Energetic particle optimization of quasi-axisymmetric stellarator equilibria

LeViness, Alexandra; Schmitt, John; Lazerson, Samuel; Bader, Aaron; Faber, Benjamin; Hammond, Kenneth; Gates, David
Issue date: 2022
Cite as:
LeViness, Alexandra, Schmitt, John, Lazerson, Samuel, Bader, Aaron, Faber, Benjamin, Hammond, Kenneth, & Gates, David. (2022). Energetic particle optimization of quasi-axisymmetric stellarator equilibria [Data set]. Princeton Plasma Physics Laboratory, Princeton University.
  author      = {LeViness, Alexandra and
                Schmitt, John and
                Lazerson, Samuel and
                Bader, Aaron and
                Faber, Benjamin and
                Hammond, Kenneth and
                Gates, David},
  title       = {{Energetic particle optimization of quasi
                -axisymmetric stellarator equilibria}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2022

An important goal of stellarator optimization is to achieve good confinement of energetic particles such as, in the case of a reactor, alphas created by Deuterium-Tritium (D-T) fusion. In this work, a fixed-boundary stellarator equilibrium was re-optimized for energetic particle confinement via a two-step process: first, by minimizing deviations from quasi-axisymmetry (QA) on a single flux surface near the mid-radius, and secondly by maintaining this improved quasi-axisymmetry while minimizing the analytical quantity ΓC , which represents the angle between magnetic flux surfaces and contours of J||, the second adiabatic invariant. This was performed multiple times, resulting in a group of equilibria with significantly reduced energetic particle losses, as evaluated by Monte Carlo simulations of alpha particles in scaled-up versions of the equilibria. This is the first time that energetic particle losses in a QA stellarator have successfully been reduced by optimizing ΓC . The relationship between energetic particle losses and metrics such as QA error (Eqa) and ΓC in this set of equilibria were examined via statistical methods and a nearly linear relationship between volume-averaged ΓC and prompt particle losses was found.

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