[en] A high-power edge-localized mode (ELM) striking onto divertor components presents one of the strongest lifetime and performance challenges for plasma facing components in future fusion reactors. A high-repetition-rate ELM replication system has been constructed and was commissioned at the Magnum-PSI linear device to investigate the synergy between steady state plasma exposure and the large increase in heat and particle flux to the plasma facing surface during repeated ELM transients in conditions aiming to mimic as closely as possible those in the ITER divertor. This system is capable of increasing the electron density and temperature from ∼1 × 10²⁰ m⁻³ to ∼1 × 10²¹ m⁻³ and from 1 to 5 eV respectively, leading to a heat flux increase at the surface to ∼130 MW m⁻². By combining Thomson scattering measurements with heat fluxes determined using the THEODOR code, the sheath heat transmission factor during the pulses was determined to be ≈7.7, in agreement with sheath theory. The heat flux is found to be linearly dependent upon the strength of the magnetic field at the target position, and, by adapting the system to Pilot-PSI, tests at 1.6 T showed heat fluxes of more than 600 MW m⁻². This gives confidence that with the installation of a 2.5 T superconducting magnetic solenoid at Magnum-PSI the heat flux will reach the ITER-relevant gigawatt per square metre heat flux regime. (paper)

[en] Tungsten samples were exposed to combined steady state and edge localised mode transient replication experiments in a linear plasma device; either in combined hydrogen plasma and high powered laser exposures at Magnum-PSI or steady state hydrogen plasma and superimposed plasma pulses created using a capacitor bank in Pilot-PSI. With each transient the surface temperature of the sample was elevated above the melting point creating a shallow molten layer. An apparent heat transport reduction in the near surface layer increases as a function of pulse number. Scanning electron microscopy analysis of the samples shows large scale grain enlargement down to several hundred to thousand micrometers below the surface as well as melt layer motion due to evaporative recoil from the molten surface. In the ITER divertor this would lead to severe embrittlement and enhanced erosion of the tungsten surface leading to reduced lifetimes for the plasma facing material. (paper)

[en] Transient heat pulses with triangular, square, and ELM-like temporal shapes are investigated in order to further understand how transient plasma instabilities will affect plasma facing components in tokamaks. A solution to the 1D heat equation for triangular pulses allows the peak surface temperature to be written analytically for arbitrary rise times. The solution as well as ANSYS simulations reveal that a positive ramp (maximum rise time) triangular pulse has a higher peak surface temperature by a factor of $\sqrt{2}$ compared to that from a negative ramp (rise time = 0) pulse shape with equal energy density, peak power, and pulse width. Translating the results to ITER, an ELM or disruption pulse with the shortest rise time is the most benign compared to other pulse shapes with the same peak heat flux and same energy density. (paper)

[en] The linear plasma generator Magnum-PSI was designed for the study of plasma–surface interactions under relevant conditions of fusion devices. A key factor for such studies is the knowledge of a set of parameters that characterize the plasma interacting with the solid surface. This paper reports on the electrical diagnosis of the plasma beam in Magnum-PSI using a multi-probe system consisting of 64 probes arranged in a 2D square matrix. Cross-section distributions of floating potential and ion current intensity were registered for a hydrogen plasma beam under various discharge currents (80–175 A) and magnetic field strengths (0.47–1.41 T in the middle of the coils). Probe measurements revealed a high level of flexibility of plasma beam parameters with respect to the operating conditions. (paper)