Nitrogen Recombination X-Ray Laser Scheme in a Capillary Discharge Z-Pinch

Summary form only given. A recombination based X-ray laser has a preferred energy scaling compared to the collisional ionization scheme. Implementing a nitrogen recombination laser at lambda~13.4 nm, requires a confined plasma initially at T_e~140 eV and N_e~10²⁰ cm^-3 to be rapidly cooled to T_e<60 eV. The cooling time scale should be shorter than the 3-body recombination time scale of 3-6 ns. The difficulty in realizing this scheme lies in the required plasma cooling rate. An experimental setup has been built to achieve these conditions in a capillary discharge. A 90 mm long capillary with a 3 to 6 mm inner diameter was filled with 0.5-2 torr N₂ and was coupled to a pulse power generator supplying a peak current of 60-70 kA at a rise time of 70 ns. The radiation from N⁶⁺ and N⁷⁺ ions was measured with an X-ray diode probe implementing appropriate filters. The results show that the cooling time of the plasma is shorter than 5 ns, indicating that the recombination scheme may be feasible. The experimental measurements will be used in search for the optimal initial conditions for lasing.