APR domain
The APR method
28.04.2015
The Adaptive-Particle-Refinement (APR) method is applied to the problem of plasma expansion. APR is controlled with the help of a SNR-predictor. SNR-prediction controls APR in a way to keep SNR at a pre-defined level. In order to achieve high SNR multiple quasi-particle species are introduced as is seen from the plot. Also, the number of quasi-particles grows in the course of the plasma expansion:
To keep SNR high the number of different weight species must be limited. The plot below shows how the number of weight species reduced to about only two after the plasma has fully expanded. During the expansion process more than two weight species are required to map the plasma density accurately:
Further complications arise form the fact that the complete phase-space body of the distribution function must be preserved. The specifics of the merging and splitting algorithms makes sure that there are no unacceptable phase-space distortions of the distribution function. Show below is a two-stream scenario at t=0:
Even after 20 merges the original particle distribution is still almost perfect, while the distribution is represented by two orders of magnitude of particles less:
