Material surface damage by quasistationary compression plasma flow action

Abstract

In many experiments plasma guns have been used to study the possibility of lowering the erosion due to disruptions and edge localized modes (ELMs) of great interest for the International Thermonuclear Experimental Reactor (ITER) safe operation. Modification of silicon single crystal surfaces by the action of supersonic compression plasma flow (CPF) generated by magnetoplasma compressor (MPC) has been studied. MPC plasma flow parameters (1 MJ/m2 in 0.1 ms) simulated transient peak thermal loads during Type I ELMs and disruptions. Analysis of the target’s erosion, brittle destruction, melting processes and dust formation has been performed. The layer with some of regular structures (rhombic on the Si (111) and rectangular on Si (100) surface) can be separated from the underlying bulk, being ejected as the blocks from the surface. These surface phenomena are results of specific conditions during CPF interaction with target surface and differential stresses produced in a near surface layer. High plasma flow energy density, large dynamic pressure, thermodynamic parameters gradients and induced magnetic field on treated surfaces cause rapid heating and melting of the surface layer, prolonged existence of the molten layer and fast cooling and recrystallisation, as well as surface fracturing.