This was part of Computational Challenges and Optimization in Kinetic Plasma Physics

Modeling and optimization of Alfvenic instabilities in 3D magnetic fields

Elizabeth Paul, Columbia University

Monday, February 19, 2024


One of the primary requirements of a fusion power plant is the sufficient confinement of the energetic fusion products. Recently, “precisely quasisymmetric” configurations have been obtained through numerical optimization, demonstrating excellent confinement of the guiding center trajectories of fusion-born alpha particles. There is, however, the potential for enhanced alpha losses due to resonant wave-particle interactions. Modeling the dynamics of energetic particles (EPs) presents challenges due to the multi-scale nature of the problem, coupling the shear Alfven waves of the background plasma with drive due to the energetic particle distribution function. Additional physics is introduced in moving from axisymmetric to 3D fields, as complex orbit types and continuum structures arise. We present pathways to model and optimize the alpha transport driven by Alfvenic instabilities in stellarators. Analysis of EP resonances and their impact on saturation mechanisms indicate key departures from the AE-driven transport in tokamaks, such as the avoidance of phase-space island overlap in quasihelical configurations. Taking inspiration from the condensed matter community, we apply spectral density methods to analyze the shear Alfven continuum gap structure and determine the geometric dependence of gap widths.