The major increase in discharge duration and plasma energy in a next step DT fusion reactor will give rise to important plasma-material effects that will critically influence its operation, safety and performance. Erosion will increase to a scale of several centimetres from being barely measurable at a micron scale in today's tokamaks. Tritium co-deposited with carbon will strongly affect the operation of machines with carbon plasma facing components. Controlling plasma-wall interactions is critical to achieving high performance in present day tokamaks, and this is likely to continue to be the case in the approach to practical fusion reactors. Recognition of the important consequences of these phenomena stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER), and significant progress has been made in better understanding these issues. The paper reviews the underlying physical processes and the existing experimental database of plasma-material interactions both in tokamaks and laboratory simulation facilities for conditions of direct relevance to next step fusion reactors. Two main topical groups of interaction are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation and (ii) tritium retention and removal. The use of modelling tools to interpret the experimental results and make projections for conditions expected in future devices is explained. Outstanding technical issues and specific recommendations on potential R&D avenues for their resolution are presented.

/pdf/plasma-material-interactions-in-current-tokamaks-and-their-1a6iwv89x6.pdf

Plasma{material interactions in current tokamaks and their implications for next step fusion reactors

Non-Pd BCC alloy membranes for industrial hydrogen separation

Edge-localized-modes (ELMs) are a ubiquitous feature of H-mode in tokamaks. When gradients in the H-mode transport barrier grow to exceed the MHD stability limit the ELM instability grows explosively, rapidly transporting energy and particles onto open field lines and material surfaces. Though ELMs provide additional particle and impurity transport through the H-mode transport barrier, enabling steady operation, the resulting heat flux transients to plasma facing surfaces project to large amplitude in future low collisionality burning plasma tokamaks. Measurements of the ELM heat flux deposition onto material surfaces in the divertor and main chamber indicate significant broadening compared to inter-ELM heat flux, with a timescale for energy deposition that is consistent with sonic ion flow and numerical simulation. Comprehensive ELM simulation is highlighting the important physics processes of ELM transport including parallel transport due to magnetic reconnection and turbulence resulting from collapse of the H-mode transport barrier. Encouraging prospects for ELM control and/or suppression in future tokamaks include intrinsic modes of ELM free operation, ELM triggering with frequent small pellet injection and the application of 3D magnetic fields.

Edge-localized-modes in tokamaksa)

This paper reviews recent results of the study of dust in magnetic fusion devices. Assessment of the role of dust in current fusion devices and ITER is presented. Dust diagnostics, main experimental results, different theoretical aspects of dust in fusion plasmas, as well as the comparison of theoretical estimates and numerical simulations with available experimental data are discussed. Some limitations of current theoretical models of dust–plasma interactions and the gaps in current experimental and theoretical approaches to dust study in fusion devices are considered. Possible directions for further advancements are suggested.

https://iopscience.iop.org/article/10.1088/0741-3335/53/8/083001/pdf

Dust in magnetic fusion devices

To assist in the development of nuclear fusion as a viable commercial power source, preparation is underway for the fusion demonstration reactor (DEMO), which will build on the work of ITER, the international experimental fusion reactor. Like other advanced nuclear energy systems, DEMO must satisfy several goals including a high level of public and worker safety, low environmental impact, high reactor availability, a closed fuel cycle and the potential to be economically competitive. Yet there are still large scientific and technological safety gaps between the on-going ITER project and DEMO that will need to be addressed. Here we review international fusion safety research and development relevant to DEMO, following the lessons learned so far from ITER. We identify the main scientific and technological safety gaps, drawing on knowledge from the development of fission energy, in particular Generation IV (Gen-IV) fission reactors. From this survey, we discuss the corresponding implications for the design and operation of DEMO. Following on from ITER, a fusion demonstration reactor will be needed to showcase the commercial viability of fusion energy. To guide preliminary design considerations, this Review explores safety gaps that must be filled between current fission reactors, ITER and future fusion reactors.

Identification of safety gaps for fusion demonstration reactors

An overview of safety and environmental considerations in the selection of materials for fusion facilities

Within the framework of the International Energy Agency, an international collaborative study on fusion radioactive waste has been initiated to examine the back end of the materials cycle as an imp...

The back end of the fusion materials cycle

Russian concept for a DEMO-S demonstration fusion power reactor

Within the framework of the International Energy Agency (IEA), an international collaborative study on fusion radioactive waste has been carried out over the past several years to examine the back-end of the material cycle. This activity is important to maximize the environmental benefits of fusion as a source of energy. Fusion devices have certain characteristics that make them environmentally friendly devices. In previous studies, an integrated approach to the management of fusion materials back-end was proposed, starting from the removal of components from the power plant, to the reuse of materials through recycling and clearance, or the disposal of the low-level waste in repositories. Recycling and clearance procedures pose many technical questions. Several important technology-related issues were identified and are presented. The paper discusses these issues and considers the requirements to the materials and components permitting their clearance or recycling

B.N. Kolbasov

Papers

An overview of safety and environmental considerations in the selection of materials for fusion facilities

The back end of the fusion materials cycle

Russian concept for a DEMO-S demonstration fusion power reactor

Open Technological Questions Of The Back-End Of The Fusion Materials Cycle

On use of beryllium in fusion reactors: Resources, impurities and necessity of detritiation after irradiation