Soldered Contact and Current Risetime Effects on Negative Polarity Wire Array Z-pinches

Journal Article · Wed Jan 21 00:00:00 EST 2009 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3079745· OSTI ID:21255355

Chalenski, D A; Kusse, B R; Greenly, J B; Blesener, I C; McBride, R D; Hammer, D A; Knapp, P F ^[1]

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1. Cornell University Laboratory of Plasma Studies, 439 Rhodes Hall, Ithaca, NY 14853 (United States)

The Cornell University COBRA pulser is a nominal 1 MA machine, capable of driving up to 32 wire cylindrical Z-pinch arrays. COBRA can operate with variable current risetimes ranging from 100 ns to 200 ns (short and long pulse, respectively). Wires are typically strung with a 'press' contact to the electrode hardware, where the wire is loosely pulled against the hardware and held there to establish electrical contact. The machine is normally negative, but a bolt-on convolute can be used to modify the current path and effectively produce positive polarity operation at the load.Previous research with single wires on a 1-5 kA pulser has shown that soldering the wire, thereby improving the wire/electrode contact, and operating in positive polarity can improve the energy deposition into the wire and enhance wire core expansion. Negative polarity showed no difference. Previous experiments on the negative polarity, 20 MA, 100 ns Z accelerator have shown that improving the contact improved the x-ray yield.Cornell data were collected on 16-wire Aluminum Z-pinch arrays in negative polarity. Experiments were conducted with both short and long current pulses with soldered and no-soldered wire/electrode contacts. The initiation, ablation, implosion and stagnation phases were compared for these four conditions. Time dependent x-ray signals were measured using diodes and diamond detectors. An inductive voltage monitor was used to infer minimum current radius achieved, as defined by a uniform shell of current moving radially inward, producing a time dependent inductance. Total energy data were collected with a metal-strip bolometer. Self-emission data were collected by an XUV 4-frame camera and an optical streak camera.In negative polarity and with short pulses, soldering appeared to produce a smaller radius pinch and decrease variations in the x-ray pulse shape. The bolometer, laser backlighter, 4-frame and streak cameras showed negligible differences in the initiation ablation and implosion phases. X-ray yield was increased with soldered arrays in negative polarity with long pulses. The bolometer also showed a 50% increase in radial power emitted for soldered arrays. 4-frame images showed soldered arrays have a more pronounced 'Christmas Tree' effect originating from the cathode. The inductive voltage monitor showed, with both long and short pulses, that soldered and no-solder arrays reached the same minimum current radius at the same time. However, with long pulses soldered arrays radiate x-rays at the time of minimum current radius while no-solder array x-ray output is delayed by {approx}20 ns, resulting in decreased x-ray yield.

• OSTI ID: 21255355
• Journal Information: AIP Conference Proceedings, Vol. 1088, Issue 1; Conference: 7. international conference on dense Z-pinches, Alexandria, VA (United States), 12-21 Aug 2008; Other Information: DOI: 10.1063/1.3079745; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABLATION
ACCELERATORS
ALUMINIUM
BOLOMETERS
CYLINDRICAL CONFIGURATION
DIAMONDS
ELECTRIC CONTACTS
ELECTRIC POTENTIAL
EXPANSION
EXTREME ULTRAVIOLET RADIATION
IMPLOSIONS
LINEAR Z PINCH DEVICES
PLASMA HEATING
PULSE SHAPERS
PULSES
SOLDERING
STREAK CAMERAS
TIME DEPENDENCE
WIRES
X RADIATION