Hot electron target interaction experiments at the GOL-3 facility

Abstract

At the GOL-3 facility, experiments on the interaction of powerful hot electron streams with various materials have been performed. For energy densities of the hot electron stream above 10 MJ/m2 an explosive-like erosion was observed, which at energy densities of 30 MJ/m2 reaches 500 mu m for fine grain graphite and 200 mu m for tungsten. Under these conditions, the corona of the carbon vapour cloud has temperatures below 1.2 eV and densities up to 1017 cm-3. It propagates along the magnetic field lines with maximum velocities of 2.1*106 cm/s. The longitudinal and transverse (along and across magnetic field lines) vapour velocities of the colder bulk plasma are about 106 cm/s. A model for explosive-like erosion was developed and tested against the GOL-3 results. For graphite the destruction threshold is 10 kJ/g. This value is considerably lower than the vaporization enthalpy of 20.5 kJ/g for three atomic vaporization. The validated model was applied to a numerical analysis of the occurrence of explosive-like erosion for ITER disruptions and runaway electrons. If the energy density of the runaways remains below 30 MJ/m2, explosive-like erosion of graphite occurs for electron energies below 20 MeV. For the energetic tail of Maxwellian plasma electrons with temperatures up to 20 keV and power densities of 10 MW/cm2 without any angular spread, explosive-like erasion becomes comparable to erosion by vaporization

Brittle Destruction of Carbon Based Materials Under Off-Normal ITER-FEAT Conditions

“…The corresponding volumetric heat load used for the numerical simulation was calculated by a Monte Carlo algorithm [10]. Onset of brittle destruction occurs at about 10 MJ/m 2 in agreement with the experimental results obtained at the GOL-3 facility [11]. At 14 MJ/m 2 the average experimental value of brittle destruction is about 70 microns.…”

Comparison of tungsten modification after irradiation at different facilities for PSI studies

“…With loads of 12 MJ/m 2 , the erosion depth after one shot can exceed 200 μm (GOL-3 [12]). The big erosion depth at plasma loads comparable with the lowest estimations of ITER (and DEMO) disruptions and transient events show that big tokamaks have no room for error.…”

Magnetohydrodynamically stable plasma with supercritical current density at the axis

“…The specific energy density within the beam-heated zone in GOL-3 reached 100 MJ/m 2 in special experiments aimed at simulation of plasma-wall interactions under heat loads typical for major disruptions at ITER and reactor-grade tokamaks. 26 At a disruption, this energy destroys in-vessel components that are accidentally touched by the plasma. For long experimental runs at GOL-3, disruption probability can be estimated as 0.2%.…”