Impurity collisions

Currently, charged impurities can collide with background plasma ions using two types of the so-called Homma collision operator. To use these type of impurity collisions set use_kin_bg_collisions=.t. and choose kin_bg_coll_type, which is Homma 2020 by defualt.

Homma 2012

Published in [Y. Homma, 2012 JCP], builds on the Monte Carlo Binary Collision Model (BCM) [T. Takizuka, H. Abe, 1977 JCP], and adds the contribution of the thermal force by choosing a background plasma ion velocity from a distorted Maxwell distribution under the temperature gradient. To use this operator, set kin_bg_coll_type=Homma2013.

Homma 2020

Improves the previous model by adding a heat-flux limiter, since the Spitzer-Haerm formula used for the sampled heat-flux is known to be overestimated in low collisionality regimes [Y. Homma, 2020 Nucl. Fusion].

To use this operator, set kin_bg_coll_type=Homma2020.

The heat-flux limiter can be adjusted with the homma2020_alpha parameter, default and recommended value is 1.5 [Fundamenski 2005].