Parallel and sequential tests of radiation resistance of double forged tungsten in various plasma devices

Identical tungsten specimens perspective for their use in modern nuclear fusion reactors have been tested under powerful plasma streams and beams of fast ions in various radiation devices (plasma accelerator, plasma gun and dense plasma foci) in wide ranges of radiation pulse durations (from ∼ 10 −8 s to ∼ 10 −4 s), power flux densities of the above streams (from ∼ 10 6 W/cm 2 to ∼ 10 12 W/cm 2 ), plasma densities (from 10 15 cm −3 to ∼ 10 19 cm −3 ), temperatures (from ∼ few eV to 1 keV) and fast ions energies (from ∼ 10 keV to ∼ a few MeV). Metallographic indexes of damageability examined in irradiated samples of tungsten demonstrate in our case that in the conditions of high-energy action with the damage factor similar to those in the regimes of disruption instability, VDE and ELMs effects in tokamaks the nature (character) of the material's degradation is practically the same in all cases and it does not depend on a source of energy load and a type of plasma used (hydrogen, deuterium). Within the interval of the high power flux densities used in present researches with Dense Plasma Foci (q ∼ 10 9 –10 12 W/cm 2 ) the damage character depends not only and not so much from the energy of single pulses produced by an irradiation facility as from the number of pulses retransmitted to the material. Depth of noticeable damage of a layer where the breakdown of the material's integrity takes place is equal to 200 μm and more. The nature of the damage is of the shock-wave and fatigue-thermal character. In the layer the discontinuity flaws (micro-cracks including V-shaped ones) appear and spread as in parallel to the irradiated surface so at an angle to it — very likely along the borders of blocks. An increase of the number of irradiation pulses results in spalling of material from the surface in early stages and in intermixing of material at prolonged (∼1000 shots) irradiation campaign. Recrystallization processes manifest themselves faintly and they occupy a very thin sub-layer of melting and multiple re-melting appeared at the prolonged tests and large number of pulses. Depending on the irradiation conditions this formed and crystalized thin (of the order of a few μm) sub-layer contains a net of micro-cracks, spool-like figures of crystallization, and tungsten droplets. Character of the surface after multiple cycles of irradiation may be changed by height from the “flat” ridge-wave shape to the large-scale pot-hole one.