beta, low-aspect-ratio spherical tokamaks (NSTX, MAST), which requires measuring and simulating “non-traditional” tokamak drift wave turbulence mechanisms (e.g. MTM, KBM, ETG as opposed to ITG/TEM, for those familiar with the zoology of drift wave acronyms). Walter began investigating ST transport during post-docs at University of Warwick (UK) and PPPL. Prior to focusing on tokamaks, he was a graduate student at the University of Wisconsin-Madison where he performed experiments, simulations and modeling to diagnose trapped electron mode transport and turbulence in the world’s first quasi-symmetric stellarator (HSX). His most recent work focuses on investigating the role of electron scale turbulence in the edge pedestal region of DIII-D and NSTX H-modes.