Description
Neoclassical transport coefficients are essential for understanding particle and heat transport in tokamak plasmas, particularly in the presence of 3D magnetic perturbations. Traditionally, these coefficients have been calculated by directly solving the drift-kinetic equation [1,2]. While Monte-Carlo methods offer a more direct approach, they have traditionally been limited by computational constraints due to the inherent statistical noise which requires a large number of particles for convergence. We present a GPU-accelerated implementation of the VENUS-LEVIS [3] particle transport code that overcomes this limitation by enabling massively parallel simulations of millions of particles.
The new implementation of VENUS-LEVIS is architecture independent and can run on a laptop CPU or a large-scale GPU cluster. The high-performance code allows for full-f and delta-f Monte Carlo calculations of neoclassical coefficients [4]. The method naturally captures the effects of different collisionality regimes from banana to Pfirsch-Schlüter, and the influence of non-axisymmetric perturbations such as internal kinks or external MHD modes. This method is crucial for extending the transport code beyond ideal MHD, such as Neoclassical Tearing Modes.
This computational advantage has an immediate application for the study of heavy impurity transport, crucial for ITER [5] and future reactors employing tungsten plasma-facing components. For accurate simulations, the interaction of tungsten with the background plasma needs to be considered. A custom Coulomb collision operator [6] is used that relies on neoclassical transport coefficients of both impurities and main light ions, which can be calculated with VENUS-GPU.
[1] S. P. Hirshman et al., Physics of Fluids, 29, 2951–2959. 1986
[2] M. Landreman et al., Physics of Plasmas. 21, p. 042503. Apr. 2014
[3] D. Pfefferlé et al., Comput. Phys. Commun. 185, pp. 3127–3140. 2014
[4] J. Koerfer et al., Theory of Fusion Plasmas / Joint Varenna - Lausanne International Workshop. Sep. 2024 (poster)
[5] A Loarte et al, Plasma Phys. Control. Fusion. 67 065023, Jun. 2025
[6] E Lascas Neto et al., Plasma Physics and Controlled Fusion. 64, p. 014002. Nov. 2021