ELM simulation experiments on Pilot-PSI using simultaneous high flux plasma and transient heat/particle source

Abstract

Edge Localized Modes (ELMs) are a major concern for the lifetime of the divertor plasma-facing materials (PFMs) in ITER. The very high localized heat fluxes will lead to material erosion, melting and vaporization. In addition, the repetition of such thermal shocks can lead to a degradation of the material thermomechanical properties. In ITER, the PFMs will be submitted to both the steady state detached divertor plasma and the intense heat and particle fluxes during ELMs. In such a situation, the ELMs will interact with a surface modified by the intense fluxes of low energy ions, which are known to lead to strong modifications of the surface morphology. Moreover, the surface will be in equilibrium with the steady-state plasma and the nearsurface will be loaded with helium and hydrogen isotopes. Such a situation might lead to strong synergistic effects which need to be investigated in details. A new experimental setup is being developed at FOM Rijnhuizen for ELM simulation experiments with relevant steady-state plasma conditions and transient heat/particle source, allowing those effects to be studied in a selfconsistent manner. The initial setup is based on the Pilot-PSI linear device and allows the superimposition of a transient heat/particle pulse to the steady-state heat flux plasma. Energy densities as high as 1MJ.m-2 have been reached for a pulse duration of 1ms. In this contribution, we report on the first experiments were made to investigate the effect of the combined steady-state/pulsed plasma on polycrystalline tungsten targets. Postmortem analysis of the targets was done by Scanning Electron Microscopy (SEM). Fast visible imaging was used to determine in-situ the threshold for tungsten release from the surface.

Modelling Thermal Shock Based Cracking Behaviour of Armour Material for Fusion Reactor

“…This simulation result follows the numerical result following the reported analytical in Carslaw and Jaeger [12]. For the one-dimensional heat flux conduction issue experienced when chilling off sample 1D composite whose infinitely huge surface is exposed to heat and was affirmed by surface temperature estimations by quick infrared and noticeable imaging in the reported tests [13]. This result exhibits the temperature variation at different surface depths of the composite material as only the surface layer had gone through an oxidative temperature.…”

“…Average cracking elements were splitting and surface roughening because of plastic strains. At lower base temperatures, specifically beneath the pliable to fragile temperature, tungsten materials displayed basic resistance for crack progression [12][13][14][15][16][17].…”

Microstructural modifications in tungsten induced by high flux plasma exposure: TEM examination

“…Exposures to deuterium plasma were performed at the linear plasma generator Pilot-PSI [19,20], which delivers high-density, low-temperature plasmas mimicking the 'subdisplacement threshold' plasma wall interaction conditions expected in the ITER divertor. In this experiment, the energy of deuterium ions was ∼50 eV (controlled by negatively biasing the target), while energies in excess of 900 eV are required to initiate atomic displacement in W [21].…”

High heat flux capabilities of the Magnum-PSI linear plasma device

“…The pulse duration is about 1.3 ms and heat fluxes in excess of 1 GW·m −2 have been achieved in hydrogen, helium and argon. The system is aimed at studying the possibility of synergistic effects caused by the simultaneous exposure of a metallic surface to a divertor relevant high flux plasma and a transient heat/particle source [25]. On Pilot-PSI, the repetition rate is limited to one pulse per discharge because of the charging time of the capacitors.…”

“…For the lowest laser energy, surface roughening and the development of cracks at grain boundaries can clearly be seen. It should be mentioned that under otherwise similar laser loading conditions, no surface modifications can be observed in the absence of plasma exposure [26], outlining the possible strong role of hydrogen plasma exposure on the surface damage of tungsten as well as the importance of synergistic effects arising during simultaneous plasma/transients exposure [25]. Further studies will be carried out to compare the damage induced by laser and pulsed plasma heating, respectively, and elucidate the role of the increased particle flux during a plasma pulse on the surface response.…”