On the effects of different regimes of plasma pulses affecting the material due to their succession

Highlight• The succession of pulses impacts the development of damages inside the sample. • Powerful pulses at the beginning of the irradiation cycle deteriorate the sample more. • Conductivity suggests the scope of damages extends further than other methods indicate. The tungsten (>99.97% W) samples were irradiated on plasma focus device (PF-12), with deuterium (D) as a working gas, in Tallinn University in Estonia. Two of the samples serve as references, being irradiated in only one regime (either in harsh regime with heat flux factor ∼1000 MW s^1/2 m² for plasma and ∼1.5• 10⁵ MW s^1/2 m² for fast ions, or in the mild regime with heat flux factor ∼40–45 MW s^1/2 m² for plasma and ∼2000 MW s^1/2 m² for fast ions). Three of the samples received 27 pulses combining the two aforementioned regimes. The combined effects are obtained by using two different plasma flux values and also by varying the timing when the harsh regime is implemented during the irradiation cycle of each sample. The research is conducted by analyzing the SEM images of the damaged surfaces, measuring the electrical conductivity of the material in the bulk, studying the SEM images and micro-hardness of sample's cross-sections. This will enable to draw conclusions on the range of damages due to the varied succession of used regimes. The results are then combined to estimate the applicability of conductivity measurements instead of using destructive invasive measuring methods (i.e., measurement of micro-hardness and SEM imaging of cross sections). The aims of our research is to shed some light on (1) whether and how the succession of different series of irradiations with varying power flux densities affects the formation of damages on and within the samples and (2) estimating the three-dimensional damages that are created within the bulk of material due to high-temperature plasma and ion shockwaves. Our study indicates that the damage in bulk is related to the timing of harsh regime plasma pulses. The use of measurements of conductivity enables to estimate the future development of the damages in bulk of the material.