S. A. Maslyaev

Generation of shock waves in materials science experiments with dense plasma focus device

The paper presents a comparison of the results of numerical simulations of the shock wave (SW) produced inside a stainless steel plate by a powerful pulsed stream of fast ions generated in a dense plasma focus device with its experimental observations. A SW was detected for the first time in a materials science experiment directly by means of multiframe nanosecond laser interferometry. This was visualized in experiments with the PF-1000 facility after the SW went out at the rear side of the thin stainless steel plate into the residual gas atmosphere. In particular, the pressure amplitude of the SW measured by the interferometric method was 16 GPa. The observed value is in good agreement with the results of numerical simulations of the SW pressure amplitude.

Armor materials’ behavior under repetitive dense plasma shots

Experiments on the plasma focus device PF-12 have been carried out to investigate changes in the structure of the surface and bulk of tungsten and tungsten doped with 1% lanthanum oxide after repeated powerful deuterium plasma shots (8, 25 and 100). The surface morphology of the targets exposed to plasma streams is analyzed by electron and optical microscopy. Due to the plasma effect, different surface structures, such as wave-like structures, a melted layer, a mesh of microcracks, droplets, craters, crevices and holes, appear. The change of cross-section hardness after a number of shots in different materials is investigated.

Features of the Damage and the Structural Changes in the Tungsten Surface Layer under the Pulsed Action of Laser Radiation,Ion and Plasma Fluxes

The degradation of a bilateral pressed tungsten surface layer by pulsed laser irradiation in the free-running mode (power density q = 105–5 × 106 W/cm2, pulse duration τ = 0.7 ms) and the Q-switched mode (q = 109–1010 W/cm2, τ = 80 ns) as well as under plasma beam irradiation in a plasma focus (PF) device (q = 108–1012 W/cm2, τ = 10–100 ns) has been investigated. The features of the degradation, erosion, and structural changes in the tungsten surface layer under different irradiation conditions have been determined. It has been shown that the use of PF devices in combination with laser equipment is promising for the simulation of the extreme radiation–thermal effects in materials that are typical of thermonuclear fusion devices with magnetic and inertial plasma confinement.

The Influence of a Powerful Stream of Deuterium Ions and Deuterium Plasma on the Structural State of the Surface Layer of Titanium

The effect of a high-power pulsed flow of deuterium ions and deuterium plasma generated in a plasma focus setup on the surface structure of a Ti plate was investigated. It was established that, depending on the radiation-thermal conditions on the surface, three zones with different surface morphology, structure, and defects were formed in the surface layer irradiated. The peculiarities of the surface damage in the center of the irradiated region of the Ti target exposed to the most severe radiation (power density of the ion and plasma flows of qi ≈ 1011–1012 and qp ≈ 109–1010 W/cm2, respectively) were studied, as well as those for the peripheral region exposed to softer radiation.

Athermal laser annealing of cold-worked aluminum

The influence of pulsed laser irradiation on mechanical properties of annealed and cold-worked pure aluminum is studied. Mechanical tests are performed by means of a miniaturized disk bend test technique using specimens with the diameter of 3 mm. It is established that laser irradiation does not influence the mechanical properties of annealed aluminum but leads to softening of cold-worked material. After 100 laser pulses, nearly complete recovery of aluminum strength occurs to the value characteristic of the annealed state. The plasticity of cold-worked aluminum is lower than that of annealed material and does not vary upon laser irradiation. Thermal and shock-wave mechanisms of laser impact are estimated, and it follows that, under the given parameters of irradiation, the main contribution to the variation of properties is that of shock-wave mechanism related to generation and propagation of acoustic waves which stimulate athermal annealing and recovery of dislocation structure.

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 ~ 106 W/cm2 to ~ 1012 W/cm2), plasma densities (from 1015 cm-3 to ~ 1019 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 materials 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 ~ 109-1012 W/cm2) 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 materials 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.