Plasma-Wall-Interaction Diagnostics for Steady-State Fusion Plasmas

• Applicants: Dr. Sebastijan Brezinsek; Professor Dr. Georg Pretzler
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410415657

Plasma-Wall Interactions (PWI) in fusion devices, especially for future reactors with high performance and steady-state plasma operations such as ITER and CFETR, will determine the life time of Plasma-Facing Components (PFCs), impact the performance of plasmas, and govern the tritium cycle by retention. Therefore, diagnosis and understanding of the PWI processes such as material erosion, transport, and deposition as well as fuel retention by implantation and co-deposition, is crucial in order to control these processes for a safe operation of a reactor at high availability. In order to predict from the PWI in present day devices such as the EAST tokamak (Hefei, China) and the W7-X stellarator (Greifswald, Germany) to future devices numerical simulations are mandatory. Measurements in present-day experiments must be used to verify the codes and the underlying physics of PWI in order to gain confidence in the predictions. Moreover, optimized or novel diagnostics are required to be applicable for in-situ PWI analysis in long-pulse devices to permit access to crucial quantities like the fuel inventory for safety reasons.The present proposal covers the development of in-situ diagnostics systems such as Quartz-Micro Balances (QMBs) and laser-based methods inducing particle ablation (LIBS, LIAS) and testing in laboratory set-ups in China and Germany (ASIPP/Hefei, DUT/Dalian, FZJ/Jülich and HHU/Düsseldorf). QMBs measure in-situ local erosion and deposition by recording the change in the mass-sensitive resonance frequency of the quartz crystal which acts as detector. Optimization concerning thermal stability, sensitivity and calibration is required. Laser-Induced Ablation/Breakdown spectroscopy (LIAS/LIBS) can be performed in-situ and at long detection distance to monitor the hydrogen retention and impurities deposition compositions on the first wall during and between discharges. Optimization concerning the laser-material interaction time, the laser-plasma production process, and calibration is required; all must be accompanied by modelling. Optimized systems will then be integrated in the suite of diagnostics in the metallic long-pulse device EAST, such as the midplane manipulator (MAPES) and visible spectroscopic systems, and dedicated PWI experiments will be carried in the framework of this proposal. A major emphasis will be in the characterization of tungsten (W) PFCs as present in the upper divertor , where spectroscopy combined with LASER-applications and QMBs will be used to determine the major PWI processes covering W, D and seeding gases. Numerical simulations of the plasma edge with the 2D plasma fluid code SOLPS-ITER and the PWI with the 3D Monte-Carlo code ERO are performed jointly and will be applied to support the interpretation of experimental findings. Finally, the optimized and qualified diagnostics and a subset of codes will be adapted in future to the conditions of W7-X, currently operationg with graphite, and the metallic CFETR.

• DFG Programme: Research Grants
• International Connection: China
• Major Instrumentation: Fast intensified CCD camera (ICCD)
• Instrumentation Group: 5430 Hochgeschwindigkeits-Kameras (ab 100 Bilder/Sek)
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partners: Professor Junling Chen; Professor Hongbin Ding