Heat Transport Driven by Electron Temperature Gradient Modes in Tokamak Plasmas

T. Rafiq, C. Wilson, E. Schuster

11th ITER International School on “ITER Plasma Scenarios and Control”

San Diego, California, USA, July 25-29, 2022

A new model for the electron temperature gradient (ETG) modes is developed for tokamak plasmas. This model is based on two-fluid reduced Braginskii equations that govern the dynamics of low-frequency short-wavelength electromagnetic toroidal ETG driven drift modes. The low collisionality NSTX discharge is used to scan the plasma parameter dependence on the ETG real frequency, growth rate, and electron thermal diffusivity. Sub-critical transport due to ETG modes is discovered in the core region where modes have more electromagnetic characteristics. Several previously reported gyrokinetic trends are reproduced, including the stabilizing effects of steep temperature and density gradients, reverse magnetic shear, large β and gradient of β, large collisionality, destabilizing effects of safety factor and stabilizing and destabilizing effects of toroidicity, where β is the ratio of plasma pressure to the magnetic pressure. The electron heat diffusivity associated with the ETG mode is discovered to be on a scale consistent with the experimental diffusivity determined by power balance analysis. The developed ETG model will be employed as a component of the Multi-Mode anomalous transport module in the integrated modeling code TRANSP to predict a time dependent electron temperature profile in conventional and low aspect ratio tokamaks.

*This research is supported by the U.S. Department of Energy, Office of Science, under Award Numbers DE-SC0013977 and DE-SC0021385.