Latest results of Eurofusion plasma-facing components research in the areas of power loading, material erosion and fuel retention

Abstract

The interaction between the edge-plasma in a fusion reactor and the surrounding first-wall components is one of the main issues for the realisation of fusion energy power plants. The EUROfusion Work Package on plasma-facing components addresses the key areas of plasma-surface interaction in view of ITER and DEMO operation, which are mostly related to material erosion, surface damage and fuel retention. These aspects are both investigated experimentally (in tokamaks, linear plasma devices and lab experiments) and by modelling. Here, selective results regarding the main research topics are presented: in the area of tungsten (W) surface modifications, the interplay between W fuzz formation and W fuzz erosion depends strongly on the local plasma and surface conditions, as demonstrated by tokamak experiments. Complementary, experimental findings on the dependence of erosion on the surface structure in lab-scale experiments have led to the successful implementation of surface structure effects in numerical modelling. The qualification of ITER-like monoblocks at high fluences of up to 1031 D m−2 in linear plasma facilities has shown no visible damages at cold plasma conditions. However, experiments with simultaneous plasma and pulsed heat loading (edge-localized modes simulations) show that synergistic effects can lower the W damage thresholds. Additionally, fuel retention studies show that nitrogen as a plasma impurity increases the fuel retention in W, and that deuterium implanted in the surface of W is capable of stabilizing displacement damages caused by neutron damage. Finally, the implications of these results on ITER and DEMO operation are discussed and an outlook on follow-up experiments is given: the results indicate that there are possible impacts on the ITER divertor lifetime and tritium removal. Other areas like the divertor shaping and the erosion need additional investigations in the future to quantify the impact on ITER and DEMO operation.

The density and pressure of helium nano-bubbles encapsulated in silicon

“…An equation of state, derived entirely from experimental values, suitable for deducing the pressure of fluid helium from a given density, expresses the molar volume V M as a function of pressure. This relation, equation (7) of [37] is…”

“…The problems caused by confined and compressed helium are fast becoming a major issue in nuclear fusion materials research [3,5]. Encapsulated helium bubbles not only cause embrittlement and fatigue [6] but also damage the plasma-facing surfaces forming coral-like nano-structures that could erode into the plasma, degrading its quality, cooling and suppressing the fusion reaction [7]. These considerations motivated the extensive studies of such bubbles in different host materials with the object of both understanding bubble structure and dynamics [8,9] as well as determining the helium density and hence the pressure that an encapsulated bubble exerts on the boundary matrix material.…”

The Effect of a Small Helium Addition on the Plasma-Surface Interaction in Qspa

“…Therefore, it is very important to study the interaction of helium and hydrogen-helium plasmas with PFMs. It is well-known that He has a damaging impact on the surface morphology during plasma exposure, for example, inducing tungsten (W) fuzz, blisters, helium bubbles and other [1][2][3][4][5]. Nevertheless, the synergistic effects of tungsten exposure to combined particle fluxes of different kinds (hydrogen, helium, etc.)…”

Features of Modifications in the Re-Solidified Surfaces of Advanced Materials Due to High-Power Plasma Pulses

“…Tungsten is a primary material that will be used as a first-wall and a divertor armour in fusion devices like ITER and DEMO due to its high melting point, high thermal conductivity, low sputtering yield, and tritium retention [3,4]. The development of advanced tungsten products made using various production/densification technologies, i.e., forging and rolling, additive manufacturing (AM), W-based alloys, W-composites, and W-fibres requires thorough testing and characterization under harsh fusion-relevant conditions (including H isotopes, He, etc) [1,3,[5][6][7].…”