Implosions of NaF plasmas for photopumping a Na-Ne x-ray laser

Abstract

Intense heliumlike sodium 11-Å line radiation is required to resonantly photopump a neon plasma in the Na-Ne soft x-ray laser scheme. The implosion of a NaF capillary-discharge plasma with a 3-MA peak current is used to produce a power exceeding 100 GW in this Heα line. The power is optimized by varying both the initial radius of the 3-cm-long NaF plasma column and the time delay between the capillary current and the generator current. Maximum power of 115 GW is obtained for implosions which occur just after peak current. Burn-through of the heliumlike sodium stage is evident in spectroscopic measurements where sodium Lyα line emission is 2–4 times stronger than Heα emission. Mass loadings of 200–400 μg/cm are inferred from measured implosion times and initial plasma diameters. The nearly pure density dependence of the Heα power and the nearly pure temperature dependence of the Lyα/Heα ratio allow the state of the plasma to be determined by measuring both quantities on a single shot. For these implosions, electron temperatures are 350–560 eV and total ion densities approach 1020 cm−3. The mass load inferred from implosion dynamics is consistent with the ion density deduced from spectral measurements.