Browsing by Author "Beg, F. N."

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    MA-class linear transformer driver for Z-pinch research
    (2020) Conti, F.; Valenzuela Ahumada, Julio César; Fadeev, V.; Aybar, N.; Reisman, D. B.; Williams, A.; Collins, G.; Narkis, J.; Ross, M. P.; Beg, F. N.; Spielman, R. B.
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    Study of stability in a liner-on-target gas puff Z-pinch as a function of pre-embedded axial magnetic field
    (2020) Conti, F.; Aybar, N.; Narkis, J.; Valenzuela, J. C.; Rahman, H. U.; Ruskov, E.; Dutra, E.; Haque, S.; Covington, A.; Beg, F. N.
    Gas puff Z-pinches are intense sources of X-rays and neutrons but are highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI). MRTI mitigation is critical for optimal and reproducible yields, motivating significant attention toward various potential mitigation mechanisms. One such approach is the external application of an axial magnetic field, which will be discussed here in the context of recent experiments on the Zebra generator (1 MA, 100ns) at the University of Nevada, Reno. In these experiments, an annular Kr gas liner is imploded onto an on-axis deuterium target with a pre-embedded axial magnetic field Bz 0 ranging from 0 to 0.3T. The effect of Bz0 on the stability of the Kr liner is evaluated with measurements of plasma radius, overall instability amplitude, and dominant instability wavelength at different times obtained from time-gated extreme ultraviolet pinhole images. It was observed that the external axial magnetic field does not affect the implosion velocity significantly and that it reduces the overall instability amplitude and the presence of short-wavelength modes, indicating improved pinch stability and reproducibility. For the highest applied Bz0=0.3 T, the stagnation radius measured via visible streak images was found to increase. These findings are consistent with experiments reported in the literature, but here, the Bz0 required for stability, Bz0=0.13Ipk/R0 (where I-pk is the driver peak current and R-0 is the initial radius), is lower. This could be attributed to the smaller load geometry, both radially and axially. Consistent with other experiments, the cause of decreased convergence cannot be explained by the additional axial magnetic pressure and remains an open question. (C) 2020 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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    Talbot-Lau x-ray deflectometer: Refraction-based HEDP imaging diagnostic
    (AIP Publishing, 2021) Valdivia, M. P.; Stutman, D.; Stoeckl, C.; Theobald, W.; Collins, G. W.; Bouffetier, V; Vescovi, M.; Mileham, C.; Begishev, I. A.; Klein, S. R.; Melean, R.; Muller, S.; Zou, J.; Veloso, F.; Casner, A.; Beg, F. N.; Regan, S. P.
    C Talbot-Lau x-ray interferometry has been implemented to map electron density gradients in High Energy Density Physics (HEDP) experiments. X-ray backlighter targets have been evaluated for Talbot-Lau X-ray Deflectometry (TXD). Cu foils, wires, and sphere targets have been irradiated by 10-150 J, 8-30 ps laser pulses, while two pulsed-power generators (similar to 350 kA, 350 ns and similar to 200 kA, 150 ns) have driven Cu wire, hybrid, and laser-cut x-pinches. A plasma ablation front generated by the Omega EP laser was imaged for the first time through TXD for densities >10(23) cm(-3). Backlighter optimization in combination with x-ray CCD, image plates, and x-ray film has been assessed in terms of spatial resolution and interferometer contrast for accurate plasma characterization through TXD in pulsed-power and high-intensity laser environments. The results obtained thus far demonstrate the potential of TXD as a powerful diagnostic for HEDP. Published under an exclusive license by AIP Publishing.