Plasma material interactions

The interdisciplinary field of plasma material interactions encompasses all physical processes that lead to the exchange of particles, momentum and energy between plasmas and condensed matter bodies. The latter can be dust grains or droplets embedded in plasmas and solid or liquid material boundaries surrounding plasmas. In the case of confined hot dense plasmas, diverse microscopic processes are capable of modifying not only the plasma properties but also the material properties or topologies. Given the increase of the plasma energy content and discharge duration in next generation tokamak devices such as ITER (currently under construction) and DEMO (in the planning phase), plasma material interactions constitute a field of paramount importance for magnetic confinement fusion. In particular, plasma material interactions (hereafter PMI) are tightly connected to burning plasma performance issues, heat exhaust issues, component lifetime issues, diagnostic degradation issues and safety issues.

The following ITER- and DEMO-relevant PMI topics are investigated by the group with a strong synergy of theoretical, computational and experimental efforts:

• Dust transport and survivability (theory, modelling, experiments)
• Metallic melt motion (theory, modelling, experiments)
• Emissive sheaths in magnetized plasmas (theory, modelling)
• Dust generation (theory, modelling, experiments)
• Dust adhesion and remobilization (theory, modelling, experiments)

These scientific problems require in-depth knowledge of disparate physics disciplines, namely plasma physics, electron emission physics, computational fluid dynamics, contact mechanics, surface physics, condensed matter physics, impact mechanics and atomic physics. Over the years, the group has built a diverse expertise that is complemented by an extended network of international collaborations.

Integration

• The group’s work is fully integrated into the roadmap of the EUROfusion Consortium for the realization of fusion energy. From 2014 up to date; the group has successfully
  • undertaken multiple tasks within the PFC, MST-1, JET-1 work packages (2014-2020) and the PWIE, TE, DES work packages (2021-date)
  • led a high-priority enabling research project
  • participated in a high-priority enabling research project  
• The group’s work is fully integrated into the research plan of the ITER organization as well as the research and development activities for ITER.
  • The group’s work on melt layer motion 09/2016-09/2020 was conducted within the framework of an Implementing Agreement (IO/IA/16/4300001384) established under the Cooperation Agreement between the ITER Organization and KTH.
  • The group has received a one-year service contract, 10/2020-10/2021, by the ITER Organization for “Simulation of disruption transient-induced beryllium melt splashing” (IO/20/CT/4300002230).
  • Part of the group’s future work on melt layer motion will be conducted within the framework of an Implementing Agreement (IO/IA/22/430000xxxx) established under the Agreement on Academic and Scientific Cooperation between the ITER Organization and KTH (Ref.LGA-2021-A-75).
  • The group’s permanent members have been recognized as experts in the Scrape-Off-Layer & Divertor (DivSOL) Topical Group of the International Tokamak Physics Activity (ITPA) framework under the auspices of ITER.
  • The group’s permanent members and doctoral students have given multiple invited talks at DivSOL ITPA meetings.
• The group’s work is fully integrated into the research plan for the design of the European DEMO fusion reactor.
  • The group participates in the TSVV (Theory, Simulation, Validation, Verification) Task 7 “Plasma-Wall Interaction In DEMO” of the EUROfusion Consortium (2021-2025) whose primary objectives are to establish an integrated modelling suite to describe PMI in DEMO, supply safety-relevant information for DEMO reference scenarios and provide guidelines for the DEMO conceptual design review.
  • Through the long term TSVV Task, the group’s MIGRAINe dust dynamics code and MEMENTO macroscopic melt motion code will be part of the EUROfusion standard software products that are designed to benefit a wide range of users, well beyond the team of code developers, with free availability.
  • The group is successfully participating in the DES work package of the EUROfusion Consortium whose mission is to support the DEMO Central Team advance the technical basis of DEMO in order to arrive to a complete integrated system concept design so that detailed assessments of technical feasibility, reliability, safety, maintainability and costs can be progressively undertaken.
• The group’s experimental activities are performed in the largest European and International tokamak devices and linear plasma devices. In particular, the group
  • has proposed and designed multiple experiments dedicated to dust survivability, transport and remobilization that were performed in tokamaks (ASDEX Upgrade, DIII-D, COMPASS, TEXTOR) and linear plasma devices (Magnum-PSI, Pilot-PSI, GyM),
  • has proposed and designed multiple experiments dedicated to macroscopic melt motion that were performed in tokamaks (ASDEX Upgrade, DIII-D), 
  • has participated in the modelling of multiple experiments dedicated to macroscopic melt motion (JET, ASDEX Upgrade, WEST)

Highlights

• Development of the MIGRAINe dust dynamics code including validation of different embedded theoretical models and applications to ITER scenarios.
• Development of the MEMENTO metallic melt motion code (significantly refining the physics model and significantly upgrading the numerical capabilities of the MEMOS 3D code) including extensive validation against tokamak experiments and applications to ITER as well as DEMO scenarios.
• Development of a novel experimental technique that allows for the controlled study of dust remobilization and adhered dust - plasma interaction.
• Development of customized ANSYS set-ups that are capable of simulating pressure-driven melt ejection during arcing and metallic melt flows over plasma-facing component edges.
• Development of a theoretical model for the self-consistent description of the replacement current driving melt layer motion.
• Development of an analytical model of particle and heat flux collection by dust immersed in dense magnetized plasmas (regime of strong magnetized electron collection and thin-sheath ion collection).
• Construction of an accurate semi-empirical analytical expression for the escaping thermionic current from inclined space-charge limited sheaths based on particle-in-cell simulations.
• First experimental observation of the ITER/DEMO-relevant phenomena of wetting-induced coagulation, intermetallic compound formation at contact and diffusion bonding at contact.
• First measurements of the dust-wall adhesive force and the velocity restitution curves of dust wall mechanical collisions.

SPP Team