Capillary discharge $Z$ pinches have been shown to be efficient drivers for x-ray lasers (XRLs). In this work we examine the possibility of realizing a ${\mathrm{H}}_{\alpha }$ nitrogen recombination laser ($3\to 2$ transition) at $\lambda =13.4\mathrm{nm}$, using a capillary discharge $Z$ pinch. A pulsed power generator with $60\mathrm{kA}$ peak current and $70\mathrm{ns}$ quarter period have been used to generate $Z$-pinch plasma in a $90\text{−}\mathrm{mm}$-long and $5\text{−}\mathrm{mm}$-diameter capillary. The plasma conditions were evaluated experimentally, using a filtered x-ray diode detector and time-integrated spectroscopy. The conditions required for the XRL were analytically estimated based on simple steady-state rate equations and then compared to experimental results. We demonstrated above 10% ${\mathrm{N}}^{7+}$ abundance at pinch time, while at least 50% is required. Then, in the expansion phase, the plasma is cooled in a time less than $5\mathrm{ns}$ to temperatures below $60\mathrm{eV}$, as needed for the recombination laser. These results suggest that the required conditions for nitrogen-recombination lasing could be achieved in a capillary discharge $Z$ pinch, but a higher-power driver might be needed.

• Received 22 April 2008

DOI:https://doi.org/10.1103/PhysRevE.78.056404