Imaging runaway electron distribution functions in tokamaks

Carlos Paz-Soldan

General Atomics

Friday, December 2, 2016

11:00am

NW17-218

PSFC Seminars

Abstract: Uncontrolled plasma shutdowns in tokamaks have the potential to generate intense beams of relativistic (multi-MeV) “runaway” electrons, which if not safely dissipated pose a severe risk to the integrity of plasma-facing components.  These beams are distributed in physical space as well as in phase space, presenting complex dependencies for both theory and experiment.  A new diagnostic capable of resolving these multi-dimensional distributions has recently been deployed on the DIII-D tokamak.  Called the “gamma-ray imager” (GRI), this diagnostic employs multi-view pulse-height counting of bremsstrahlung-emitted gamma rays from the relativistic electrons.  This seminar will introduce the diagnostic, describe its first measurements of relativistic electron distributions and their dependence on plasma parameters, and finally discuss how these measurements will help validate theoretical models of relativistic electron control for extrapolation to burning plasmas.

Bio: Carlos Paz-Soldan is a scientist with the DIII-D national fusion program at General Atomics, in San Diego, California.  He completed his bachelor’s degree in Engineering Physics at Queen’s University in Canada, and became interested in plasmas and fusion after a colloquium given there by Amanda Hubbard (also her Alma Mater).  Carlos pursued his PhD at the University of Wisconsin-Madison and graduated in 2012.  His thesis work was done under Prof Cary Forest and Chris Hegna, and centered on the effect of differentially rotating conducting walls on MHD stability – actually an experimental project! He was awarded the Marshall Rosenbluth Outstanding Doctoral Thesis prize for his work.  Since 2012 he has been a member of the DIII-D program and divides his time between inductive scenario development, optimization of 3D magnetic fields, and understanding of runaway electron dynamics.  He gave a colloquium here at MIT two years ago on 3D field topics, and is happy to return and discuss his efforts on runaways.