Influence of a Plasma Jet on Different Types of Tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10(22) m(-3) and 100-200 km/s, respectively, and the irradiation time is 10 mu s. Two plasma flux densities, 0.70 and 0.25 MJ/m(2), are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V_MP and ITER_D_2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V_MP powder samples, while the surface of the ITER_D_2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1-3 mu m, and the extension of intense thermal action is 15-20 mu m. The material acquires a distinct regular structure with a typical grain size of less than 1 mu m. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V_MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.