Spectroscopic study of rapid mixing and cooling of a high-density He plasma flow penetrating into hydrogen gas

Rapid mixing and cooling of a high-density helium plasma flow injected into hydrogen gas was experimentally confirmed for the first time, which is essentially of importance to generate a recombining plasma as a short-wavelength laser medium. The plasma flow was produced by a small Z-pinch gun. The electron temperature and density was spectroscopically measured to be 12 eV and 6×10 16 cm -3 , respectively, before injected into the hydrogen gas. After injection of the gas, the plasma was rapidly cooled down to 4 eV while the density increased only by about 30%. It was also found that the cooled plasma tended to a recombining phase. A simplified calculation was also performed on the collisional radiative model to show that the rapid cooling was due to the atomic collisions between the electrons and hydrogen atoms mixed with the plasma.