Speaker: George R. McKee, with UW-Madison

Title: Turbulence in Magnetically Confined Plasmas: The What, Why, Where, When and How  

Abstract: Turbulence is a ubiquitous phenomenon in magnetized plasmas, arising from free energy in density and temperature gradients, flows, magnetic geometry, and other plasma system features. While understanding and characterizing the complexities of turbulence in plasmas is a compelling scientific problem, predicting its effects has significant practical implications for the development of economical high-energy gain fusion energy systems. A range of instabilities have been theoretically predicted and experimentally observed in magnetized plasmas, including ion- and electron-temperature-gradient driven modes, trapped electron modes, kinetic and resistive ballooning modes, and micro-tearing modes. Self-driven flows are also an inherent feature of largely 2D turbulence (where the magnetic field defines an “almost” ignorable coordinate) and are key to nonlinear saturation processes. This turbulence results in cross-field radial transport of particles, energy, and momentum from the plasma core to the boundary at rates that typically exceed the irreducible neoclassical collisional transport by orders of magnitude. A grand scientific challenge for the fusion energy sciences has been to accurately measure and simulate turbulence in modern experiments, and predict confinement properties and energy gain, Q, in fusion plasmas reactors such as ITER and a Fusion Pilot Plant. The necessity of measuring turbulence characteristics, behavior, and dynamics in fusion grade plasmas has led to the development a range of fluctuation diagnostics. This presentation will focus on the development of and measurements from a set of active optical and spectroscopic neutral-beam- based fluctuation diagnostics deployed at the DIII-D National Fusion Facility that measure density, temperature and velocity perturbations arising from turbulence and other instabilities in fusion-grade plasmas. These measurements have significantly increased our understanding of turbulence and its parametric scaling behavior in magnetized plasmas and are used to validate models of turbulence through comprehensive comparisons with advanced simulations.

Bio: Dr. George McKee is a Senior Research Physicist with the University of Wisconsin-Madison and performs research at the DIII-D National Fusion Facility in San Diego. His research focuses on understanding the nature of turbulence, turbulent transport and related instabilities in magnetically confined toroidal plasmas and developing optical fluctuation diagnostics to probe turbulence and other plasma instability phenomena. He leads and contributes to diagnostic and research collaborations on the NSTX-U spherical torus facility at the Princeton Plasma Physics Laboratory, the HL-2A & HL-3 tokamaks at the Southwestern Institute of Physics (Chengdu, China), and the W7-X Stellarator (Greifswald, Germany). He mentors numerous graduate students at the University of Wisconsin-Madison, chairs the US Transport Task Force Executive Committee, is a Co-Leader of the ITER Research Group at the DIII-D National Fusion Facility, and is a fellow of the American Physical Society.

This talk will be offered in a hybrid format. If you wish to participate remotely, please send an email to [email protected].