Radiation cooling of dense laboratory plasma jets studied using soft x-ray laser interferometry and simulations

The physical mechanisms responsible for the collimation of laboratory plasma jets created with short laser pulses of $\sim $0.5-1 J energy were studied using soft x-ray interferometry and hydrodynamic code simulations. Plasma jets with peak densities of $\sim $10$^{20 }$cm$^{-3}$ were created by irradiation of C, Al, Cu, and Mo 90\r{ } triangular grooved targets with I = 1 x 10$^{12}$ Wcm$^{-2}$, 120 ps duration laser pulses. Also, plasma jets with a much higher electron density, $>$10$^{21 }$cm$^{-3}$, were created by irradiation of Cu cone shaped targets with I = 3 x 10$^{13}$ Wcm$^{-2}$. The results were compared with simulations conducted with the code HYDRA. Plasma radiation cooling was found to play a significant role in increasing the collimation of the higher Z jets. In addition, at any instance in the evolution the higher Z jets appear to be more collimated due to their slower plasma expansion velocity associated with their higher mass. Work supported by the NNSA SSAA program through DOE Grant {\#} DE-FG52-060NA26152 and the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.