XUV radiation from nitrogen filled capillary discharge plasma was diagnosed using a 104 grooves/mm SiNx free-standing
transmission grating. The resolution bandwidth of 0.3 nm was achieved. Time dependence of 13.4 nm line
emitted power was recorded by photomultiplier in order to verify inherence of resonant radiation emission corresponding
to NVII 2-3 laser transition. An increase of emitted power is expected during the pinch decay caused by recombination
processes. We report here results obtained with 90 mm long capillary discharge supplied by a current pulse with
maximum amplitude of 50kA and quarter-period of 80 ns. This high-current pulse was generated by a 1.5 ohm water line
high-voltage generator which is used for underwater wire explosion experiments and which was adjusted for capillary
discharge design using results of PSPICE simulations. Initial nitrogen pressures were varied in the range of 20 ÷ 500 Pa.
MHD and kinetic simulations of the discharge plasma were performed and compared with experimental data.
Simulations were performed with presumption of wall ablation. The capillary wall and electrodes material emission lines
were also identified in measured spectra.
We report new results of evaluated gain for 13.38 nm radiation created due to the inversion population on the Balmer
alpha transition of hydrogen-like nitrogen. Recombination pumping in non-equilibrium plasma during the capillary pinch
decay is judged. Quantitative analysis is performed in four-dimensional region of optional parameters chosen in
accordance with available experimental devices: current slope dI/dt|t=0 (0.9-3.0 1012 A/s), current peak value Imax (50-100 kA), capillary radius R0 (0.16-0.25 cm) and filling atom density N0 (1.0-6.0 1017 cm-3). Requirements on the current
pulse shape are stated. Diameter of the created active medium is estimated.
Pinching capillary discharge in nitrogen is investigated for the purpose of development of laser recombination pumping. An apparatus, previously realized for argon capillary laser pumping, was used to understand details of pinching mechanism and emission characteristics for capillary filled by nitrogen. Time dependences of radiation intensities emitted in the wavelength range 1.9 - 2.5 nm and time integrated in the spectral range 10 - 20 nm were measured under various pressures. A computer model is used to describe the pinch dynamics and to estimate the radiation characteristics. EUV reflection grating spectrometer coupled to BI CCD camera and filtered PIN diode were used for time integrated and time resolved spectral measurements respectively. The measured profiles of radiation intensities are compared with the computer simulations of time dependences of selected energy level populations that correspond to the hydrogen- and helium- like ion line emission in the detected spectral range. Complex method for spectral image restoration was developed.
The capillary experiment CAPEX was reconstructed to approach conditions suitable for creation of population inversion in Ne-like Ar. The reconstruction consisted in substitution of a ceramics capillary for former plastic one, in remarkable reduction of the pre-ionization current, and in change of Ar filling and pumping geometry. The soft X-ray spectroscopic measurements prior to and after this reconstruction are described. It is shown that the reconstruction resulted in appearance (under certain conditions) of the strong spectral line at the wavelength of laser transition (46.9 nm) that dominates the spectrum even at exposition 50 ns.
In this paper our new capillary discharge device built for the soft x-ray laser studies is described and the first experimental results obtained from electrical, optical and UV diagnostics together with code simulations are presented.
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