Tuesday, June 25, 2013

1306.5700 (Ryan T. Wollaeger et al.)

Radiation Transport for Explosive Outflows: A Multigroup Hybrid Monte Carlo Method    [PDF]

Ryan T. Wollaeger, Daniel R. van Rossum, Carlo Graziani, Sean M. Couch, George C. Jordan IV, Donald Q. Lamb, Gregory A. Moses
We explore the application of Implicit Monte Carlo (IMC) and Discrete Diffusion Monte Carlo (DDMC) to radiation transport in strong fluid outflows with structured opacity. The IMC method of Fleck & Cummings is a stochastic computational technique for nonlinear radiation transport. IMC is partially implicit in time and may suffer in efficiency when tracking Monte Carlo particles through optically thick materials. The DDMC method of Densmore accelerates an IMC computation where the domain is diffusive. Recently, Abdikamalov extended IMC and DDMC to multigroup, velocity-dependent neutrino transport with the intent of modeling neutrino dynamics in core-collapse supernovae. Densmore has also formulated a multifrequency extension to the originally grey DDMC method. In this article we rigorously formulate IMC and DDMC over a high-velocity Lagrangian grid for possible application to photon transport in the post-explosion phase of Type Ia supernovae. The method described is suitable for a large variety of non-monotonic opacity distributions and may be applied to first-order relativistic radiation transport in simple velocity fields and geometries. In addition to describing the method, we test the code, called SuperNu, using an analytic solution that assumes static material, as well as with a manufactured solution for moving material with simple yet highly structured opacities. Finally, we demonstrate with a simple source and 10 group, logarithmic wavelength grid that increasing the disparity between opacity magnitudes of adjacent groups further improves the performance of IMC-DDMC relative to pure IMC.
View original: http://arxiv.org/abs/1306.5700

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