Improved Conservative Scheme for Lenard‐Bernstein Collisions in Gyrokinetic Turbulence Simulations

Abstract

Turbulence in the edge and scrape‐off layer regions plays a critical role for the performance of future magnetic confinement fusion power plants. Gyrokinetic simulations allow studying this regime with high fidelity. A key aspect in these regions is the high concentration of impurities, which can radiate energy, leading to significant losses. Due to large mass and high charge state, impurities are highly collisional, making them difficult to model accurately. This work presents discretization and algorithmic improvements for Lenard‐Bernstein collisions in gyrokinetic simulations based on previous conservative finite‐volume scheme. The new discretization improves numerical consistency by eliminating conservation errors, which were previously circumvented through the use of free parameters. While small boundary corrections remain necessary, we show that numerical conservation can be improved through careful stencil design, reducing reliance on free parameters. Its implementation is verified through conservation and relaxation tests. The algorithmic improvements focus on computational performance, achieving compute and communication performance gains in a scaled‐down TCV‐X21 benchmark. It also scales as with the number of species , significantly improving upon the previous naive implementation.