Soldered contact and current risetime effects on negative polarity wire array Z pinches
The experimental results described in this paper were motivated by earlier, low current, single wire experiments. In these experiments, single 10 – 25 μ m diameter wires were driven by 1–5 kA current pulses with variable d I / d t from 5 to 60 A/ns. The amount of energy deposited in the wires, the...
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Veröffentlicht in: | Physics of plasmas 2009-08, Vol.16 (8), p.082707-082707-9 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The experimental results described in this paper were motivated by earlier, low current, single wire experiments. In these experiments, single
10
–
25
μ
m
diameter wires were driven by 1–5 kA current pulses with variable
d
I
/
d
t
from 5 to 60 A/ns. The amount of energy deposited in the wires, the expansion rate, and expansion uniformity that occurred before a plasma induced voltage collapse were found to depend on the polarity,
d
I
/
d
t
, and the quality of the contacts between the wires and the electrodes. This paper reports the results of experiments with cylindrical wire arrays driven by Cornell Beam Research Accelerator (COBRA) [J. B. Greenly, J. D. Douglas, D. A. Hammer
et al.
, Rev. Sci. Instrum.
79, 073501 (2008)] current pulses that reached 1 MA. The pulse lengths were varied from 100 to 200 ns. These larger current pulses drove the wires of the array through the initiation phase studied in the single wire experiments and through ablation and Z-pinch implosion to stagnation on the cylindrical axis of the array. Regardless of the current pulse length, the COBRA
d
I
/
d
t
per wire during initiation reached approximately 175 A/ns and resistive voltage breakdown occurred at
∼
13
ns
. Wire-electrode contacts were modified by soldering the cathode ends of the wires to the brass electrode. With the 100 ns COBRA pulse, voltage monitor data suggested that soldering produced a smaller radius pinch, but bolometer data showed that this did not affect the total energy emitted from the array compared to nonsoldered contacts. With the 200 ns COBRA pulse and soldered contacts, the bolometer data showed an average of 69% increase in time integrated x-ray emission and the photoconducting detector data showed an increase in x-ray power and yield compared with nonsoldered contacts. Under these same conditions the four-frame extreme ultraviolet images showed a more pronounced “Christmas tree” effect at the cathode. |
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ISSN: | 1070-664X 1089-7674 |
DOI: | 10.1063/1.3212590 |