Abstract Details
Abstracts
Author: Jessica R.J. Eskew
Requested Type: Poster
Submitted: 2025-03-14 10:45:57
Co-authors: B.R.Andrew, D.M.Orlov, C. Marini, T. Cote, E.G. Kostadinova
Contact Info:
Auburn University
380 Duncan Drive
Auburn, 36849
United States
Abstract Text:
Understanding the mechanisms of energetic electron (EE) generation and transport is crucial to predict and mitigate damage in fusion devices during plasma disruptions. Although EEs are known to form during plasma startup as a result of current ramp-up, additional mechanisms may contribute to their generation later in the discharge. Notably, in stellarators—where large currents are absent—alternative mechanisms for EE acceleration must exist. One proposed mechanism is EE trapping and secondary generation within magnetic islands, where island topology influences confinement and acceleration.
This work investigates the role of magnetic island bifurcation in modifying EE diffusion through the analysis of DIII-D experiments. In these experiments, static islands were grown and manipulated through resonant magnetic perturbations using I-coils. Synchrotron emission measurements were used to confirm that magnetic islands on the q=2 surface can trap EEs with energies $gtrsim$ 10 MeV. However, periodic bursts of X-ray signals observed during island rotation suggest that EEs escape confinement and impact the device walls. These bursts coincide with the periodic bifurcation of the island chain on the q=2 rational surface which leads to a switch between a homoclinic structure dominated by the 2/1 mode and a heteroclinic structure dominated by the 4/2 mode.
Here, we implement a collisional operator into the TRIP3D field-line tracing code to further explore how island topology affects EE diffusion. Simulations with 10,000 electron tracers are used to quantify diffusion characteristics for different island configurations. We analyze stochasticity using displacement histograms, island width calculations, and Chirikov parameters. This work provides a theoretical framework for understanding EE transport in bifurcating magnetic islands, with implications for disruption mitigation and confinement optimization in fusion plasmas.
Characterization: 1.0
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