Power deposition behavior of high-density transient hydrogen plasma on tungsten in Magnum-PSI

Abstract

The lifetime of plasma-facing components (PFCs) will have a strong influence on the efficiency and viability of future fusion power plants. However, the PFCs suffer from thermal stresses and physical sputtering induced by edge-localized modes (ELMs). ELMs in future fusion devices are expected to occur with a high plasma density compared to current day devices such that coupling of recycling neutrals and plasma ions will be strong. Because of the scale hierarchy of future fusion devices compared to the present ones, the influence of this coupling is difficult to predict. Here, we investigate the ELM-like hydrogen plasma induced heat loads on tungsten in the linear device Magnum-PSI, producing ∼1 ms plasma pulses with electron densities up to 3.5 × 10 21 m −3 . A combination of time-resolved Thomson scattering and coherent Thomson scattering was used to acquire plasma parameters in front of the target. Moreover, a fast infrared camera coupled to finite element thermal analyses allowed to determine the deposited heat loads on the target. We found a significant inconsistency between the plasma power calculated with a conventional collisionless sheath model and the absorbed power by the target. Moreover, plasma stagnation upstream and plasma cooling downstream were observed during the pulses. The observations are explained based on ionization and elastic collisions between the recycling neutrals and plasma ions. The results highlight the impact of plasma-neutral interaction on the power deposition behavior of ELM-like hydrogen plasma on tungsten.

Influence of porosity and blistering on the thermal fatigue behavior of tungsten

“…Because of the low H 2 density and high electron density in Mangum-PSI, both of which inhibit H 2 + /H 3 + formation, the ion population is predominantly H + [35,36]. This is consistent with the agreed heat fluxes from calorimetry and TS data [32]. The peak H + ion energy was ∼6 eV and the exposure time was ∼10 4 seconds.…”

“…At a surface temperature of 750 • C, a similar ΔT induced ∼0.6% von Mises plastic strain per cycle according to finite element calculation [31]. Table 2 summarizes the key loading parameters, in which the H + ion fluence was calculated with a collisionless sheath model using the measured TS data [32]. In the calculation, T e = T i was assumed as justified by coherent TS measurements [33,34].…”

Reduction of pulsed particle load with dynamic pressure induced by transient recycled neutral flux

“…The present experiments performed in the high p n cases seem to demonstrate heat pulse mitigation with a completely different mechanism from the present low p n cases and [14]. Recycled neutral particles have difficulty interacting with pulsed plasma because the collisions of recycled particles with background neutral particles are comparable to the collisions with pulsed ions in high p n cases, as discussed in section 4.1.2.…”

“…To discuss the mitigation mechanism of the pulse, a previous study on power deposition by transient plasma should be covered. A fast infrared camera coupled to a finite element analysis was used to acquire the heat flux deposited by the pulsed plasma inputs on the Magnum-PSI target in [14]. Clear energy loss was observed in the pulsed plasma with high n e and the possible interpretations are as follows: Owing to the enhanced recycling of particles in high n e cases, T e decreases due to ionization in front of the target.…”

“…Such experiments are realized in the linear plasma device Magnum-PSI because of its high performance for steady-state plasma generation with a particle flux of 10 23 -10 25 m −2 s −1 and high-density pulsed plasma production [12,13]. The density dependence of the pulsed heat load was studied in Magnum-PSI [14], which indicated the saturation of the peak heat load into the target in a high-density regime. Localized enhancement of the ionization and charge exchange (CX) processes was implied to constitute the energy-loss mechanism.…”