Numerical modeling of the thermal force in a plasma for test-ion transport simulation based on a Monte Carlo Binary Collision Model (II) - Thermal forces due to temperature gradients parallel and perpendicular to the magnetic field

We have developed a numerical model of the thermal force for test-ion transport simulation in a magnetized background plasma, based on the Monte Carlo Binary Collision Model (BCM) [T. Takizuka, H. Abe, J. Comput. Phys. 25 (1977) 205]. The model is basically the same as presented in our previous paper [Y. Homma, A. Hatayama, J. Comput. Phys. 231 (2012) 3211-3227] for the case without magnetic field, but in the present paper, a more extended form of a distorted Maxwellian distribution is employed for the velocity distribution of background plasma ions to simulate the thermal force caused by parallel and perpendicular (with respect to the direction of magnetic field) temperature gradients. The model consists mainly of two steps: (i) choosing a background plasma ion velocity from a distorted Maxwellian distribution, and (ii) calculating a Coulomb collision between a test particle and the above chosen ion by using the BCM. In addition, equations of motion for charged test particle in the magnetic field are calculated by Buneman-Boris Algorithm.A series of test simulations has been done in a simple geometry with different temperature gradients and different strengths of magnetic field. Numerical results of the thermal force due to parallel and perpendicular temperature gradients agree well with the theoretical prediction for all test cases. Especially, it has been confirmed that the model reproduces the temperature screening effect of test particles (i.e. guiding center drift of test particle caused by the thermal force of perpendicular temperature gradient).