VETTAM: a scheme for radiation hydrodynamics with adaptive mesh refinement using the variable Eddington tensor method

We present Variable Eddington Tensor-closed Transport on Adaptive Meshes (\texttt{VETTAM}), a new algorithm to solve the equations of radiation hydrodynamics (RHD) with support for adaptive mesh refinement (AMR) in frequency-integrated, two-moment formulation. The method is based non-local Tensor (VET) closure computed hybrid characteristics scheme ray tracing. use Godunov hyperbolic transport an implicit backwards-Euler temporal update avoid explicit timestep constraint imposed by light-crossing time, and fixed-point Picard iteration handle nonlinear gas-radiation exchange term, two stages jointly iterated convergence. also develop modified wave-speed correction AMR, which we find be crucial obtaining accurate results diffusion regime. demonstrate robustness our suite pure RHD tests, show that it successfully captures streaming, static diffusion, dynamic regimes spatial transitions between them, casts sharp shadows, yields rates momentum energy gas. A comparison different closures moment equations, approximation (0th-moment closure) $M_1$ (1st-moment closure), demonstrates advantages VET (2nd-moment over simpler schemes. \texttt{VETTAM} has been coupled AMR \texttt{FLASH} (magneto-)hydrodynamics code summarize reporting performance features bottlenecks implementation.