Capillary discharge soft X-ray lasing in Ne-like Ar pumped by long current pulses

A capillary discharge soft X-ray laser operating at 46.9 nm on the transition $3p{-}3s$ ($J = 0{-}1$) of the Ne-like Ar has been realized by exciting the active medium with a long half-cycle duration current pulse of 140 ns. The current is produced by discharging a 10 nF water dielectric capacitor, initially charged to voltages lower than 200 kV by a six stage Marx generator, through a 15-cm long capillary channels. The laser amplification has been obtained by properly adjusting all the other experimental parameters. Utilizing a 3-mm in diameter Al2O3 capillary channel initially filled with 0.3 torr of Ar pressure, a laser beam, which has a 4-mrad divergence and a time duration of 1.3 ns, is characterized by a gain of $0.6\pm0.1$ cm-1. The stability of the plasma compression followed by the laser emission is verified