Simulation of Edge Localised Modes using BOUT++

TL;DR

This paper uses the BOUT++ code to simulate edge localized modes (ELMs) in tokamak plasmas, benchmarking ideal MHD models and exploring nonlinear effects, resistivity, and hyper-resistivity at realistic high Lundquist numbers.

Contribution

It demonstrates the capability of BOUT++ to perform nonlinear ELM simulations at high Lundquist numbers and investigates the effects of resistivity and hyper-resistivity on ELM size.

Findings

Good agreement between BOUT++ and ELITE in linear benchmarks.

High Lundquist number simulations show ELM sizes of 5-10% of thermal energy.

Resistivity influences ELM size at low Lundquist numbers, but not at high Lundquist numbers.

Abstract

The BOUT++ code is used to simulate ELMs in a shifted circle equilibrium. Reduced ideal MHD simulations are first benchmarked against the linear ideal MHD code ELITE, showing good agreement. Diamagnetic drift effects are included finding the expected suppression of high toroidal mode number modes. Nonlinear simulations are performed, making the assumption that the anomalous kinematic electron viscosity is comparable to the anomalous electron thermal diffusivity. This allows simulations with realistically high Lundquist numbers S = 1e8, finding ELM sizes of 5-10% of the pedestal stored thermal energy. Scans show a strong dependence of the ELM size resistivity at low Lundquist numbers, with higher resistivity leading to more violent eruptions. At high Lundquist numbers relevant to high-performance discharges, ELM size is independent of resistivity as hyper-resistivity becomes the dominant dissipative effect.