Effect of symmetry breaking on neoclassical flow damping in the Columbia Stellarator eXperiment

A primary goal of the Columbia Stellarator eXperiment (CSX) is to empirically validate predicted properties of quasiaxisymmetric (QA) stellarators. Quasisymmetric stellarators are generally expected to exhibit reduced flow damping along the direction of symmetry as well as reduced neoclassical heat flux relative to unoptimized stellarators. In this work, we assess the toroidal flow damping time scale in CSX by performing neoclassical calculations using the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver (SFINCS) (Landreman et al., 2014). Varying the degree of symmetry breaking in the magnetic field, we predict the flow damping time scale for several plausible experimental configurations and examine its dependence on quasisymmetry error. The dependence of the plasma flow direction on the quasisymmetry error is also reassessed. We additionally confirm that neoclassical heat flux decreases with quasisymmetry error and compare the expected neoclassical and turbulent (gyro-Bohm) heat fluxes in CSX to those of its non-quasisymmetric predecessor, the Columbia Non-neutral Torus (CNT).