3D simulation of impurity transport in a fusion edge plasma using a massively parallel Monte-Carlo code

Abstract

Thermonuclear fusion of deuterium (D) and tritium (T) has the potential to be an efficient, sustainable and safe source of energy. The international tokamak fusion experiment ITER (Latin: "the way"), which is scheduled to start operation in 2027, is a key project for the realization of this technology. Reliable predictions on the plasma-wall interaction (PWI) are critical to the success of ITER and further upcoming fusion reactors, since these will significantly impact their efficiency and lifespan. An important PWI process is the erosion of the reactor wall. It determines the lifetime of wall components and is also a source of impurities in the plasma, namely beryllium (Be) and tungsten (W) in the case of the metallic ITER first wall. Codeposition and retention of radioactive T with eroded Be is a significant issue for ITER, since its T wall inventory has an administrative limit of 700 g for safety and fuel cycle reasons. The penetration of impurities (in particular of W, which can reach a high degree of ionization) into the plasma core leads to its cooling due to radiative energy losses, which has a deteriorating impact on confinement and stability. The three-dimensional Monte Carlo (MC) code ERO is an established tool for the investigation and prediction of PWI and plasma impurity transport in fusion experiments. However, due to technical aspects, such as most importantly the limited code performance, ERO was used so far for examining small simulation volumes (under $\sim$ 1m$^{3}$), which is a small fraction of the ITER plasma volume($\sim$ 800m$^{3}$). Thus, addressing the interdependent problem of impurity transport and PWI in the tokamak has demanded additional assumptions (for example, on the impurity content in the plasma). Moreover, the possibilities of code validation based on measurements in fusion experiments were limited, since only local diagnostics could be used. In the framework of this thesis, the ERO code has been redeveloped from scratch to remove these restrictions. The new code ERO2.0 implements algorithms that allow to study large and complexly shaped wall components in a simulation volume of the ITER plasma vessel size. The resulting increased complexity of the simulation requires to enhance the code performance by orders of magnitude. [...