Speaker
Michael Rack
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1014.pdf
Neutral sampling vs. particle-identity conservation in a coupled
fluid-kinetic Monte-Carlo code environment
M. Rack1 , D. Reiter1 , Y. Feng2 and H. Frerichs3
1 Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik,
Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
2 Max-Planck-Institut für Plasmaphysik, 17491 Greifswald / 85748 Garching, Germany
3 Department of Engineering Physics, University of Wisconsin–Madison, Madison, Wisconsin
53706, USA
Since early 1990s the magnetic confined fusion community utilises coupled code environ-
ments for a self-consistent description of plasma flow and neutral gas transport in the edge
region of toroidal fusion devices [1]. Usually, the plasma is treated with a fluid approach and
the neutral gas transport requires a kinetic consideration. In two dimensions the plasma solu-
tion is often calculated with implicit discretization schemes (cf. B2, EDGE2D, SOLEDGE-2D),
whereas the neutral gas distribution is acquired via a Monte-Carlo technique to solve the lin-
earized Boltzmann equation (cf. EIRENE, Degas 2). Consequently, the origin of neutrals is
sampled from a distribution which adds numerical noise to the simulation result. Especially in
large divertor tokamak geometries, noise effects are difficult to separate from physically driven
instabilities [2]. Therefore, various noise cancellation techniques such as “correlated sampling”
have been implemented to overcome this problem [3].
In contrast, plasma solutions for three-dimensional geometries are usually calculated based
on a diffusion-advection Monte-Carlo technique that solves the fluid equation after transforma-
tion to Fokker-Planck form (cf. EMC3 [4]). This can be understood as a particle-like treatment
of fluid parcels in the transport code. In other words, the particle-identity can be conserved in the
interface between the fluid and kinetic code. In the code package used here (EMC3-EIRENE),
neutral sampling is the default option; however, particle-identity conservation may bring an ad-
vantage to the numerical stability. Internally, EMC3 already uses a very strict particle-identity
conserving scheme, which is one reason for the strength of EMC3 compared to other approaches
for three-dimensional fluid solvers. In this contribution, we describe the currently developed
particle-identity conserving interface and compare it to the sampling approach.
References
[1] D. Reiter. Journal of Nuclear Materials, 196-198, 80 (1992).
[2] V. Kotov. Physics of Plasmas, 24 (4), 042511 (2017).
[3] D. Stotler et al. Contributions to Plasma Physics, 40 (3-4), 221 (2000).
[4] Y. Feng et al. Journal of Nuclear Materials, 266-269, 812 (1999).
