Abstract Details
Abstracts
Author: Evdokiya Kostadinova
Requested Type: Poster
Submitted: 2024-04-12 16:58:07
Co-authors: Bradley Andrew (Auburn), Jessica Eskew (Auburn), Dmitri Orlov (UCSD), Eric C. Howell (Tech-X Corp.), Tyler Cote (GA)
Contact Info:
Auburn University
380 Duncan Drive STE 2158
Auburn, Alabama 36849
United States
Abstract Text:
Here we introduce a spectral approach to the study of anomalous diffusion in magnetically confined fusion plasmas. in scenarios where the magnetic topology includes islands and stochasticity. In these cases, anomalous diffusion is caused by non-local collisions and correlations that lead to populations of energetic and/or sub-diffusive particles. In the spectral approach, correlations and stochasticity are incorporated in a Hamiltonian operator, which uses a fractional Laplacian for the kinetic energy (to model non-locality) and a distribution of random disorders for the potential energy (to model stochasticity). The operator is iteratively applied to an initial energy state to advance the energy in an infinitely-dimensional Hilbert space. In the limit of many iterations, one obtains information on the spectrum of possible energy states for that system, including the probability for continuous spectrum corresponding to extended states. We apply the model to data from frontiers experiments at the DIII-D tokamak, in ~20MeV energy electrons were observed to become confined in magnetic islands and de-confined during island bifurcation. We show that for a Hamiltonian with a sub-diffusive operator and small stochasticity, enhanced probability for transport is expected at scales proportional to the island width. This suggests that electrons can make non-local jumps inside an island but are generally trapped in the island flux tube. For a Hamiltonian with super-diffusive operator and increased stochasticity, enhanced probability for transport is expected at all scales, suggesting the presence of scattering states. Finally, we discuss the implication of this effect to plasma disruptions in fusion devices. This work is supported by DE-SC0023476, DE-SC0023061, DE-SC0024547, DE-FG02-05ER54809, DE-FC02-04ER54698
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