Influence of a magnetic field on plasma energy transfer to material surfaces in edge-localized mode simulation experiments with QSPA-M

Abstract

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.

Parameters of Hydrogen Plasma Streams in Qspa-M and Their Dependence on External Magnetic Field

“…Integral gas supply of QSPA discharge was about 530 cm 3 H 2 at atmosphere pressure. The detailed description of facility and first experimental results are given in [7,8].…”

“…The detailed measurements of plasma density were carried out at U discharge = 10 kV. This working voltage corresponds to maximal energy in the present experimental series and it is typically applied for exposures of tungsten targets in ELM simulation experiments [8]. Fig.…”

“…The maximal energy density is over than Q = 0.75 MJ/m 2 and it reached at U discharge = 10 kV. The interaction of plasma with the target surfaces and the energy transfer from the plasma stream to the target surface are discussed in [8].…”

“…The QSPA-M plasma accelerator, as compare with other available QSPA devices, is equipped with magnetic coils creating the external longitudinal B-field up to 1T. Ability of QSPA-M to operate with additional external strong external magnetic field allows simulation of the divertor plasma flows along the Bfield linesduring the transient events in ITER and DEMO reactors and predictive testing of candidate materials under powerful plasma exposures [7][8][9].…”

Discharge Parameters of Magnetoplasma Compressor: Effect of External Axial Magnetic Field

“…High-current discharges that generate dense plasma flows have many applications in different areas of studies, including plasma-surface interaction and astrophysics. Quasistationary plasma accelerators (QSPAs) [1,2] that are capable of generating powerful plasma streams now contain additional external magnetic field systems. It allows for studying the effect of an additional magnetic field on plasma flow parameters and simulating conditions close to those at the divertor plates of ITER under transient events [1][2][3].…”