Abstract
Particle simulations with Monte Carlo collision models have been widely used to efficiently solve Coulomb collisions in plasma systems. A binary collision Monte Carlo model which has been proposed previously provides more accurate results than the commonly used Nanbu’s model for electron-ion temperature relaxation. In the present work, this binary model is generalized to simulate multicomponent plasmas, and its results still show higher accuracy than Nanbu’s model when compared to the baseline results obtained from Particle-Particle simulations. In addition, the binary model is improved to eliminate the time step length limitation occurred in the previous algorithm.
Highlights
When different plasma components have distinct temperatures, those that have higher temperatures transfer energy to those with lower temperatures mainly through Coulomb collisions, until all the components reach the same equilibrium temperature
Since the fusion burn rate is extremely sensitive to the ion temperature, knowing the precise temperature relaxation is crucial
There are three basic types of particle simulations:[3] the Particle-Particle (PP) model,[4,5,6] which has the highest accuracy but the largest computational cost; the Particle-Mesh model,[2,7,8] which reduces the computational cost at the expense of accuracy; and the Particle-Particle-Particle-Mesh model,[1] which combines the two, but its mesh size must be determined carefully.[3]
Summary
When different plasma components have distinct temperatures, those that have higher temperatures transfer energy to those with lower temperatures mainly through Coulomb collisions, until all the components reach the same equilibrium temperature. Two general and widely used Monte Carlo collision models are Takizuka and Abe’s9 and Nanbu’s.10 These two models have been shown to produce similar stochastic errors, but Nanbu’s gives smaller time step errors.[11] For the specific temperature relaxation problems, a previous work[4] shows that the simulation results of Nanbu’s model does not match well with those of the PP model, but a new binary collision Monte Carlo model, proposed in that work, gives a good match. This binary model is generalized to solve for multicomponent plasmas, and improved to eliminate the limitation of the time step length. To show this binary model is still more accurate than Nanbu’s model, the PP model is used again as a baseline to compare its results with those of the binary model and Nanbu’s model. J=1 j=1 where NS denotes the number of species and nj denotes the number density of the jth species
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