Application of Lorentz collision operator in the gyrokinetic code NLT

In this work, a Lorentz collision operator is implemented in the NLT code. This module uses the 4-th order accurate finite-difference scheme and a correction algorithm, which suppresses the spurious diffusion and ensures the numerical conservation properties, respectively. The neoclassical parallel electrical conductivity and the neoclassical ion thermal conductivity cases are tested, and the simulation results agree well with the theory. Finally, the formation of the parallel return flow through the ambipolar radial electric field and the collisional relaxation to the rigid-body toroidal rotation are further investigated.