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Title: Wire Initiation Critical for Radiation Symmetry in Z-Pinch-Driven Dynamic Hohlraums

Abstract

Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor.

Authors:
; ; ; ; ; ; ; ; ;  [1]; ;  [2];  [3]; ;  [4];  [5]
  1. Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
  2. Ktech Corporation, Albuquerque, New Mexico 87123 (United States)
  3. Institute of Theoretical and Experimental Physics, Moscow 117218 (Russian Federation)
  4. Imperial College, London SW7 2BW (United Kingdom)
  5. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
Publication Date:
OSTI Identifier:
20955451
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 98; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevLett.98.065003; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AXIAL SYMMETRY; ELECTRIC FIELDS; INERTIAL CONFINEMENT; LINEAR Z PINCH DEVICES; WIRES; X RADIATION

Citation Formats

Sanford, T. W. L., Jennings, C. A., Rochau, G. A., Rosenthal, S. E., Stygar, W. A., Bennett, L. F., Bliss, D. E., Cuneo, M. E., Leeper, R. J., Nash, T. J., Sarkisov, G. S., Mock, R. C., Sasorov, P. V., Chittenden, J. P., Haines, M. G., and Peterson, D. L. Wire Initiation Critical for Radiation Symmetry in Z-Pinch-Driven Dynamic Hohlraums. United States: N. p., 2007. Web. doi:10.1103/PHYSREVLETT.98.065003.
Sanford, T. W. L., Jennings, C. A., Rochau, G. A., Rosenthal, S. E., Stygar, W. A., Bennett, L. F., Bliss, D. E., Cuneo, M. E., Leeper, R. J., Nash, T. J., Sarkisov, G. S., Mock, R. C., Sasorov, P. V., Chittenden, J. P., Haines, M. G., & Peterson, D. L. Wire Initiation Critical for Radiation Symmetry in Z-Pinch-Driven Dynamic Hohlraums. United States. doi:10.1103/PHYSREVLETT.98.065003.
Sanford, T. W. L., Jennings, C. A., Rochau, G. A., Rosenthal, S. E., Stygar, W. A., Bennett, L. F., Bliss, D. E., Cuneo, M. E., Leeper, R. J., Nash, T. J., Sarkisov, G. S., Mock, R. C., Sasorov, P. V., Chittenden, J. P., Haines, M. G., and Peterson, D. L. Fri . "Wire Initiation Critical for Radiation Symmetry in Z-Pinch-Driven Dynamic Hohlraums". United States. doi:10.1103/PHYSREVLETT.98.065003.
@article{osti_20955451,
title = {Wire Initiation Critical for Radiation Symmetry in Z-Pinch-Driven Dynamic Hohlraums},
author = {Sanford, T. W. L. and Jennings, C. A. and Rochau, G. A. and Rosenthal, S. E. and Stygar, W. A. and Bennett, L. F. and Bliss, D. E. and Cuneo, M. E. and Leeper, R. J. and Nash, T. J. and Sarkisov, G. S. and Mock, R. C. and Sasorov, P. V. and Chittenden, J. P. and Haines, M. G. and Peterson, D. L.},
abstractNote = {Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor.},
doi = {10.1103/PHYSREVLETT.98.065003},
journal = {Physical Review Letters},
number = 6,
volume = 98,
place = {United States},
year = {Fri Feb 09 00:00:00 EST 2007},
month = {Fri Feb 09 00:00:00 EST 2007}
}
  • Abstract not provided.
  • No abstract prepared.
  • Dynamic hohlraums driven by arrays consisting of large numbers of tungsten wires in Z pinches exhibit differences in radiation emitted from REHs (radiation exit holes) symmetrically located at either end of the hohlraum [Sanford et al., Phys. Plasmas 10, 1187 (2003)]. Significantly greater peak power is radiated from the top (anode) REH relative to the bottom (cathode) REH. Spectral measurements of tungsten M-shell emission (2-2.4 keV) indicate the peak radiated power from either REH anticorrelates with the fraction of wire-array tungsten plasma inferred to sweep across (or into the field of view of) the REH near the time of peakmore » axial emission. In all cases, greater M-shell emission relative to the total emission in the band 1.4-4 keV is measured at the bottom REH in comparison to the top REH. The decrease in peak power radiated from the bottom REH relative to the top appears to be due, in part, to an increase in localized opacity arising from the presence of increased wire-array tungsten plasma near the bottom REH. The asymmetry in both peak axial power and pulse shape is largely removed by adding two thin annular pedestals extending 3 mm into the anode-cathode gap from either electrode, just radially outboard of the REHs. The pedestals are designed to prevent the radial flow of tungsten plasma from prematurely crossing the REHs. A polarity effect [Sarkisov et al., Phys. Rev. E 66, 046413(6) (2002)] during wire initiation may offer one possible explanation for the underlying cause of such a tungsten-related axial power asymmetry.« less
  • Over the last several years, rapid progress has been made evaluating the double-z-pinch indirect-drive, inertial confinement fusion (ICF) high-yield target concept (Hammer et al 1999 Phys. Plasmas 6 2129). We have demonstrated efficient coupling of radiation from two wire-array-driven primary hohlraums to a secondary hohlraum that is large enough to drive a high yield ICF capsule. The secondary hohlraum is irradiated from two sides by z-pinches to produce low odd-mode radiation asymmetry. This double-pinch source is driven from a single electrical power feed (Cuneo et al 2002 Phys. Rev. Lett. 88 215004) on the 20 MA Z accelerator. The doublemore » z-pinch has imploded ICF capsules with even-mode radiation symmetry of 3.1 {+-} 1.4% and to high capsule radial convergence ratios of 14-21 (Bennett et al 2002 Phys. Rev. Lett. 89 245002; Bennett et al 2003 Phys. Plasmas 10 3717; Vesey et al 2003 Phys. Plasmas 10 1854). Advances in wire-array physics at 20 MA are improving our understanding of z-pinch power scaling with increasing drive current. Techniques for shaping the z-pinch radiation pulse necessary for low adiabat capsule compression have also been demonstrated.« less
  • The axial radiation developed primarily from the interior of an imploding dynamic hohlraum (DH) target within a Z pinch using a single array with a large number of tungsten wires is compared with that generated using a standard [Phys. Plasmas 9, 3573 (2002)] nested (outer plus inner) array on Z. These measurements indicate that a single-array with a mass (2.5 mg) near that of the combined mass of the nested-array maximizes the DH axial power. At this mass, the DH utilizing the standard nested array generates (23±15)%(23±15)% more axial power than that of a single array. Measurements over a rangemore » of single-array masses (2–6 mg) show a decrease in radiation power for masses above 3.5 mg. Two-dimensional radiation magnetohydrodynamic simulations, which have successfully described radial emission from targetless implosions for both single and nested-array configurations [Phys. Plasmas 6, 2178 (1999)], but, do not follow the observed trends well. Furthermore, this lack of tracking implies that current 2D models, which take into account the development of the magnetic Rayleigh–Taylor (RT) instability in the r–zr–z plane, require improvements in order to provide a self-consistent description of the implosion dynamics and radiation production for DH experiments.« less