Capillary Z-pinches with low currents and voltages for soft X-ray Ar+8 laser excitation

The 46.9-nm $\mathrm{Ar}^{+8}$ laser with capillary Z-pinch excitation is usually excited by high-current ($10-80 \mathrm{kA}$) pulses produced by a peaking water capacitor (5 nF) charged by a high-voltage ($U=0.2-0.8 \mathrm{MV}$) Marx generator. Our goal is to develop compact pumping systems with low current ($I\lt20 \mathrm{kA}$) and voltage ($U\lt$ 200 kV) to excite $\mathrm{Ar}^{+8}$ lasers without the use of water capacitors. We employed three alternative excitation techniques to demonstrate Z pinches suitable for excitation of the $46-\mathrm{nm} \mathrm{Ar}{ }^{+8}$ laser. The first approach employs a Marx bank ($U=180 \mathrm{kV}$) that is discharged directly through an argon-filled capillary. The second method is based on the generation of Z pinches with a fast impulse transformer $(U=90 \mathrm{kV})$ that does not use a peaking capacitor. The third approach employs a thyratron-driven L-C inversion circuit similar to that used in standard TEA XeCl-excimer lasers, but with the addition of magnetic switch compressor technology. Using the first and second laser excitation systems, the 46.9-nm lasing was achieved with an output energy of up to $\sim 0.5 \mu \mathrm{J}$. In the third system, the $45-\mathrm{kV} \mathrm{Z}$ pinches generated 46.9 -nm laser pulses with an energy of $3 \mu \mathrm{J}$ and a beam divergence of 2 mrad. The optimization of excitation systems for increasing laser energy is discussed. The $\mathrm{Ar}^{+8}$ lasers were also studied theoretically. The properties of laser-plasma channels were investigated using a one-fluid, two-temperature, and one-dimensional magneto-hydrodynamic model, an atomic kinetic code, and a ray tracing code for various pumping scheme parameters.