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arXiv · 2509.03942

Fluid boundary conditions in kinetic-diffusion Monte Carlo

Thijs Steel·Vince Maes·Giovanni Samaey
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Abstract

The Kinetic-Diffusion Monte Carlo (KDMC) method is a powerful tool for simulating neutral particles in fusion reactors. It is a hybrid fluid-kinetic method that is significantly faster than pure kinetic methods at the cost of a small bias due to fluid approximations. Unfortunately, when simulating particles close to a boundary, it needs to switch to a purely kinetic method, which is significantly slower. In this paper, we will extend the method so that it can accurately take boundary conditions into account without switching to a purely kinetic method. Experiments show that this extension can lead to a speedup of up to 500 times compared to a KDMC method that switches to a purely kinetic method, while not sacrificing too much accuracy.

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Thijs Steel, Vince Maes, Giovanni Samaey. 2025-09-04. Fluid boundary conditions in kinetic-diffusion Monte Carlo. https://arxiv.org/abs/2509.03942

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