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Previous Staged Z-pinch experiments have demonstrated that gas liners (or puffs) can efficiently couple energy to a target plasma and implode uniformly, producing plasmas in High Energy Density (HED) regimes. In these experiments, a 50 kJ, 1.5 MA, 1 μs current driver was used to implode a magnetized, Kr liner onto a D+ target, producing 1010 neutrons per shot. Time-of-flight data suggested that primary and secondary neutrons were produced.

We discuss the design and characterization of a compact gas-puff nozzle and plasma gun assembly that will be used in Staged Z-pinch experiments1, where gas liners are imploded onto an on-axis target-plasma column. Previous work on the Staged Z-pinch demonstrated that gas liners can efficiently couple the energy and produce a uniform implosion on a target-plasma.2

The propagation of near-infrared ultra-short laser pulses in the regime of anomalous dispersion of transparent solids is associated with a host of self-induced effects including a significant spectral broadening extending from the ultraviolet into the infrared region, pulse self-compression down to few-cycle pulse durations, free and driven third harmonic generation, conical emission and the formation of stable filaments over several \(\mathop{\mathrm{cm}}\nolimits\) showing the emergence of conical light bullets. We review measurements performed in different experimental conditions and results of numerical simulations of unidirectional propagation models showing that the interpretation of all these phenomena proceeds from the formation of non-spreading conical light bullets during filamentation.

In preparation for measuring neutrons generated in experiments on the Zebra 1-MA Z-pinch generator at the Nevada Terawatt Facility, we use the Monte Carlo N-Particles (MCNP) radiation transport code to characterize neutron activation detectors. For reasonable assumptions regarding the emitted neutron pulse characteristics, the MCNP code is used to predict the expected neutron signal taking into account scattering events and thermalization effects from the neutron scatter. These effects can bolster neutron yield derivations via unique room geometries and, in general, higher absorption cross-section values for lower neutron energies. We report on neutron yield detector characterization, calibrated against NSTec's dense plasma focus for a known neutron yield, and the build-up factors calculated with MCNP necessary for a measurement of a correct neutron yield at NTF.

International audience; Filamentation in the anomalous dispersion regime is experimentally shown to give rise to an extreme blueshifted continuum peak in the visible region even when the filament is formed by near-infrared pulses. Measurements and numerical simulations allow us to identify this peak as an axial component of the conical emission. Its features are characterized and quantitatively reproduced by the effective three-wave mixing model.

Star wire arrays with two closely located wires (“gates”) on the inner cylinder of star wire arrays were studied. The gate wires were used to study plasma interpenetration and reproduce transparent and non-transparent regimes of propagation of the imploding plasma through the gates. The non-transparent mode of collision is typical for regular star wire arrays and it was also observed in Al stars with gate wires of regular length. Gated star arrays demonstrate similar x-ray yield but slightly different delay of x-ray generation compared to regular stars. Double length wires were applied as gate wires to increase their inductance and resistance and to increase transparency for the imploding plasma. The wires of the gates were made of Al or high atomic number elements, while the rest of the arrays were regular length Al wires. An intermediate semi-transparent mode of collision was observed in Al stars with long Al gate wires. Arrays with long heavy-element gate wires demonstrated transparency to plasma passing through. Shadowgraphy at the wavelength of 266 nm showed that plasma moved through the gate wires. Double implosions, generating a double-peak keV X-ray pulse, were observed in star arrays when the gates were made of high atomic number elements. A new laser diagnostic beampath for vertical probing of the Z-pinch was built to test how wires could be used to redirect plasma flow. This setup was designed to test gated arrays and further configurations to create a rotating pinch. Results on plasma flow control obtained are discussed, and compared to numerical calculations.

Laser probing diagnostics at the wavelength of 266 nm have been developed at the 1-MA pulsed power Zebra facility. Due to the smaller absorption and refraction at 266 nm, UV radiation penetrates deeper into the dense Z-pinch plasma. This allows the observation of fine details and structures of the Z-pinch plasma at the implosion and stagnation phases. UV interferograms and shadowgrams of the z-pinch plasma were compared to regular interferograms and shadowgrams at 532 nm. The UV laser shadowgraphy was shown to be a significant improvement in probing of wire array plasmas. Plasma distribution and dynamics in compact cylindrical, star, and planar wire arrays were studied at the wavelength of 266 nm. An electron density N e >5.1019 cm-3 was measured directly in the stagnated Z-pinch with the 266nm differential interferometer. Two-color shadowgraphy shows low density "corona" plasma with the 532 nm laser and dense plasma structures with the 266 nm laser in wire arrays.

The properties of a femtosecond laser filament (the initial collapse distance and plasma length) have been studied in a pre-aligned gas and prove to be an effective diagnostic for molecular alignment.