Spectroscopic studies of plasma streams generated in a 1-MJ plasma-focus facility with and without gas-puffing

The main aim of the reported experimental session was to study operational characteristics of a modified PF-1000U facility during a free propagation of a plasma-stream and its interactions with a carbon-fiber composite (CFC) target. The facility was equipped with an axial fast-acting valve for additional gas puffing into a region close to the electrodes outlets. Experiments were carried out with and without the gas puffing in chosen instants before the application of high voltage pulse. The operational regimes of the facility were established by changing these parameters and the initial charging voltage. To record optical spectra of the plasma radiation the use was made of a Mechelle 900 spectrometer coupled with a CCD-camera sensitive in a wavelength range of 300...1100 nm. During all reported experiments the exposition time was equal to 100 ns, but a time delay was changed to obtain data for different discharge phases. The performed spectral measurements enabled to study plasma dynamics, to identify plasma impurities, and to estimate electron densities and temperatures. The electron density in a free-propagating plasma stream was calculated from a linear Stark-effect observed for the D_α spectral line