The acceleration of hydrogen ions up to 35 MeV is observed in the z-pinch experiments on the GIT-12 generator at a 3 MA current and 0.6 MV driving voltage. High ion energies are obtained with a novel configuration of a deuterium gas-puff z-pinch. In this configuration, a hollow cylindrical plasma shell is injected around an inner deuterium gas puff to form a homogeneous, uniformly conducting layer between electrodes at the initial phase of z-pinch implosion. The stable implosion at the velocity up to 650 km s −1 is important to deliver more current onto the z-pinch axis. Magnetohydrodynamic instabilities become apparent first at stagnation. After the disruptive development of m=0 instabilities, ∼20 ns pulses of high-energy photons, neutrons, electrons, and ions are observed. The average neutron yield is 2×10 12 . The ion emission is characterized by various diagnostic techniques including those based on the usage of neutronproducing samples. When a large neutron-producing sample is placed onto the axis below a cathode mesh, the neutron yield is increased up to (1.1±0.3)×10 13 . Considering a ∼130 kJ energy input into z-pinch plasmas and magnetic field, this implies the neutron production efficiency of ∼10 8 neutrons per one Joule of the z-pinch energy.

We describe a series of experiments performed to study the shock structure generated during the implosion of a gas-puff Z-pinch. The Z-pinch is produced by a double-annular gas-puff with a center jet driven by Cornell University's COBRA generator operating with a 1 MA, 200 ns current pulse. Using 532 nm laser interferometry and 100 MHz multi-frame cameras, a shock structure is observed to form early in the implosion. The shock appears to be created by a current layer at the outer radius of the imploding plasma which acts as a piston moving inward at several hundred km s−1. The dynamics of the shock and its radial position ahead of the piston agree well with a simple uniform density model outlined in the study by Potter [Nucl. Fusion 18(6), 813 (1978)]. The outer surface of the current layer is observed to be Magneto-Rayleigh-Taylor unstable. The growth rate of this instability is found to depend on the radial density profile of the material within the layer of high-density fluid between the shock and the piston, as predicted by recent theoretical work [see, e.g., D. Livescu, Phys. Fluids 16(1), 118 (2004)]. Growth rates measured in krypton implosions, where the post-shock material is found to decay quasi-exponentially away from the piston, were more than ten times smaller than those recorded in otherwise identical implosions in argon plasmas, where the material between the shock and the piston was observed to maintain a uniform density.

We have shown that the Zeeman splitting of the sodium (Na) D-lines at 5890 Å and 5896 Å can be used to measure the magnetic field produced by the current flowing in an exploding wire prior to wire explosion. After wire explosion, the lines in question are either not visible in the strong continuum from the exploding wire plasma, or too broad to measure the magnetic field by methods discussed in this paper. We have determined magnetic fields in the range 10-20 T, which lies between the small field and Paschen-Back regimes for the Na D-lines, over a period of about 70 ns on a 10 kA peak current machine. The Na source is evaporated drops of water with a 0.171 M NaCl solution deposited on the wire. The Na desorbs from the wire as it heats up, and the excited vapor atoms are seen in emission lines. The measured magnetic field, determined by the Zeeman splitting of these emission lines, estimates the average radial location of the emitting Na vapor as a function of time under the assumption the current flows only in the wire during the time of the measurement.

Z-pinch experiments with a hybrid configuration of a deuterium gas puff have been carried out on the HAWK (NRL, Washington, DC) and GIT-12 (IHCE, Tomsk) pulsed power generators at 0.7 MA and 3 MA currents, respectively. On GIT-12, neutron yields reached an average value of 2 × 1012 neutrons, and deuterons were accelerated up to an energy of 30 MeV. This was 50 times the ion energy provided by the generator driving voltage of 0.6 MV and the highest energy observed in z-pinches and dense plasma foci. To confirm these unique results independently on another device, we performed several experimental campaigns on the HAWK generator. Comparison of the experiments on GIT-12 and HAWK helped us to understand which parameters are essential for optimized neutron production. Since the HAWK generator is of a similar pulsed power architecture as GIT-12, the experiments on GIT-12 and HAWK are important for the study of how charged-particle acceleration scales with the current.

Voltage-current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltagecurrent characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2 / O2 with and without C4F7N or C5F10O additives at concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1 bar to 5 bar absolute, and electrode separations ranging from 20 mm to 95 mm. Voltagecurrent characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown, as well as fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage-current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high voltage peaks. The arc voltage in air had a similar minimum value to the CO2 based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.