Surface Structure Transformation in Double Forged Tungsten upon Single and Sequenced Irradiation Using Different Types of Radiation Facilities

Structural changes in the surface layer of target samples made of double forged tungsten were investigated after successive pulsed plasma irradiation thereof using different irradiation facilities such as plasma focus (PF), plasma gun (PG), and plasma accelerator (PA). The irradiation modes simulated hard conditions occurring under the action of thermonuclear plasma on the material in modern tokamaks in such extreme situations as plasma disruption, vertical displacement, and edge localized mode effects (ELMs). Hydrogen and deuterium were used as working gases. Double forged tungsten (DFW) samples were irradiated using PF facilities (PF-6 and PF-1000U) with a subsequent irradiation using PG or PA, as well as another sequence consisting in the initial irradiation using PA and a subsequent irradiation using PF-6 at the final stage. The DFW samples in the experiments were positioned normal to the incident energy flux. The following irradiation modes were used. The PF-1000U facility provides a power density of the deuterium plasma flux onto the target surface qpl = 109–1010 W/cm2, pulse duration τpl = 50–100 ns, power density of the of fast ion beam (with energy Ei > 100 keV) qfi = 1011–1012 W/cm2, pulse duration τfi = 10–50 ns. The PF-6 facility provides qpl = 109–1010 W/cm2, τpl = 50 ns, qfi = 1010–1011 W/cm2, τfi = 10–50 ns. The PG facility provides energy density Q = 0.8 MJ/m2, density of hydrogen plasma q ≈ 5 × 106 W/cm2, pulse duration τ = 15 μs. The PA facility provides Q = 0.75 MJ/m2, power density of deuterium plasma q = 3.6 × 105 W/cm2, τ = 0.25 ms. General features and peculiarities inherent in tungsten damage and changes in the structural state thereof under the action of energy flows in the hard mode of preliminary irradiation in PF facilities with subsequent radiation exposure in softer modes implemented in PG and PA facilities are considered. It is shown that, in the irradiation modes under investigation, the character of material degradation depends not only on the magnitude and duration of the single energy pulses generated by a testing facility but also on the number of energy pulses. The depth of the apparent damaged layer, wherein the crippling of the material occurs, is about 200 μm in almost all the studied irradiation modes, the damage being of thermal and shock-wave nature.