Abstact:
Nuclear fusion holds promise as a clean and renewable energy source. Despite its conceptual origins in the early 20th century, practical implementation remains a formidable challenge.

Fusion reactors, such as the Tokamak—introduced in the 1950s by Soviet scientists—and the Stellarator—developed around the same time in the United States—are among the most advanced devices designed to achieve fusion. These intricate machines are still under active development, and computer simulation plays a crucial role in, for instance, validating physical theories and testing new device components, or even designing the next-generation reactor.

One simulation tool is the code suit EIRENE, which models neutral particles in the edge regions of fusion devices using the Boltzmann-BGK equation. This equation is solved via the Monte Carlo method, which typically delivers acceptable convergence for smaller devices. However, as devices grow larger, computational costs escalate. Fortunately, in large devices, frequent particle collisions allow the Boltzmann-BGK equation to be approximated by a fluid model, providing significant computational speed-ups.

In this talk, designed for the general audience, I will first introduce the physical background and then the Monte Carlo method. Afterward, I will explain the derivation of the fluid model from the Boltzmann-BGK equation and describe corresponding hybrid algorithms.