Comparison of four parallel algorithms for domain decomposed implicit Monte Carlo

We consider four asynchronous parallel algorithms for Implicit Monte Carlo (IMC) thermal radiation transport on spatially decomposed meshes. Two of the algorithms are from the production codes KULL from Lawrence Livermore National Laboratory and Milagro from Los Alamos National Laboratory. Improved versions of each of the existing algorithms are also presented. All algorithms were analyzed in an implementation of the KULL IMC package in ALEGRA, a Sandia National Laboratory high energy density physics code. The improved Milagro algorithm performed the best by scaling almost linearly out to 244 processors for well load balanced problems.