A large diameter gas puff nozzle, designed to produce a radial mass profile with a substantial fraction of the injected mass on the axis, has demonstrated an increase in K shell yield by nearly a factor of 2, to 21kJ, in an argon Z pinch at 3.5MA peak current and 205ns implosion time [H. Sze, J. Banister, B. H. Failor, J. S. Levine, N. Qi, A. L. Velikovich, J. Davis, D. Lojewski, and P. Sincerny, Phys. Rev. Lett. 95, 105001 (2005)] and 80kJ at 6MA and 227ns implosion time. The initial gas distribution produced by this nozzle has been determined and related to measured plasma dynamics during the implosion run-in phase. The role of two gas shells and the center jet are elucidated by the inclusion of a tracer element sequentially into each of the three independent plenums and by evacuating each plenum. The implosion dynamics and radiative characteristics of the Z pinches are presented.

We have developed a dual-plenum gas valve coupled to a double shell nozzle for the generation of “shell-on-shell” gas loads in z-pinch plasma radiation source experiments. The gas density profiles of the nozzles have been characterized with laser interferometry. This valve/nozzle combination has been successfully fielded on the Double-EAGLE and Saturn pulsed-power generators. The design and characterization of the shell-on-shell valve/nozzle are presented in this article.

A pinch-reflex ion diode is fielded on the pulsed-power machine Mercury (R. J. Allen, et al., 15th IEEE Intl. Pulsed Power Conf., Monterey, CA, 2005, p. 339), which has an inductive voltage adder (IVA) architecture and a magnetically insulated transmission line (MITL). Mercury is operated in positive polarity resulting in layered MITL flow as emitted electrons are born at a different potential in each of the adder cavities. The usual method for estimating the voltage by measuring the bound current in the cathode and anode of the MITL is not accurate with layered flow, and the interaction of the MITL flow with a pinched-beam ion diode load has not been studied previously. Other methods for determining the diode voltage are applied, ion diode performance is experimentally characterized and evaluated, and circuit and particle-in-cell (PIC) simulations are performed. Results indicate that the ion diode couples efficiently to the machine operating at a diode voltage of about 3.5 MV and a total current of about 325 kA, with an ion current of about 70 kA of which about 60 kA is proton current. It is also found that the layered flow impedance of the MITL is about half the vacuum impedance.

The Hawk pulsed power generator is used in plasma opening tch (POS) experiments in the 1-1s conduction time regime to study g conduction time switch physics. Experiments reported here lude modiflmg the POS electrode geometry, injecting plasma into e-beam diode, using gas gun plasma sources (with H2, He, and Ar ,es), and using a helical cathode center conductor in the switch ion to increase the total insulating magnetic field. Tapering the hode center conductor over the 8 cm POS length from 10 cm to, ically, a 2.5 cm diam produced peak load powers of 0.7 TW with kJ delivered to the diode--20% energy efficiency--with carbonrted flashboards as the plasma source. Performance (voltage, Mer generated) with a straight 10 cm diam cathode deteriorated en the POS anode outer conductor just downstream of the switch s extended toward the load at the same radius as the switch. Load Mer was up to 70% higher with a plasma-filled diode (PFD) used in ljunction with the POS for short POS conduction times (400 ns and j). Use of a helical center conductor resulted in dramatically;faded switch performance for >350 ns conduction times. Switch formance with gas guns was generally comparable to that with ihboards in a given switcMoad configuration and was independent ;he gas (H2, He, and Ar) used.

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