Comparison of bootstrap current calculation in helical plasmas among different types of approximations in drift-kinetic equation

Huang, B.*; Satake, Shinsuke*; Kanno, Ryutaro*; Matsuoka, Seikichi 

The bootstrap current, or the parallel flow in a toroidal plasma is described by the neoclassical transport theory. In recent studies, it was pointed out that numerical models of the radially-local neoclassical transport, in which the radial drift of particles is entirely neglected, can be classified according to approximations used in the models. In this work, we perform a series of benchmarks of the parallel flow for the LHD, HSX, and W7-X by using three types of the local neoclassical transport simulations models. It is shown that the magnetic drift tangential to a flux surface significantly changes the parallel flow when the radial electric field is weak in a low-collisional LHD plasma. We also find that the effect of the tangential drift becomes small in other magnetic configurations of HSX and W7-X.