Features of Niobium Damage by Pulsed Laser Radiation in Comparison with Beam-Plasma Impact

摘要

Abstract The features of damageability of niobium by pulsed fluxes of laser radiation (LR) in free-running (power density qFR = 105–106 W/cm2 with pulse duration τFR = 700 μs) and Q-switched (q = 108–109 W/cm2, τQS = 80 ns) modes in comparison with pulsed effects of helium ion (HI) and helium plasma (HP) fluxes in the Plasma Focus (PF) setup at a flux power density qi ~ 108 W/cm2 and qp ~ 107 W/cm2, respectively, and pulse durations τi ≈ 30–50 ns and τp ≈ 100 ns were studied. LR fluxes were exposed to Nb in air; the working gas in the PF chamber was helium. It is shown that, in contrast to the effect of helium ion and helium plasma fluxes on niobium in the PF installation, which contribute to the erosion of the material, irradiation of niobium with pulsed LR in air fluxes under the implemented conditions does not cause noticeable surface erosion. When Nb is exposed to pulsed LR in the FR mode, the melt interacts with air and forms a thin film of elements of liquid and gas phases on the irradiated surface. A similar nature of Nb damageability under conditions of laser and beam-plasma treatment was found: a wavy relief of the irradiated surface with the presence of droplike fragments on it, extended wave crests, and microcracks. Irradiation of Nb with pulsed LR fluxes in the FR mode leads to formation of sections with block and cellular structures in the surface layer (SL), which are also formed after experiments in the PF chamber. It was found that, after laser treatment in the FR and Q-switched modes, bubbles (blisters) are not formed in the SL of niobium, which are always present on the irradiated surface when exposed to pulsed fluxes of HI and HP in the PF chamber owing to implantation of helium ions into Nb. It is noted that, in laser experiments, there is no possibility of implanting working gas ions into the material, which is typical of beam-plasma impacts in PF devices, which affects damageability parameters and modification of the structure of the irradiated SL.