Deuterium gas puff experiments were carried out on the S-300 Z-pinch at the Kurchatov Institute in Moscow. Gas puffs imploded onto the axis before a current peak at about 100 ns. Fusion neutrons were generated after the gas puff implosion during global expansion of a plasma column. Neutron emission lasted on average 35 ± 5 ns (full width half maximum, FWHM). In the downstream direction (on the Z-pinch axis behind the cathode), a mean neutron energy was 2.6 ± 0.1 MeV. Side-on neutron energy spectra peaked at 2.40 ± 0.05 MeV with about 600 ± 150 keV FWHM. A broad width of sideon neutron spectra implied a high radial component of deuteron velocities. An average kinetic energy of fast deuterons, which produced fusion neutrons, was 150 keV. A peak neutron yield reached a value of 6 × 10 10 on a current level of 1.5 MA. It was by one order higher in comparison with other deuterated loads used on the same current generator. On the basis of experimental observations, we concluded that a total energy of deuterons accelerated to fusion energies was above 1.5 kJ. It is more than 15% of the energy input into a plasma. Therefore gas puff Z-pinches seem to be not only powerful sources of x-ray radiation but also efficient sources of 100 keV deuterons. Such a result is consistent with high Plasma Phys. Control. Fusion 52 (2010) 065013 D Klir et al neutron yields observed on the Angara Z-pinch and plasma foci with similar currents.

An optical system consisting of optical fibers and photodiodes arranged in four detection directions and in two planes perpendicular to the jet axis is used for the diagnostics of a thermal plasma jet where the application of one-directional observation is insufficient due to a strong disturbance of cylindrical symmetry. The experimental data are processed using the inverse Radon transform where the number of input profiles is extended by means of interpolation. The results show that the method application can bring new findings, e.g., in detection of coherent structures or evaluations of velocity distributions in thermal plasma jet under turbulent conditions.

Abstract:Temperatures in a thermal plasma jet were measured using an experimental set-up providing time-resolved scans of plasma optical radiation near 650 nm from 4 directions. The acquired data were used for reconstructions of time-resolved temperature distributions in measurement planes perpendicular to the plasma jet axis. The plasma torch was fed by the d.c. power source with a substantial ripple voltage modulation which leads to significant differences between the temperature distributions according to the actual phase of the arc current.Confidential: not for distribution.

The number, size, location and velocity of turbulent structures in an argon plasma jet were experimentally investigated using a fast-shutter CCD camera. The camera yielded sequences of plasma jet images with a time interval of 11 µs, and the turbulent structures in the jet were identified by subtraction of matrices representing the succeeding images in the series. This method reveals the regions characterized by increasing or decreasing luminosity that move along the plasma flow and reflect high energy and mass transport in these areas. The results show a high diversity of measured quantities characterizing these structures, and the evaluation thus required the involvement of statistical methods. The statistical distributions of the structure velocities change from non-Gaussian to Gaussian-like ones, depending on the gas flow rate, and so indicate the transitions from a turbulent flow characterized by a relatively regular structure generation to more developed turbulence.

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