Evidence and mechanisms of axial-radiation asymmetry in dynamic hohlraums driven by wire-array Z pinches
- Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
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 peak 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.
- OSTI ID:
- 20698343
- Journal Information:
- Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 2 Vol. 12; ISSN PHPAEN; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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