# A Multigroup Moment-Accelerated Deterministic Particle Solver for Time-dependent Thermal Radiative Transfer Problems

## TL;DR

This paper introduces a novel Lagrangian particle-based solver for time-dependent thermal radiative transfer that combines advantages of particle and deterministic methods, enabling accurate results with large time steps.

## Contribution

It presents a new characteristic-based transport algorithm within a moment-accelerated framework, improving efficiency and robustness for TRT simulations.

## Key findings

- Achieves accurate results with fewer particles and larger time steps.
- Combines benefits of particle and grid-based methods.
- Handles stiff absorption and reemission self-consistently.

## Abstract

We propose an efficient, robust, Lagrangian (characteristic-based) transport solver for the time-dependent thermal radiative Transfer (TRT) applications within the context of a moment-accelerated (High-Order/Low-Order, HOLO) algorithm. This novel transport algorithm inherits the best features of both particle methods (e.g., time accuracy, phase-space adaptivity, positivity) and deterministic, grid-based methods (e.g., no stochastic noise). Particles are evolved by the method of characteristics, with a time-dependent weight that accounts for stiff absorption and reemission process self-consistently. As a result, this approach is able to obtain accurate results while employing large time steps and a moderate number of particles (compared to Implicit Monte Carlo).