Time-resolved grating spectroscopy of a N capillary discharge plasma for a recombination pumped x-ray laser

Capillary discharge plasmas can serve for recombination-pumped x-ray lasers. We present time-resolved x-ray spectra and density measurements of a nitrogen capillary discharge z-pinch plasma. We use a free-standing transmission grating spectrometer and a gated MCP camera. This is the first time both K-shell and L-shell line emission of the nitrogen plasma are recorded simultaneously. Comparison of the spectra with a 4-ion collisional-radiative atomic model, which accounts for opacity effects, shows that the plasma reaches a maximum temperature of kT_e=75-85eV during the pinch, and adiabatically cools in less than 4ns. This is slightly less than the newly estimated goal temperature of 110eV. The fast cooling demonstrates the feasibility of a recombination-scheme laser in the nitrogen Hα line at 13.37nm, if higher plasma temperature is achieved.