University of Texas, Austin
Friday, May 10, 2019
Abstract: The properties of an edge transport barrier are governed by three complex and sensitively interconnected components: (1) pedestal MHD stability, (2) divertor and SOL conditions, and (3) the residual pedestal transport. The residual transport remains, perhaps, the least understood component of the edge system with no general consensus even on the major transport mechanisms at play. Transport, in combination with the corresponding sources and sinks, determines, among other things, the heating power necessary to achieve a given pedestal temperature; the inter-ELM evolution of pedestal density and temperature profiles, which ultimately determines the operating point at which an ELM is triggered; and the accessibility and properties of ELM-free regimes. An understanding of pedestal transport is indispensable to tokamak design, optimization, and operation. This presentation will report on a broad range of gyrokinetic pedestal transport studies including the ongoing FY19 theory performance target (TPT), whose goal is to identify the turbulent transport mechanisms, along with the corresponding heat and particle sources, that govern pedestal dynamics. This being pursued via two sets of computational tools: (1) gyrokinetic codes (GENE and CGYRO), which can analyze the instabilities that arise in the pedestal, and (2) edge codes (SOLPS and UEDGE), which, when operated in interpretive mode, can provide the best possible estimate of particle and heat sources---e.g., the ionization density source and the atomic energy loss channels due to ionization, charge exchange, and radiation. Such information, in combination with available fluctuation data, and observed inter-ELM profile evolution, provides powerful constraints on the candidate instabilities that may govern pedestal transport.
Comparisons will be made with discharges spanning multiple devices and exploring a wide range of parameters, modes of operation, wall materials, etc.. This combined analysis of instabilities / transport and edge modeling is unprecedented and, when applied to a wide range discharges, promises to qualitatively advance our understanding of pedestal transport. Such an understanding is necessary to predict and optimize pedestals in future burning plasma devices. It is, in particular, crucial for understanding and predicting ELM-free regimes, in which transport keeps pedestal profiles away from explosive MHD limits.
Bio: Dr. David Hatch is a research scientist at the Institute for Fusion Studies (IFS) at the University of Texas at Austin. He has made major contributions to understanding turbulent transport in edge transport barriers including the first identification via nonlinear gyrokinetic simulations of the microtearing mode in the H-mode pedestal. He leads the SciDAC Partnership for Multiscale Gyrokinetic (MGK) turbulence, which aims to advance simulation capabilities for frontier fusion turbulent transport problems. Dr. Hatch also leads the DOE-FES 2019 theory performance target, which will identify the major heat and particle transport mechanisms in edge transport barriers over a broad range of experimental conditions. Dr. Hatch received his PhD in 2010 from the University of Wisconsin-Madison, where he identified key nonlinear couplings among linear eigenmodes in gyrokinetic turbulence. During a postdoctoral stay at the Max-Planck Institute for Plasma Physics, he contributed to the understanding of electromagnetic effects in tokamak turbulence. Dr. Hatch also maintains interest in basic aspects of gyrokinetic plasma turbulence and has made contributions to understanding velocity space spectra, phase space scales of energy dissipation, and phase space structures of gyrokinetic turbulence.