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

A recombination based X-Ray laser has a preferred energy scaling compared to collisional ionization scheme [1-3]. The difficulty in realizing this scheme lies in the required plasma cooling rate [4,5]. Implementing a nitrogen recombination laser at $\lambda \sim $13.4 nm, requires initially T$_{e}\sim $140eV and N$_{e}\sim $10$^{20}$cm$^{-3}$, and than cooling to T$_{e}<$60eV, at a time scale shorter than the 3-body recombination time scale of 3-6ns. An experimental setup has been built to achieve these conditions in a capillary discharge. A 90mm long capillary with 3-6mm inner diameter was filled with 0.5-3 Torr N$_{2}$ and coupled to a generator supplying a peak current of 60-70 KA at 70 ns. The radiation from N$^{5+}$ and N$^{6+}$ was measured with XRD and appropriate filters. The results show that the cooling time of the plasma is shorter than 5 ns, indicationg that the recombination scheme may be feasible. The experimental measurements will be used in search for the optimal initial conditions for lasing. \newline [1] Elton R. C.: \textit{X-Ray Lasers}, Academic Press, New York, 1990. \newline [2] Rocca J.J. \textit{et. al}., \textbf{PRL 73}, 2192, (1994). \newline [3] Ben-Kish A. \textit{et. al.}, \textbf{PRL} \textbf{87}, 015002, (2001) \newline [4] Lee K., Kim J. H., Kim D., \textbf{Phys. of plasmas} \textbf{9}, 4749, (2002). \newline [5] Vrba P., \textit{et. al.}\textbf{, 6th Intl. Conf. on Dense Z-Pinches}, 2005