Effects of neoclassical tearing modes and toroidal field ripple on lost alpha power in the SPARC tokamak
Plasma Physics and Controlled Fusion(2022)
Abstract
Abstract Using the SPIRAL Monte Carlo, full particle-orbit simulation code [Kramer PPCF 2013], we investigate the effects of neoclassical tearing modes (NTMs) and toroidal field (TF) ripple on alpha power losses in the SPARC primary reference discharge [Creely JPP 2020, Rodriguez-Fernandez JPP 2020]. Model perturbations for TF ripple and the m/n = 2/1 and 3/2 NTMs with widths selected based on an H-mode thermal quench upper-bound are added to a simulated SPARC magnetic equilibrium through which marker particles are tracked. The 3/2 and 2/1 NTMs are located at ρpol ∽ 0.76 and ρpol ∽ 0.86 respectively, well positioned to increase alpha particle transport into and within an outer lossy region of the plasma beyond ρpol ∽ 0.8 where over 95% of lost alpha particles are born[Scott JPP 2020]. Total alpha power losses are shown to increase modestly from 1.73% lost at a minimum to 2.34% lost at a maximum, and alpha particle surface power densities form localized hotspots on the first-wall near the low-field side midplane due to NTMs and TF ripple. We establish an upper-bound for first-wall alpha surface power densities on a toroidally symmetric wall simulating a locked 2/1 mode scenario and motivate the consideration of NTMs in the design of three dimensional limiter surfaces for SPARC.
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Key words
fusion,fast-ion,SPARC,toroidal field ripple,neoclassical tearing modes,alpha power losses,synergy
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