Simulation and experiment investigating neoclassical effects of impurities on bootstrap current in HSX

Impurity accumulation is a major concern for stellarators, and HSX provides a chance to understand impurity dynamics in a low-shear quasi-symmetric device. Calculations with SFINCS have shown that small changes in $Z_{eff}$ impact the bootstrap current in W7-X.\footnote{A. Moll\'en et al, J. Phys.: Conf. Ser., 561, 012012, 2014.} The PENTA and SFINCS codes are in use at HSX and can solve the drift-kinetic equation with multiple plasma species. PENTA is a momentum conserving extension of the DKES code, which calculates the monoenergetic transport matrix on a flux surface using a moments approach. SFINCS is a four dimensional drift-kinetic continuum code. We compare calculations with PENTA and SFINCS for HSX plasmas with varying impurities, focusing on effects on the bootstrap current. Experimental measurements of the bootstrap current using a Rogowski coil are compared to simulation results where possible.