Study of the damageability of materials using a plasma focus device “Vikhr”

The results of irradiation of metal (nickel alloy Inconel 718) and semiconductor (silicon single crystal) materials by helium ions and helium plasma pulsed beams using a plasma focus (PF) device “Vikhr” are presented. The damageability and radiation-thermal stability of the materials exposed to high-power pulsed helium ion beams of the working gas and high-temperature plasma have been studied and assessed in a wide range of the radiation power density (pulse duration 10^-8 - 10^-6 sec). Experiments showed that both materials exposed to “soft” irradiation (q = 10⁶ -10⁷ W/cm²), which did not lead to complete surface melting, underwent the process of sputtering mainly in the areas containing mechanical defects. However, for each of the materials, local areas of melting of the surface layer are observed, which is associated with an irregular distribution of the particle density over the cross section of the radiation flux incident on the target sample. A thin film was found on the surface of both materials: SiO₂ oxide on a Si single crystal; and a film resulted from the interaction of the alloy components with residual gases in the PF chamber and chemical elements deposited earlier on the surface of Inconel 718 alloy. Irradiation in a “hard” mode (q = 10⁸ - 10⁹ W/cm²) with a large number of puls shots leads to melting and partial evaporation of the surface layer with the formation of a wave-like relief and microstructural defects such as ridges, craters, bubbles and microcracks after crystallization of the melt. A solidified surface layer becomes very brittle, easily separates from the non-melting Si base and breaks up into small particles like a powder. We have shown that after the beam-plasma treatment, the surface layer of silicon contains the elements occurred in other structural and functional materials located in the PF chamber. At each pulsed discharge, they are deposited on the irradiated surface of Si single crystal. Experiments and studies have also shown that a device “Vikhr” is promising for simulation of extreme conditions of exposing material to ionizing radiation, which are realized in thermonuclear devices with magnetic and inertial plasma confinement, as well as for creating more “soft” radiation regimes characteristic of the radiation fluxes of the space environment.

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