Gyrokinetic calculations of the neoclassical radial electric field in stellarator plasmas

A novel method to calculate the neoclassical radial electric field in stellarator plasmas is described. The method, which does not have the inconvenience of large statistical fluctuations (noise) of the standard Monte Carlo technique, is based on the variation of the combined parallel and perpendicular pressures on a magnetic surface. Using a three-dimensional gyro-kinetic δf code, the calculation of the radial electric field (E r ) in the National Compact Stellarator Experiment [G. H. Neilson et al., Phys. Plasmas 7, 1911 (2000)] has been carried out. It is shown that a direct evaluation of E r based on a direct calculation of the radial particle flux is not tractable due to the considerable noise.