Interaction of a laser-produced copper plasma jet with ambient plastic plasma

Abstract

This work is aimed at the investigation of mutual interaction of plastic (CH) and copper axially symmetric plasmas, and the dependence on the ratio of their ablated masses. For that purpose we irradiated a plastic target with a Cu cylindrical insert of diameter 400 µm with a laser beam of radius exceeding that of the insert. In such an arrangement we were able to control the volumes and masses of interacting CH and Cu plasmas by varying the laser beam diameter. The experiment was carried out at the Prague Asterix Laser System (PALS) iodine laser. The laser provided a 250 ps pulse with an energy of 130 J at the third harmonic frequency (i.e. a wavelength of λ3 = 0.438 µm). The interaction of the laser-driven plasma jet with ambient plasma was studied by means of a three-frame interferometric system and a four-frame x-ray pinhole camera. For simulation of the experiment we used the two-dimensional hydrodynamic code ATLANT-HE. The reported results demonstrated that there is an optimal ratio of Cu and plastic plasma masses, at which stable extended Cu plasma jets can be created. Even a relatively thin plastic plasma envelope can compress the Cu plasma and control the jet formation. Thicker plastic plasma layers, however, lead to complex hydrodynamic motion accompanied by generation of transverse shock waves, which can completely suppress the jet formation. The pressure of the plastic plasma was found to be 1.35 times higher than that of the copper plasma. A theoretical analysis of the experimental results allows us to conclude that this difference in pressures follows from the essential differences in expansion dynamics of plasmas with low and high atomic numbers.