Computational plasma physics Low Temperature

Mission statement

The general aim of the CPP-LT group is the development and application of advanced numerical and theoretical models to describe the physics of low temperature plasma and plasma surface interaction.

Long term aims

The research of the CPP-LT group is done within the framework of Fusion Energy. The research line of the institute on Plasma Surface Interactions requires support from simulations and analysis with sophisticated numerical and theoretical models. The aim of the CPP-LT group is to develop new and modify existing models for this purpose. Models on the other hand benefit from validation against experimental data. This holds especially for the suite of numerical tools needed to support ITER and the design of future reactors like DEMO. Relevant models, validated against experimental data from Magnum- and Pilot-psi, will be applied to the plasma in the ITER divertor and will be made available to the EFDA task force for Integrated Tokamak Modeling.

A number of simulation tools has been or will be acquired and developed to study all aspects of plasma surface interaction in Magnum- and Pilot-psiPSI. These tools address the physics of the plasma beam and its recycling at the target, the details of the plasma-surface interaction, and the migration of released target material.
The framework for collaboration within EURATOM is provided by the task forces for Integrated Tokamak Modeling (ITM) and Plasma Wall Interaction (PWI). The scientific program will provide ample possibilities for the education of PhD students and trainees.

Staff

Current research and highlights

Simulation of the Magnum-PSI and Pilot-PSI plasma beam and its interaction with the target is based on the B2.5 - Eunomia package. (developed by Rob Wieggers). This package consists of B2.5 (a fluid description of the magnetized plasma) coupled to Eunomia, a Monte Carlo description of the neutral species. Important features of Eunomia are a high degree of parallelism and good statistics, both near the axis if the beam and in the space between the beam and the vessel wall. Improvement of the statistics is accomplished by adapting the weight of the particles to the size of the computational cells.

Validation against experimental data is mainly based on Thomson scattering and spectroscopy, especially of the hydrogen Balmer lines. Vibrationally excited molecules were found to have a significant influence on the Balmer emission, making it mandatory to follow excited molecules as separate species with Eunomia.

Eunomia is equipped with a collisional-radiative model that predicts the densities of the atomic excited states. In this model, the generation of excited states via molecular processes (dissociative recombination, dissociative attachment, ion-ion recombination) is included.

Simulation of erosion, transport, and redeposition of wall material is modelled with the ERO code (by Gijs van Swaaij). After being released from the surface, test particles are followed through the plasma beam, where they interact with the plasma species. Processes included are charge exchange followed by dissociative recombination, ionization, and Coulomb interaction.

From the ERO simulations a transport matrix can be constructed that connects the initial position on the target and the position where a particle returns to the target. This approach enables fast studies of the effect of choices for sticking probabilities, etc.

An earlier study was dedicated to the influence of dissociative recombination processes on the generation of the Gerö band emission of the CH radical. Validation against experimentally observed emission from a methane gas puff at the side of the Pilot-PSI beam showed that the recorded dissociative recombination events show a much better match than the electron excitation events.