A. S. Arakcheev

Heating of tungsten target by intense pulse electron beam

A test facility for experimental simulation of transient heat loads in ITER divertor with the use of high power electron beam is developed at the Budker Institute of Nuclear Physics. This report presents an experimental study of the absorption of the electron beam with an incident heat power flux of 10-50 GW/m2 on the area of about 2 cm2 of a tungsten target. The electron beam has duration of 0.1-0.3u2005ms and electron energy of 80-95 keV, Diagnostics for measuring of the beam parameters on the target are briefly discussed. Results of measurement of the beam profile and calorimetry of beam energy deposited in tungsten sample at ELM-like heat load are presented.

Observation of dust particles ejected from tungsten surface under impact of intense transient heat load

A test facility for experimental simulation of transient heat load expected for ELMs type I events in ITER is developed at BINP SB RAS. Dynamics of tungsten particles in the ablation plume is investigated by small-angle light scattering technique and using fast CCD and ICCD cameras. The threshold of intense particle generation, sizes and velocities of particles ejected from the surface are estimated.

Observation of the tungsten surface damage under ITER-relevant transient heat loads during and after electron beam pulse

Wide-area (2u2005cm2) high-power (up to 7 MW) submillisecond electron beam source was applied for generation of intense pulsed heat loads on tungsten sample. Various diagnostics sets were used for in-situ research of the surface damage: IR imaging of the front view of the target, capturing of the reflection pattern of continuous wave laser radiation, recording of intensity of thermal radiation from several spots of the surface. Sample was exposed to a various heat loads near and above melting threshold. Formation of the crack network on the surface and its development with successive pulses was observed. Two-dimensional temperature distribution was obtained after heating at the cooling stage. Melting and spalling of material were shown on severe damaged target. Propagation of the cracks along the surface at a depth of 0.1 – 0.2u2005mm was revealed with transverse microsections. Circular motion of the molten layer was found with subsequent exposures.

Numerical model of high-power transient heating of tungsten with considering of various erosion effects

Surface melting of tungsten under exposure to a pulsed electron beam was simulated numerically, the evaporation process taken into account. The calculation is based on the experimental time dependence of the total beam power. The model of the tungsten heating process is based on solving the two-phase Stefan problem. The position of the phase boundary depends on discontinuous time- and space-nonlinear coefficients and boundary conditions. The aim of the study is to provide a detailed resolution of the heat flow deep into the material with a fine spatial grid step. As compared with the size of the tungsten plate, the heating depth is very small. The problem statement under consideration is multiscale. Further expansion of the model involves taking into account microcracks. Micro-cracks occur during the cooling process after exposure and affect the temperature of the tungsten surface during the subsequent heating process. The article presents a modeling of cracks of different geometries typical for this process. The results of the calculations correlate with the experimental data obtained on the experimental test facility BETA at BINP SB RAS.

Expansion of dense plasma formed on solid target exposed to focused electron beam

Performance of flash radiography units implies a high spatial resolution. Thus, focused electron beams are utilized to produce bremsstrahlung x-ray at the solid target. Strong heating of the target up to 1-10 eV temperature and formation of dense plasma can lead to beam disruption. In case of multi-pulse operation mode of radiography unit the plasma produced by the first pulse can strongly affect subsequent pulses. In present work we utilize the model of Zeldovich and Raizer to estimate the electron density in the target plasma. The typical parameters of radiography units based on linear induction accelerators is considered. It is shown that electron density in plasma expanding after first pulse is high enough to affect subsequent electron beams.