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Astrophysical jets with conical wire arrays: Radiative cooling, rotation & deflection

AIP Conference Proceedings

Ampleford, David A.; Lebedev, S.V.; Ciardi, A.; Bland, S.N.; Hall, G.N.; Bott, S.C.; Suzuki-Vidal, F.; Palmer, J.B.A.; Jennings, C.A.; Chittenden, J.P.

Highly collimated outflows or jets are produced by a number of astrophysical objects including protostars. The morphology and collimation of these jets is thought to be strongly influenced by the effects of radiative cooling, angular momentum and the interstellar medium surrounding the jet. Astrophysically relevant experiments are performed with conical wire array z-pinches investigating each of these effects. It is possible in each case to enter the appropriate parameter regime, leading the way towards future experiments where these different techniques can be more fully combined. © 2009 American Institute of Physics.

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TYPE Conference YEAR 2009
ScopusOSTIDOI

2D radiation MHD K-shell modeling of single wire array stainless steel experiments on the Z machine

AIP Conference Proceedings

Thornhill, J.W.; Giuliani, J.L.; Apruzese, J.P.; Chong, Y.K.; Davis, J.; Dasgupta, A.; Whitney, K.G.; Clark, R.W.; Jones, Brent M.; Coverdale, Christine A.; Ampleford, David A.; Cuneo, M.E.; Deeney, C.

Many physical effects can produce unstable plasma behavior that affect K-shell emission from arrays. Such effects include: asymmetry in the initial density profile, asymmetry in power flow, thermal conduction at the boundaries, and non-uniform wire ablation. Here we consider how asymmetry in the radiation field also contributes to the generation of multidimensional plasma behavior that affects K-shell power and yield. To model this radiation asymmetry, we have incorporated into the MACH2 r-z MHD code a self-consistent calculation of the non-LTE population kinetics based on radiation transport using multi-dimensional ray tracing. Such methodology is necessary for modeling the enhanced radiative cooling that occurs at the anode and cathode ends of the pinch during the run-in phase of the implosion. This enhanced radiative cooling is due to reduced optical depth at these locations producing an asymmetric flow of radiative energy that leads to substantial disruption of large initial diameter (>5 cm) pinches and drives ID into 2D fluid (i.e., Rayleigh-Taylor like) flows. The impact of this 2D behavior on K-shell power and yield is investigated by comparing ID and 2D model results with data obtained from a series of single wire array stainless steel experiments performed on the Z generator. © 2009 American Institute of Physics.

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TYPE Conference YEAR 2009
ScopusOSTI

Generation of shear flow in conical wire arrays with a center wire

Astrophysics and Space Science

Ampleford, David A.

At the Nevada Terawatt Facility we investigated the generation of a sheared plasma flow using conical wire arrays with an additional wire located on the axis of the pinch. The additional center wire generates axial current carrying plasma that serves as a target for the plasma accelerated from the outer wires, generating a sheared plasma flow which leads to the growth of the Kelvin-Helmholtz instability. These experiments were conducted on Zebra, a 2 TW pulse power device capable of delivering a 1 MA current in 100 ns. This paper will focus on the implosion dynamics that lead to shear flow and the development of the Kelvin Helmholtz instability.

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TYPE Journal Article YEAR 2008
OSTI

Compact wire array sources: power scaling and implosion physics

Jones, Brent M.; Cuneo, M.E.; Ampleford, David A.; Coverdale, Christine A.; Vesey, Roger A.; Jones, Michael J.

A series of ten shots were performed on the Saturn generator in short pulse mode in order to study planar and small-diameter cylindrical tungsten wire arrays at {approx}5 MA current levels and 50-60 ns implosion times as candidates for compact z-pinch radiation sources. A new vacuum hohlraum configuration has been proposed in which multiple z pinches are driven in parallel by a pulsed power generator. Each pinch resides in a separate return current cage, serving also as a primary hohlraum. A collection of such radiation sources surround a compact secondary hohlraum, which may potentially provide an attractive Planckian radiation source or house an inertial confinement fusion fuel capsule. Prior to studying this concept experimentally or numerically, advanced compact wire array loads must be developed and their scaling behavior understood. The 2008 Saturn planar array experiments extend the data set presented in Ref. [1], which studied planar arrays at {approx}3 MA, 100 ns in Saturn long pulse mode. Planar wire array power and yield scaling studies now include current levels directly applicable to multi-pinch experiments that could be performed on the 25 MA Z machine. A maximum total x-ray power of 15 TW (250 kJ in the main pulse, 330 kJ total yield) was observed with a 12-mm-wide planar array at 5.3 MA, 52 ns. The full data set indicates power scaling that is sub-quadratic with load current, while total and main pulse yields are closer to quadratic; these trends are similar to observations of compact cylindrical tungsten arrays on Z. We continue the investigation of energy coupling in these short pulse Saturn experiments using zero-dimensional-type implosion modeling and pinhole imaging, indicating 16 cm/?s implosion velocity in a 12-mm-wide array. The same phenomena of significant trailing mass and evidence for resistive heating are observed at 5 MA as at 3 MA. 17 kJ of Al K-shell radiation was obtained in one Al planar array fielded at 5.5 MA, 57 ns and we compare this to cylindrical array results in the context of a K-shell yield scaling model. We have also performed an initial study of compact 3 mm diameter cylindrical wire arrays, which are alternate candidates for a multi-pinch vacuum hohlraum concept. These massive 3.4 and 6 mg/cm loads may have been impacted by opacity, producing a maximum x-ray power of 7 TW at 4.5 MA, 45 ns. Future research directions in compact x-ray sources are discussed.

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TYPE SAND Report YEAR 2008
OSTIDOI

Bright spots in 1 MA X pinches as a function of wire number and material

Proposed for publication in Physics of Plasmas.

Ampleford, David A.; Cuneo, M.E.; Wenger, D.F.

Bright, intense x-ray sources with extreme plasma parameters (micropinch plasmas) have previously been characterized at 0.1-0.4 MA, but the scaling of such sources at higher current is poorly understood. The x-ray source size and radiation power of 1 MA X pinches were studied as a function of wire material (Al, Ti, Mo, and W) and number (1-, 2-, 8-, 32-, and 64-wire configurations). The smallest bright spots observed were from 32-wire tungsten X pinches, which produced {le} 11-16 {micro}m, {approx}2 J, 1-10 GW sources of 3-5 keV radiation.

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TYPE Journal Article YEAR 2008
OSTI

Planar wire array dynamics and radiation scaling at multi-MA levels on the Saturn pulsed power generator

Jones, Brent M.; Cuneo, M.E.; Ampleford, David A.; Coverdale, Christine A.; Vesey, Roger A.; Jones, Michael J.

Planar wire arrays are studied at 3-6 MA on the Saturn pulsed power generator as potential drivers of compact hohlraums for inertial confinement fusion studies. Comparison with zero-dimensional modeling suggests that there is significant trailing mass. The modeled energy coupled from the generator cannot generally explain the energy in the main x-ray pulse. Preliminary comparison at 1-6 MA indicates sub-quadratic scaling of x-ray power in a manner similar to compact cylindrical wire arrays. Time-resolved pinhole images are used to study the implosion dynamics.

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TYPE Conference YEAR 2008
OSTI

Astrophysical jets with conical wire arrays : radiative cooling, rotation & deflection

Ampleford, David A.; Jennings, Christopher A.

Highly collimated outflows or jets are produced by a number of astrophysical objects including protostars. The morphology and collimation of these jets is thought to be strongly influenced by the effects of radiative cooling, angular momentum and the interstellar medium surrounding the jet. Astrophysically relevant experiments are performed with conical wire array z-pinches investigating each of these effects. It is possible in each case to enter the appropriate parameter regime, leading the way towards future experiments where these different techniques can be more fully combined.

More Details
TYPE Conference YEAR 2008
OSTI
Results 226–250 of 273
Results 226–250 of 273