Abstract Details
Abstracts
Author: Bradley Andrew
Requested Type: Poster
Submitted: 2024-04-11 14:18:55
Co-authors: E.G. Kostadinova, J. Eskew, D.M. Orlov, E.C.Howell
Contact Info:
Auburn University
711 Shelton Lane
Auburn, AL 36830
United States
Abstract Text:
Anomalous diffusion is commonly observed in tokamaks and stellarators in the form of suprathermal or relativistic (runaway) electrons. Those sub-populations of energetic particles lead to the formation of ‘fat’ tails on the velocity distribution functions, which makes them challenging to model. Here we discuss the application of nonextensive statistics to the study of energetic electrons in fusion plasmas. The nonextensive statistics, proposed by Tsallis, is a formulation of statistical mechanics in which the typical functions are power laws, instead of the exponentials traditionally used in the Boltzmann-Gibbs formulation. The nonextensivity feature of the formulation makes it independent of initial conditions and suitable for modeling many-body complex systems with long-range interactions. Tsallis’ statistics has been applied to space physics and dusty plasma, but has not yet been fully adopted in fusion. Here we reconstruct histograms of electron displacements from a particle tracing code using data from the DIII-D and NSTX-U tokamaks. We fit a q-Gaussian distribution to these histograms to exact the nonextensive q parameter. This parameter quantifies how a distribution function deviates from a Gaussian or Maxwellian, which makes it ideal for investigating anomalous diffusion in the form of confined (subdiffusive) or energetic (superdiffusive) electrons. Using the extracted q parameters for different plasma conditions, we check the validity of a proposed analytical expression that relates q to the thermophoretic force and the Lorentz force.
This work is supported by DE-SC0023476, DE-SC0023061, DE-SC0021185
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