The features of plasma energy transfer to material surfaces during plasma–surface interactions (PSIs) in the presence of a strong magnetic field are investigated within the recently developed quasi-stationary plasma accelerator, QSPA-M. This novel PSI test-bed facility can reproduce edge localized mode (ELM) impacts, both in terms of heat load and particle flux to the surface, and provide plasma transportation in an external magnetic field, which mimics the divertor conditions. Investigations of energy transfer to the material surface have been performed for varied plasma heat load and external magnetic field values. Calorimetry, optical emission spectroscopy and high-speed imaging were applied for PSI characterization. For perpendicular plasma incidence, it has been shown that the transient plasma layer is formed in front of the surface by the stopped head of the plasma stream even for rather small plasma heat loads, which do not result in surface melting. The plasma density in this near-surface layer is much higher than in the impacting stream. It leads to the arisen screening effect for energy transfer to the surface. For B  =  0, the thickness of the screening layer is less than 3 cm, but it increases to 15 cm when B  =  0.8 T. The shielding effect due to the formation of a dense plasma layer in front of the exposed surface should be favorable for material performance, being important for decreasing the overall erosion of plasma-facing components during a large number of repetitive ELMs.

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In this report concept of new generation QSPA with external B-field up to 2 T has been discussed and novel test-bed facility, which recently constructed in Kharkov IPP NSC KIPT, has been described. It allows new level of plasma stream parameters and its wide variation in new QSPA-M device, as well as possible combination of steady state and pulsed plasma loads to the materials during the exposures. First plasma is recently obtained. Careful optimization of the operational regimes of the plasma accelerator's functional components and plasma dynamics in the magnetic system of QSPA-M device has been started approaching step by step the necessary level of plasma parameters and their effective variation. The relevant results on plasma stream characterization are presented. Energy density distributions in plasma stream have been measured with calorimetry. Spectroscopy and probe technique have been also applied for plasma parameters measurements. The obtained results demonstrate ability of QSPA-M to reproduce the ELM impacts in fusion reactor both in term of heat load and particle flux to the surface.

This paper is devoted to plasma-surface interaction issues at high heat-loads which are typical for fusion reactors. For the International Thermonuclear Experimental Reactor (ITER), which is now under construction, the knowledge of erosion processes and the behaviour of various constructional materials under extreme conditions is a very critical issue, which will determine a successful realization of the project. The most important plasma-surface interaction (PSI) effects in 3D geometry have been studied using a QSPA Kh-50 powerful quasi-stationary plasma accelerator. Mechanisms of the droplet and dust generation have been investigated in detail. It was found that the droplets emission from castellated surfaces has a threshold character and a cyclic nature. It begins only after a certain number of the irradiating plasma pulses when molten and shifted material is accumulated at the edges of the castellated structure. This new erosion mechanism, connected with the edge effects, results in an increase in the size of the emitted droplets (as compared with those emitted from a flat surface). This mechanism can even induce the ejection of sub-mm particles. A concept of a new-generation QSPA facility, the current status of this device maintenance, and prospects for further experiments are also presented.

This paper presents experimental studies of plasma-surface interactions during powerful plasma impacts of a quasi-stationary plasma accelerator (QSPA) on the Sn capillary porous systems (CPSs) in conditions simulating disruption and edge localized modes (ELM) like loads. Experiments were carried out using two QSPA devices. ELM-like plasma exposures were performed with QSPA-M test-bed facility. A large-scale QSPA Kh-50 device was used to simulate plasma disruptions and giant ELMs. Variation of the plasma stream energy density has been performed to study the onset of vapour shield. It is shown that during plasma exposures of a Sn-CPS target with the QSPA plasma load <1 MJ m −2 , single dust particles traces have been registered. A further increase in the heat load leads to the splashing of the eroded material. For ELM-like impacts, a rather weak melt motion was observed on the target surface. A post-mortem analysis has shown that the CPS structure was not destroyed in the course of many repetitive ELM-like pulses. Surface morphology has changed from a smooth surface to corrugation structures with the formation of some cavities in mesh cells due to the influence of the surface tension and capillary effects. Spectral lines of Sn I and Sn II have been identified by optical emission spectroscopy in the near-surface plasma. A plasma shield, that consists mostly of Sn neutrals appears at Q ∼ 0.1 MJ m −2 . An increase in the surface heat load resulted in the intensive emission of Sn II lines, which started to be observed at Q ∼ 0.3 MJ m −2 . The plasma electron density near the surface increases significantly at Q > 0.5 MJ m −2 , which corresponds to the strong vapour shielding of the exposed surface. A comparison between the obtained results on the vapour shielding of Sn CPS and available numerical simulation using the TOKES code has been performed.