Abstract Details
Abstracts
Author: Bradley R Andrew
Requested Type: Poster
Submitted: 2025-03-13 16:41:48
Co-authors: Jessica Eskew, Dmitri Orlov, E. G. Kostadinova
Contact Info:
Auburn
711 Shelton Lane
Auburn, 36830
USA
Abstract Text:
Anomalous diffusion is commonly observed in tokamaks and stellarators and requires a kinetic or statistical approach to model fully. 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 that makes it possible to model many-body complex systems with long-range interactions, while still being able to model classical Boltzmann statistics. From simulation data of NSTX-U, we reconstruct histograms of polodial magnetic flux and give an analytical representation of its relation with velocity distributions from the currents. We quantify how the flux distributions change during successive bifurcations of magnetic islands caused by nonaxisymmetric coil current (NCC) perturbations. We fit a q-Gaussian distribution to these histograms to extract the nonextensive q parameter, which quantifies how a distribution function deviates from a Gaussian or Maxwellian. Assuming electrons are highly magnetized and closely follow the magnetic field lines, we use these fits to predict the evolution of electron diffusion from confined (subdiffusive) to classical and eventually energetic (superdiffusive) processes as the NCC perturbation is increased. We conjecture that the crossover to a superdiffusive process is caused by an increased stochasticity of the magnetic field after successive island bifurcations. We quantify stochasticity in three ways: (i) quantifying disorder of the simulated electron trajectories, (ii) calculating the Chirikov parameter, and (iii) modeling manifold tangles around island X-points.
Characterization: 1.0
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