Collisional gyrokinetic full‐f particle‐in‐cell simulations on open field lines with PICLS

Mathias Boesl,Stephan Brunner,David Coster,Frank Jenko,Andreas Bergmann,Alberto Bottino

doi:10.1002/ctpp.201900117

Abstract

AbstractApplying gyrokinetic simulations in theoretical turbulence and transport studies for the plasma edge and scrape‐off layer (SOL) presents significant challenges. To particularly account for steep density and temperature gradients in the SOL, the “full‐f” code PICLS was developed. PICLS is a gyrokinetic particle‐in‐cell (PIC) code, is based on an electrostatic model with a linearized field equation, and uses kinetic electrons. In previously published results, we applied PICLS to the well‐studied 1D parallel transport problem during an edge‐localized mode (ELM) in the SOL without collisions. As an extension to this collision‐less case and in preparation for 3D simulations, in this work, a collisional model will be introduced. The implemented Lenard–Bernstein collision operator and its Langevin discretization will be shown. Conservation properties of the collision operator, as well as a comparison of the collisional and non‐collisional case, will be discussed.

Highlights

In the closed field line region of the plasma core, gyrokinetics has become the workhorse for turbulence simulations in the last decades, but their extension towards the plasma edge and scrape-off layer (SOL) demonstrates additional challenges
Simulation results for collision operator testing and the 1D2V collisional heat pulse problem are shown in Sections 4 and 5
By choosing an arbitrary initial velocity distribution, which has to relax according to Equation (23), we can construct the first test case for the implemented collision operator

Summary

INTRODUCTION

In the closed field line region of the plasma core, gyrokinetics has become the workhorse for turbulence simulations in the last decades, but their extension towards the plasma edge and scrape-off layer (SOL) demonstrates additional challenges. In a previous work,[1] we investigated the well-studied problem of parallel energy and particle transport caused by a transient Type I edge-localized mode (ELM) in the SOL. In this study, we implement a Lenard–Bernstein (LB) collision operator in our newly developed PICLS code, which is designed to perform gyrokinetic SOL simulations.[1] For the applied PIC model, the operator is discretized via a Langevin approach.[7] We will show that the implemented LB collision operator conserves particle number, parallel momentum, and energy and relaxes towards a Maxwellian. Simulation results for collision operator testing and the 1D2V collisional heat pulse problem are shown in Sections 4 and 5.

PHYSICAL MODEL

LB COLLISION OPERATOR

SIMULATION RESULTS

CONCLUSIONS