# Enabling Radiative Transfer on AMR grids in CRASH

## TL;DR

CRASH-AMR enhances radiative transfer simulations by enabling adaptive mesh refinement, improving accuracy in high-density regions without increasing computational cost, validated through tests with ionised gas regions.

## Contribution

The paper introduces CRASH-AMR, a novel version of the CRASH code that incorporates adaptive mesh refinement for more precise radiative transfer modeling.

## Key findings

- CRASH-AMR achieves higher resolution in ionised regions.
- The code maintains accuracy comparable to previous versions.
- Simulation speed improves by up to 60% with AMR.

## Abstract

We introduce CRASH-AMR, a new version of the cosmological Radiative Transfer (RT) code CRASH, enabled to use refined grids. This new feature allows us to attain higher resolution in our RT simulations and thus to describe more accurately ionisation and temperature patterns in high density regions. We have tested CRASH-AMR by simulating the evolution of an ionised region produced by a single source embedded in gas at constant density, as well as by a more realistic configuration of multiple sources in an inhomogeneous density field. While we find an excellent agreement with the previous version of CRASH when the AMR feature is disabled, showing that no numerical artifact has been introduced in CRASH-AMR, when additional refinement levels are used the code can simulate more accurately the physics of ionised gas in high density regions. This result has been attained at no computational loss, as RT simulations on AMR grids with maximum resolution equivalent to that of a uniform cartesian grid can be run with a gain of up to 60% in computational time.