Energetic particle optimization of quasi-axisymmetric stellarator equilibria

Journal Article · Mon Dec 12 00:00:00 EST 2022 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/aca4e3· OSTI ID:1903396

LeViness, Alexandra ; Schmitt, John C. ; Lazerson, Samuel A. ; Bader, Aaron ; Faber, Benjamin J. ; Hammond, Kenneth C. ; Gates, David A.

Abstract 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 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 QA while minimizing the analytical quantity ${\mathrm{\Gamma }}_{\mathrm{C}}$ , 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 ${\mathrm{\Gamma }}_{\mathrm{C}}$ . The relationship between energetic particle losses and metrics such as QA error ( $E_{\mathrm{q}\mathrm{a}}$ ) and ${\mathrm{\Gamma }}_{\mathrm{C}}$ in this set of equilibria were examined via statistical methods and a nearly linear relationship between volume-averaged ${\mathrm{\Gamma }}_{\mathrm{C}}$ and prompt particle losses was found.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1903396
• Alternate ID(s): OSTI ID: 1899395; OSTI ID: 1905774
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Vol. 63 Journal Issue: 1; ISSN 0029-5515
• Publisher: IOP Publishing
• Country of Publication: IAEA
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
fusion
stellarator
fast ions