Scrape-off layer and plasma-wall interaction

Controlling and mitigation the interaction of the thermalised plasma with the surrounding wall is one of the most challenging task in building a fusion power plant. Used materials in fusion experiments include carbon (carbon fibre composites, CFCs) and metals (beryllium, molybdenum, tungsten). The amount of power these materials can absorb before being significantly damaged is limited, typically to 10s of MW/m2, set by their thermo-mechanical properties. Hence, the plasma at the very edge – the scrape-off layer – needs to be sufficiently cooled before meeting the material surface. Concomitantly, impurities produced at the material surfaces due to plasma impact can penetrate the region where the fusion process takes place – the core plasma – and thereby incidentally dilute the fuel and cool the core plasma.

The common theme of the group is the analysis of experimental data and interpretation thereof using existing plasma boundary codes toward understanding power exhaust in tokamaks. The boundary plasma - also known as the scrape-off layer - is immediately outside of the fusing core plasmas. The remaining heat from the core plasma (Megawatts!) is carried to the plasma-surrounding wall via the boundary plasma. Understanding and eventually controlling the processes in the boundary plasma is of critical importance to successfully operating a fusion device.

Simulations of the processes in the scrape-off layer require taking into account an open magnetic field line geometry and a significant neutral and impurity population in the plasmas. Our research focuses on understanding the scrape-off layer utilising several simulation codes developed outside the group and validating their predictions against detailed measurements in JET, ASDEX Upgrade, and other tokamaks.

and are coupled fluid plasma (B2) – Monte Carlo neutrals (Eirene) codes and two of the primary tools used for modelling the scrape-off layer. UEGDE is a fluid plasma, fluid neutral code also to simulate the scrape-off layer in fusion devices. The codes typically take experimental data, such as core power and density as input and predict the scrape-off layer conditions. The Onion Skin-Model is another fluid code to predict the state of the scrape-off layer typically starting from the plasma conditions at the material surfaces.
The impurity code simulates erosion of a material surface due to plasma contact and follows the released impurity particles in a restricted plasma volume close to the surface. Uniquely, subsequent local re-deposition and re-erosion are taken in account. The required plasma parameters can be taken from one of fluid codes.
The impurity Monte-Carlo code simulates impurity transport within the entire scrape-off layer for a given background plasma. The code follows a population of ions or atoms until they are deposited on the walls.
The ion-orbit following ASCOT is also been used to following impurity ions in the scrape-off layer in a realistic 3-D magnetic and wall geometry. Like DIVIMP, the code follows a population of ions until they are deposited on the walls.

Experimental characterisation of divertor plasmas in the JET (UK), ASDEX Upgrade (Germany) and DIII-D (US) ⇒ execution of experiments at these facilities
Simulations of the scrape-off layer plasma in JET, ASDEX Upgrade and DIII-D using the edge fluid codes EDGE2D-EIRENE (JET and DIII-D), SOLPS (JET and ASDEX Upgrade) and UEDGE (DIII-D)
Comparison of actual and code-predicted (synthetic) measurements to validate numerical solutions ⇒ post-process solutions for underlying physics
Development of diagnostics and data analysis techniques for JET, ASDEX Upgrade and DIII-D ⇒ transfer to ITER

Iván Paradela Pérez:
(2021)
Juuso Karhunen: (2018)
Aaro Järvinen: (2015)

Updated: 23.1.2024
Published: 10.1.2019

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Scrape-off layer and plasma-wall interaction

Fluid and trace-impurity Monte Carlo codes

Research

Doctoral dissertations

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