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Experimental Study of Merging Supersonic Plasma Jets Motivated by HEDLP and Plasma Science Applications

Author: Elizabeth C Merritt
Requested Type: Consider for Invited
Submitted: 2012-12-07 11:32:44

Co-authors: S. C. Hsu, A. L. Moser, S. Brockington, J. T. Cassibry, M. A. Gilmore, A. G. Lynn, and F. D. Witherspoon

Contact Info:
Los Alamos National Lab
Bikini Atoll Rd Sm-30
Los Alamos, NM   87545
USA

Abstract Text:
The Plasma Liner Experiment (PLX) at LANL recently completed experiments to characterize the propagation [1] and oblique merging of two supersonic argon plasma jets in order to assess the use of such jets for forming imploding spherical plasma liners [2,3,4], which are a proposed standoff driver for magneto-inertial fusion [5]. The plasma jets are formed and launched by pulsed-power-driven railguns built by HyperV Technologies Corp. Physics diagnostics include an eight-chord interferometer [6,7], a survey spectrometer and a fast framing camera. Electron density is measured both directly via the Stark-broadened H- line and also via interferometry. The spectral data are interpreted with the aid of non-LTE atomic/EOS modeling to infer Te and ionization fraction f. Initial jet parameters are ne21016 cm-3, Te1.4 eV, f0.96, velocity V30 km/s, sonic Mach number M14, diameter d5 cm, and length L20 cm. The average jet density decreases by a factor of ten over a propagation distance of 40 cm, which is at the very low end of the 8–160 times drop predicted by ideal hydrodynamic theory of a constant-M jet. The jet profiles were characterized by analyzing interferometer and CCD line-out data. In oblique merge experiments, we have experimentally identified (1) density increases that may be indicative of plasma compression and/or shock formation as opposed to simple plasma interpenetration, (2) no clear evidence yet of strong heating, and (3) the consistent formation of a multi-peaked emission structure (with scale length << c/pi) along the merge plane. Because the intra-jet collisionality is very high, but the counter-streaming ion collisionality is comparable to the merged-structure size, we interpret the observations using both hydrodynamic oblique shock and multi-fluid plasma theory and simulations. We close with brief discussions of the implications of these studies on plasma liner formation, and the status of ongoing work on experimental shock studies via the head-on merging of hydrogen plasma jets.

[1] S. C. Hsu et al., “Experimental characterization of railgun-driven supersonic plasma jets motivated by high energy density physics applications,” submitted for publication (2012); [2] T. J. Awe et al., Phys. Plasmas 18, 072705 (2011); [3] J. T. Cassibry et al., Phys. Plasmas 19, 052702 (2012); [4] J. S. Davis et al., Phys. Plasmas 19, 102701 (2012); [5] S. C. Hsu et al., IEEE Trans. Plasma Sci. 40, 1287 (2012); [6] E. C. Merritt et al., Rev. Sci. Instrum. 83, 033506 (2012); [7] E. C. Merritt et al., Rev. Sci. Instrum. 83, 10D532 (2012).

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