The effect of an axial magnetic field Bz on an imploding metallic gas-puff Z-pinch was studied using 2D time-gated visible self-emission imaging. Experiments were performed on the IMRI-5 generator (450 kA, 450 ns). The ambient field Bz was varied from 0.15 to 1.35 T. It was found that the initial density profile of a metallic gas-puff Z-pinch can be approximated by a power law. Time-gated images showed that the magneto-Rayleigh–Taylor instabilities were suppressed during the run-in phase both without axial magnetic field and with axial magnetic field. Helical instability structures were detected during the stagnation phase for Bz < 1.1 T. For Bz = 1.35 T, the pinch plasma boundary was observed to be stable in both run-in and stagnation phases. When a magnetic field of 0.3 T was applied to the pinch, the soft x-ray energy was about twice that generated without axial magnetic field, mostly due to longer dwell time at stagnation.

At present Z-pinch has evolved into a powerful plasma source of soft x-ray. This paper considers the energy balance in a radiating metallic gas-puff Z pinch. In this type of Z pinch, a power-law density distribution is realized, promoting suppression of Rayleigh-Taylor (RT) instabilities that occur in the pinch plasma during compression. The energy coupled into the pinch plasma, is determined as the difference between the total energy delivered to the load from the generator and the magnetic energy of the load inductance. A calibrated voltage divider and a Rogowski coil were used to determine the coupled energy and the load inductance. Time-gated optical imaging of the pinch plasma showed its stable compression up to the stagnation phase. The pinch implosion was simulated using a 1D two-temperature radiative magnetohydrodynamic code. Comparison of the experimental and simulation results has shown that the simulation adequately describes the pinch dynamics for conditions in which RT instability is suppressed. It has been found that the proportion of the Ohmic heating in the energy balance of a Z pinch with suppressed RT instability is determined by Spitzer resistance and makes no more than ten percent.

Filamentation is a type of magnetohydrodynamic instability that may develop in a currentcarrying plasma. It is supposed that filaments, individual current channels, are formed due to thermal instabilities. The growth of these instabilities is determined by the behavior of the electrical conductivity of the material depending on its thermodynamic parameters. If the conductivity increases with temperature, as is the case in a plasma, thermal instabilities should give rise to the formation of separate current channels. This paper presents an analysis of the development of thermal instabilities in imploding plasma liners performed in terms of small perturbation theory. The theoretical predictions are compared with the results of experiments conducted on the IMRI-5 facility at a current of amplitude up to 450 kA and rise time about 500 ns.

This paper presents the results of measuring the velocity of the plasma boundary during the compression of a metallic gas-puff Z pinch in an axial magnetic field. The experiment was conducted on the IMRI-5 facility (current pulse of 450-kA amplitude with a 450-ns rise time); the initial magnetic field Bz0 was varied in the range of 0.15–0.6 T. To measure the compression velocity, B-dot probes were used successfully. The data obtained with the B-dot probes agree with the results obtained by other methods [visible imaging and determination of the pinch radius as a function of the time-varying pinch inductance L(t)]. It is shown that the plasma compression velocity is (1–1.5) × 107 cm/s at Bz0 = 0 and 0.6 × 107 cm/s at Bz0 = 0.6 T.

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