The Impact of Pulsed Helium Ion-Plasma Flows and Electron Beams Generated in the Plasma Focus Device on a Tungsten Single Crystal

Using the Plasma Focus PF-5M device, damageability, erosion, and structural changes in the surface layers of tungsten single-crystal samples caused by exposure to pulsed electron beams are studied in comparison with pulsed irradiation by combined flows of helium ions and helium plasma with the following parameters: power density qe = 5 × 108 W/cm2 for electrons; qipl = 1 × 108 W/cm2 for ion-plasma flow; pulse duration τe = 20 ns and τipl = 50 ns, respectively; and the number of pulsed impacts N = 15. It is shown that, in the implemented irradiation mode, the melting of tungsten surface layer by ion-plasma flows occurs over the entire irradiation area and is noticeably stronger than by electron beams, the impact of which leads to very weak melting of individual local areas of the surface, which are island-like in character. After ion-plasma impact on the tungsten single crystal, a wavelike surface relief is formed, which contains blisters with undestroyed shell domes, microcracks located in mutually perpendicular directions, and pores. In the irradiated surface layer of tungsten, a transformation of the initial monocrystalline structure into a polycrystalline cellular structure is also observed. In the case of exposure of the tungsten single crystal to electron beams, two mechanisms of structural changes in the surface layer are established. One of them is related to the processes of melting and crystallization of the irradiated surface layer, which occur in its individual local areas and contribute to the formation of pores and microcracks. The second one is due to the solid-phase recrystallization process occurring as a result of thermal heating of a near surface layer deeper than the thickness of the melt, which is related to the release of energy during the scattering of the electron flow in the material. Under the influence of the resulting thermal stresses, a network of microcracks appears over the entire area of electron impact located along the slip lines of the crystallographic planes of the tungsten single crystal. The observed increased cracking of the surface layer of the studied tungsten single crystal contributes to the intensification of its erosion by sputtering and evaporation of the material under conditions of multiple radiation-thermal exposures.