X-ray backlighting density measurements of tungsten and aluminum wire and wire array z-pinches
Calibrated density measurements in both the coronal plasmas and dense cores of exploding W wire and wire array Z-pinches, powered by the {approximately}450 kA, 100 ns XP-pulser at Cornell University, have been made using two-frame x-ray backlighting in conjunction with known thickness W step wedges. The backlighting images are made by Mo wire X-pinch radiation filtered by 12.5 {micro}m Ti impinging upon a sandwich of films (Micrat VR, Kodak GWL, Kodak DEF) which have different sensitivities to increase the dynamic range of the method. A W step wedge filter is placed in front of the films, giving absolute line density calibration of each exposure with estimated errors ranging from 20 to 50%. Assuming x-ray absorption by the W plasma is the same as for the solid material, the authors are able to measure W areal densities from 3.2 x 10{sup 19} to 2 x 10{sup 17}/cm{sup 2}. These can be converted to number density assuming azimuthal symmetry. For example, for an exploded 7.5 {micro}m wire with a 15--20 {micro}m diameter dense core and a 1 mm corona diameter, the implied W volume density ranges from 2x10{sup 18} to over 10{sup 22}/cm{sup 3}. Integration of the line density gives an estimate of the fraction of the wire mass in the corona and core. For example, with 100 kA peak current in a single 7.5 {micro}m W wire, {approximately}70% (>90%) of the W mass is in the corona after 53 ns (61 ns). The authors also observe that the corona has large, roughly axisymmetric axial nonuniformity both in radius and in mass density. In addition, the coronal plasma contains more of the W mass, expands faster and is more uniform when the wire is surface-cleaned by preheating. In arrays of 2--8 wires with the same 100 kA total current, detectable coronal plasma appears after 25--35 ns, and much of it is swept toward the center of the array, forming a dense channel. The portion of the initial wire mass in the coronal plasma increases with smaller wire diameter and decreases with greater wire number: 15% for 4 x 13.5 {micro}m, 35% for 4 x 7.5 {micro}m, and 25% for 8 x 7.5 {micro}m, at 46--48 ns (unheated). Similar measurements are now being made with Al wires and an Al step wedge. Results will be presented.
- Research Organization:
- Cornell Univ., Ithaca, NY (US)
- Sponsoring Organization:
- Sandia National Laboratories
- OSTI ID:
- 20050988
- Resource Relation:
- Conference: 1999 IEEE International Conference on Plasma Science, Monterey, CA (US), 06/20/1999--06/24/1999; Other Information: PBD: 1999; Related Information: In: The 26th IEEE international conference on plasma science, 342 pages.
- Country of Publication:
- United States
- Language:
- English
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