Magneto-Hydrodynamic Simulations of Pedestal Instabilities for Tokamak Plasmas with Different Ion Masses

TL;DR

This study uses MHD simulations to analyze how different ion masses affect pedestal instabilities in tokamak plasmas, revealing small variations primarily due to MHD momentum effects and highlighting the need to include turbulence for accurate modeling.

Contribution

It demonstrates the impact of ion mass variations on pedestal stability using extended MHD simulations and compares results with experimental data, emphasizing the importance of turbulence modeling.

Findings

Small variations in stability with ion mass changes, mainly due to MHD momentum.

Simulated ELM crashes show differences in heat and particle losses.

Experimental differences not fully reproduced, indicating missing turbulence effects.

Abstract

In this bachelor's thesis, isotope effects for pedestal instabilities have been studied based on an ASDEX Upgrade H-Mode scenario. This was done using the JOREK code for extended MHD simulations, including the ion diamagnetic drift and the establishment of ExB flows. Simulations with single toroidal harmonics were performed for multiple times during the build-up of the pedestal, to assess the evolution of the linear stability of modes occurring near the edge. When changing the average ion masses from 2.0 to 2.5 and 3.0, the variations were small, and MHD's momentum equation was shown to be the major cause for them. As a second step, simulations with multiple toroidal harmonics were performed to simulate an Edge Localized Mode (ELM) crash, again comparing between the average ion masses of 2.0, 2.5, and 3.0. The resulting variations of heat and particle losses were compared to JET results. The experimental differences between ion masses could not be reproduced. Together with the fact that the simulations' pedestal for an average ion mass of 2.5 and 3.0 was not matched to the experiment, this indicates that other effects, such as small-scale turbulences, must be included - for example, by adapting the simulations' transport coefficients - to explain the experimental differences.