Pulsed capillary discharge with special shape of current in a large diameter tube

Recombination pumping of N⁶⁺ Balmer alpha line transition is effected by fast heating up to 140eV through high current Z-pinching plasma in capillary discharge and fast plasma cooling to less then 60eV by adiabating pinch expansion in the time slot of 5 ns. The evolution of a nitrogen plasma discharge in a tube with an inner diameter of 8 or 9.2 mm, excited by a particular pulse shape, was studied to suppress ablation from the inner wall. Ablated wall material is slowing-down the plasma cooling. Therefore excitation is realized by three current pulses. The first one is a long pre-ionization pulse, which guarantees the stability of the plasma column, the second one is a higher current pulse, which causes the detachment of the discharge plasma from the wall and its partial compression. The third is fast high current pulse which finally compress ionized column of plasma by Z-pinch. The evolution of plasma in the tube is modeled using the magneto-hydrodynamic code NPINCH and obtained results are used to calculate time dependence of gain at 13.4 nm wavelength by Flych. The results of simulations are showing and compared with measurement.