Calculation Of The Nanbu-Trubnikov Kernel: Implications For Numerical Modeling Of Coulomb Collisions. 2009 SIAM Annual Meeting Denver, CO, United States July 6, 2009 through July 10, 2009

摘要

We investigate the accuracy of and assumptions underlying the numerical binary Monte-Carlo collision operator due to Nanbu. The numerical experiments that resulted in Nanbus parameterized collision kernel are approximate realizations of the Coulomb-Lorentz pitch-angle scattering process, for which an analytical solution is available. It is demonstrated empirically that Nanbus collision operator quite accurately recovers the effects of Coulomb-Lorentz pitchangle collisions, or processes that approximate these even for very large values of the collisional time step. An investigation of the analytical solution shows that Nanbus parameterized kernel is highly accurate for small values of the normalized collision time step, but loses some of its accuracy for larger values of the time step. Finally, a practical collision algorithm is proposed that for small-mass-ratio Coulomb collisions improves on the accuracy of Nanbus algorithm.