Diagnostics of the dynamics of material damage by thermal shocks with the intensity possible in the ITER divertor

Abstract

A novel BETA test facility (Beam of Electrons for materials Test Applications) was developed at the Budker Institute to study the erosion of materials directly during the impact of intense thermal shocks. A powerful (up to 7 MW) long pulse (100-300 μs) electron beam is applied for experimental simulation of fast transient heat loads with the intensity probable in the ITER divertor. The heat flux parameter on a target can be widely varied (F HF =10-300 MW m −2 s 0.5 ) from a value significantly below the melting threshold to a value much higher, within the area of about 1 cm 2 . The use of an electron beam to simulate the thermal impact on the material surface makes it possible to employ a variety of optical diagnostics for in situ observations of the dynamics of surface erosion processes during intense thermal shocks. These distinctive features make BETA a promising tool in the research of material surface erosion mechanisms and for experimental verification of various analytical and numerical models associated with these mechanisms. The first results obtained with this facility include fast (10 μs exposure) imaging of the heated target in the near-infrared range and in the reflected light of 532 nm continuous wave (CW) laser, visualization of ejected tungsten particles using fast ICCD and CCD cameras with the minimal exposure of 2 μs and 7 μs respectively. The dynamics of dust particles ejected from the heated surface is investigated using a multichannel recording of the light of 532 nm CW-laser scattered on the dust particles. The present paper describes the first results of use of two new in situ methods: continuous recording of light scattered from the tungsten surface and threedimensional tracking of tungsten particles using three viewing angles. The first method makes it possible to observe the dynamics of development of roughness and cracking of the polished tungsten surface, which manifest themselves as two successive processes separated by a large time delay. The second method allows us to track dust particles ejected from the melt layer, and thus determine the time and place of particle ejection from the surface.

Laser holographic interferometry of short ultraviolet radiation with high power density interaction with condensed metters

“…The study of such flows seems relevant both for solving problems of modern physics of a non-equilibrium spatially inhomogeneous plasma, and in connection with numerous technical problems, for example: developing new methods for generating and accelerating gas-plasma flows in plasma-laser accelerators and injectors [1][2][3][4][5], optimization of operating modes of plasma accelerators and electrodynamic devices where the erosion of an insulator and electrodes under the action of radiation determines the mass flow rate of the plasma-forming substance [6][7][8][9], process optimization in technological (photolithography, radiation surface hardening) and photochemical installations [10][11][12][13]. The interaction of powerful broadband radiation with matter accompanies the processes on the walls of thermonuclear facilities [14,15]. This explains the interest in these studies.…”