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We describe a simple practical numerical method for simulating plasma driven within a vacuum chamber by a pulsed power generator. Typically, in this type of simulation, the vacuum region adjacent to the plasma is approximated as a highly resistive, light fluid; this involves computationally expensive solvers describing the diffusion of the magnetic field through this fluid. Instead, we provide a recipe for coupling pulsed power generators to the magnetohydrodynamics (MHD) domain by approximating the perfectly insulating vacuum as a light, perfectly conducting, inviscid MHD fluid and discuss the applicability of this counter-intuitive technique. This much more affordable ideal MHD representation is particularly useful in situations where a plasma exhibits interesting three-dimensional phenomena, either due to the design of the experiment or due to developing instabilities. We verified that this coupling recipe works by modeling an exactly solvable flux compression generator as well as a self-similar Noh-like solution and demonstrated convergence to the theoretical solution. We also showed examples of simulating complex three-dimensional pulsed power devices with this technique. We release our code implementation to the public (see https://github.com/beresnyak/verif_coupling). [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the thermal dissociation of PH[sub3] and NH[sub3] injected through a tantalum-based high-pressure gas-injection cell. Pyrolytic behavior of PH[sub3] and NH[sub3]; Description of the beam-flux patterns of PH[sub3] and NH[sub3]; Determination of the substitutional nitrogen species.

Presents information on a study which analyzed the defect-related spectral features of the near-band-edge luminescence from gallium arsenide (GaAs) grown by molecular beam epitaxy. Results of the hydrogen passivation performed; Measurement of residual acceptor impurities, shallow defects and the overall quality of the layers, with low temperature photoluminescence; Discussion of the growth conditions and electrical properties of the GaAs samples.

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. [ABSTRACT FROM AUTHOR]

The distribution of argon gas injected by a 12-cm-diameter triple-shell nozzle was characterized using both planar, laser-induced fluorescence (PLIF) and high-sensitivity interferometry. PLIF is used to measure the density distribution at a given time by detecting fluorescence from an acetone tracer added to the gas. Interferometry involves making time-dependent, line-integrated gas density measurements at a series of chordal locations that are then Abel inverted to obtain the gas density distribution. Measurements were made on nominally identical nozzles later used for gas-puff Z-pinch experiments on the Saturn pulsed-power generator. Significant differences in the mass distributions obtained by the two techniques are presented and discussed, along with the strengths and weaknesses of each method. [ABSTRACT FROM AUTHOR]

A holographic interferometer is used to determine the radial electron number density profile of a sheared-flow Z pinch. Chord-integrated density information is recorded during a plasma pulse using the expanded beam of a pulsed ruby laser and holographic techniques. An Interactive Data Language (IDL) computer routine that requires only minimal user interaction is used to measure the resulting fringe shift in the reconstructed interferogram. This chord-integrated density information is inverted using an Abel inversion to determine the radial electron density profile. The density profiles obtained show a radially symmetric plasma column with an electron density of 1016–1017 cm-3 above the background plasma density. Holographic measurements are made at different times on separate plasma pulses to track the evolution of the density profile over time. These measurements are corroborated by time-dependent measurements made using a He–Ne interferometer. [ABSTRACT FROM AUTHOR]

The stabilizing effect of a sheared axial flow on the m = 1 kink instability in Z pinches has been studied numerically with a linearized ideal magnetohydrodynamic model to reveal that a sheared axial flow stabilizes the kink mode when the shear exceeds a threshold. The sheared flow stabilizing effect is investigated with the ZaP (Z-Pinch) Flow Z-pinch experiment at the University of Washington. An axially flowing Z pinch is generated with a 1 m coaxial accelerator coupled to a pinch assembly chamber. The plasma assembles into a pinch 50 cm long with a radius of approximately 1 cm. An azimuthal array of surface mounted magnetic probes located at the midplane of the pinch measures the fluctuation levels of the azimuthal modes m = 1, 2, and 3. After the pinch assembles a quiescent period is found where the mode activity is significantly reduced. Optical images from a fast framing camera and a ruby holographic interferometer indicate a stable, discrete pinch plasma during this time. Multichord Doppler shift measurements of impurity lines show a large, sheared flow during the quiescent period and low, uniform flow profiles during periods of high mode activity. Z-pinch plasmas have been produced that are globally stable for over 700 times the theoretically predicted growth time for the kink mode of a static Z pinch. The plasma has a sheared axial flow that exceeds the theoretical threshold for stability during the quiescent period and is lower than the threshold during periods of high mode activity. [ABSTRACT FROM AUTHOR]

Lattice-matched InGaAs/InP quantum well intersubband photodetectors (QWIPs) have been grown on an InP substrate by gas source molecular beam epitaxy. Detection at 4.55 μm was observed for a narrow well p-type InGaAs QWIP which, when complimented by a high responsivity 8.93 μm n-type InGaAs/InP QWIP, demonstrates the possibility of dual band, monolithically integrated QWIPs on the same InP substrate. Theoretical calculations of the photocurrent spectra are in excellent agreement with the experimental data. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Plasma density gradients are known to drive magnetic shocks in electron-magnetohydrodynamics. Previous slab modeling has been extended to cylindrical modeling of radially imploding shocks. The main new effect of the cylindrical geometry is found to be a radial dependence in the speed of shock propagation. This is shown here analytically and in numerical simulations. Ion acceleration by the magnetic shock is shown to possibly become substantial, especially in the peaked structures that develop in the shock because of electron inertia. [ABSTRACT FROM AUTHOR]