The results of an experimental study of the formation of micropinches (MP) in a plasma focus discharge in the presence of small impurities of heavy gas are reported. MPS of 10-100 mu m in size are observed and the X-ray spectra of multicharged ions of the impurity (Xe) are registered.

The aim of this study is to reproduce a superalfvenic collisionless shock wave by using the Plasma Focus Facility as a plasma source. The experiments were performed on PF-3 Facility (Plasma Focus Filippov-type) at the level of energy supply up to 1 MJ. At compression of a current-plasma sheet to an axis in the stage of a plasma focus formation, the generation of cumulative plasma jets driven along the axis with a velocity ∼ 10 7 cm/s takes place. This directed driving is realized in the ambient plasma arisen as a result of the working gas ionization by the X-ray radiation of the plasma focus. The transversal magnetic field up to 2500 G was created by the magnetic system based on rare-earth magnets. The experimental conditions allowed us to perform experiments with Alfvén Mach number MA≥3.

Experiments on zeta-pinches have shown that the surface layer of the plasma can be ejected towards the walls of the chamber. Phenomena of this type usually develop when the discharge current flowing through the circuit is decreasing, but they can also occur with a rising current when there is recurring discharge ignition.The application of an axial-magnetic field does not prevent the surface layer of the plasma from being ejected towards the chamber walls; it merely limits the rate at which the process occurs.It is shown that the break-up of the plasma sheath is due mainly to a reverse current induced in the surface layer of the pinch. When the discharge current is decreasing, a reverse current is produced by the 'inverse skin effect' [1].It is suggested that plasma losses due to the 'inverse skin effect' may also be observed for certain discharge regimes in theta-pinch, zeta, Tokamak and other systems.

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A compact and simple type of current driver based on a plasma focus working in the mode of a plasma opening switch was used for excitation of a capillary discharge in Ar pressures in the range 0.1-0.5 Torr. A current of up to 50-60 kA with a rise time of about 200 ns was achieved in the capillary. The Ar plasma was compressed from an initial diameter of 5 mm to a diameter of 1 mm. The dynamics of compression have been studied using time-resolved VUV pin-hole diagnostics. Time-resolved VUV spectra show that the plasma consists mainly of the Ne- and F-like ions Ar IX and Ar X. A spectral line at 468.7 Å, which was identified as the transition in Ne-like Ar IX, has an anomalously high intensity compared with other 3-3 transitions of Ar IX.