Morphological and structural effects on tungsten targets produced by fusion plasma pulses from a table top plasma focus

A table top plasma focus device operating at hundreds of joules was used to simulate an equivalent damage factor than the obtained on the divertor in tokamak experiments. Using the ejected plasma produced after the pinch disruptions, the effects on tungsten targets from 50 cumulative plasma shocks with power fluxes per shot between 2.6 and 9200 kW cm^-2 and with a duration time in the order of tens of nanoseconds (damage factor in the order of 10⁰-10³ (W cm^-2)s^1/2) were studied. Morphological analysis shows an increasing appearance of cracked surfaces with holes, fissures and defects, suggesting a potential progression of stress effects and a fast heat load that melts the surface, ending in thermal contractions that recrystallize the surface of the target. A structural analysis demonstrates a compressive stress development and suggests that part of the energy is released in the melting of the surface in case of a plasma shock with a power flux of 9.2 MW cm^-2, 75 ns duration pulse, 2.5   ×   10³ (W cm^-2)s^1/2 damage factor. How to increase the damage factor by one order of magnitude up to the expected value from type I ELMs on the ITER divertor, i.e. 10⁴ (W cm^-2)s^1/2 is discussed.