Test of divertor materials under simulated plasma disruption conditions at the SOM electron beam facility

Abstract

The SOM electron beam facility at the Efremov Institute at St. Petersburg was used for exploratory plasma stream target experiments under conditions aiming the thermal quench phase of ITER tokamak plasma disruptions. The SOM facility uses a vacuum diode with multipoint explosive emission cathode for e-beam formation and a downstream increasing magnetic field for beam transportation and focusing onto the target. The beam energy is around 100 keV. Pulse durations up to 200 μs and energy densities at the target up to 4.5 MJ/m 2 are achieved. Optical interferometry and spectroscopy allowed to study the formation and properties of the plasma formed from vaporized target materials in front of the target. Target erosion was also determined. For carbon erosion starts after reaching a threshold energy density value of 1 MJ/m 2. The onset of target plasma formation strongly depends on beam power density and for 2 MW/cm 2 starts only after 80 μs. Temperature and density of the target plasma remain low and the fraction of neutrals is high. Modeling was done with a radiation hydrodynamic code in one-dimensional planar geometry. Multifrequency radiation transport was treated in forward reverse transport approximation. The modeling results in terms of vapor shield formation, target plasma temperature and erosion are in good agreement with the experimental results. Vapor shield formation is negligible. The erosion is mainly determined by the power density of the unattenuated beam.