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James H Goforth,
Dennis H Herrera,
Douglas G Tasker,
David T Torres,
W. L. Atchison,
S. A. Colgate,
J. R. Griego,
J. Guzik, D. B. Holtkamp,
G. Idzorek, [......],
R. Menikoff,
R. K. Meyer,
H. Oona,
P. T. Reardon,
R. E. Reinovsky,
C. L. Rousculp,
A. G. Sgro,
L. J. Tabaka,
R. G. Watt,
D. B. Riesman
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ABSTRACT: In the late 1990s, Los Alamos pursued a coaxial flux compression generator (FCG) concept that was described in several publications under the name 'Ranchero.' These FCGs were designed to be cost effective high current generators, and a variety of configurations were tested. The Ranchero armature is a 152 mm diameter aluminum cylinder with a 6 mm thick wall. The high explosive (HE) is detonated simultaneously on axis, and as the armature expands a factor of two, the wall thins to {approx}3 mm. At the final 300 mm diameter, the circumference is over 900 mm, and this should allow currents to be generated in the 90 MA range. No tests significantly over 50 MA have been performed but an experiment is planned. We have recently begun using Ranchero devices for a new application and we continue to improve the design. In this paper we describe recent tests of Ranchero and its subsystems. The load for our new application is an imploding aluminum liner that would deform due to the magnetic pressure applied during the initial flux loading. It will, however, implode properly when powered only during the {approx}29 {micro}s Ranchero flux compression time. This gives rise to a new system with explOSively formed fuse (EFF) opening switches and an integral closing switch that isolates the load. A capacitor bank delivers 2.8 MA to the Ranchero circuit in {approx}85 {micro}s. During this time, four parallel 63.5 mm wide EFFs, external to the coaxial system, complete the circuit. After armature motion begins, insulation which initially isolates the load is severed, connecting the load to the FCG in parallel with the EFFs. External HE charges are initiated on each of the EFFs to produce a resistance rise timed to not precede closure of the load isolation switch. The EFFs achieve significant resistance, and the flux remaining in the 191 nH generator and 3 nH transmission line is compressed to generate 30.85 MA in a {approx}12.5 nH static load. On three tests, the EFF system has operated flawlessly, and only {approx}100kA is driven back into the EFFs during peak voltage of the generator output. A test incorporating a 19.5 nH dual liner dynamic load has also been completed, and these results are also presented. Ranchero generators have been operated with armatures from 43 cm to 1.4 m long, corresponding to initial inductances from 56 to 191 nH. MHD code modeling gives better agreement with experiments using modules 43 cm long than the 1.4 m modules, and these results will also be presented.
11/2010
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J.H. Goforth,
W.L. Atchison,
S.A. Colgate,
J.R. Griego,
J. Guzik,
D.H. Herrera, D.B. Holtkamp,
G. Kaul,
R.C. Kirkpatrick,
R. Menikoff,
R.K. Meyer,
H. Oona,
P.T. Reardon,
C. Reinovsky,
L. Rousculp,
A.G. Sgro,
L.J. Tabaka,
T.E. Tierney,
D.T. Torres,
R.G. Watt
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ABSTRACT: We are developing a new high explosive pulsed power (HEPP) system based on the 1.4 m long Ranchero generator which was developed in 1999 for driving solid density z-pinch loads. The new application requires approximately 40 MA to implode similar liners, but the liners cannot tolerate the 65 ¿s, 3 MA current pulse associated with delivering the initial magnetic flux to the 200 nH generator. To circumvent this problem, we have designed a system with an internal start switch and four explosively formed fuse (EFF) opening switches. The integral start switch is installed between the output glide plane and the armature. It functions in the same manner as a standard input crowbar switch when armature motion begins, but initially isolates the load. The circuit is completed during the flux loading phase using post hole convolutes. Each convolute attaches the inner (coaxial) output transmission line to the outside of the outer coax through a penetration of the outer coaxial line. The attachment is made with the conductor of an EFF at each location. The EFFs conduct 0.75 MA each, and are actuated just after the internal start switch connects to the load. EFFs operating at these parameters have been tested in the past. The post hole convolutes must withstand as much as 80 kV at peak dI/dt during the Ranchero load current pulse. We describe the design of this new HEPP system in detail, and give the experimental results available at conference time. In addition, we discuss the work we are doing to test the upper current limits of a single standard size Ranchero module. Calculations have suggested that the generator could function at up to ~120 MA, the rule of thumb we follow (1 MA/cm) suggests 90 MA, and simple flux compression calculations, along with the ~4 MA seed current available from our capacitor bank, suggests 118 MA is the currently available upper limit.
Pulsed Power Conference, 2009. PPC '09. IEEE; 08/2009
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A. Seifter,
M. R. Furlanetto,
M. Grover, D. B. Holtkamp,
G. S. Macrum,
A. W. Obst,
J. R. Payton,
J. B. Stone,
G. D. Stevens,
D. C. Swift,
L. J. Tabaka,
W. D. Turley,
L. R. Veeser
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ABSTRACT: Equilibrium equation of state theory predicts that the free-surface release temperature of shock-loaded tin will show a plateau at 505 K in the stress range from 19.5 to 33.0 GPa, corresponding to the solid-liquid, mixed-phase region of tin. In this paper we report free-surface temperature measurements on shock-loaded tin from 15 to 31 GPa using multiwavelength optical pyrometry. The shock waves were generated by direct contact of detonating high explosive with a tin sample, and the stress in the sample was determined by free-surface velocity measurements using photon Doppler velocimetry. We measured the emitted thermal radiance in the near IR region at four wavelengths from 1.5 to 5.0 μ m . Above 25 GPa the measured free-surface temperatures were higher than the predicted 505 K, and they increased with increasing stress. This deviation may be explained by hot spots and/or variations in surface emissivity, and it may indicate a weakness in the use of a simple analysis of multiwavelength pyrometry data for conditions, such as above the melt threshold, where hot spots or emissivity variations may be significant. We are continuing to study the discrepancy to determine its cause.
Journal of Applied Physics 07/2009; · 2.17 Impact Factor
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G. D. Stevens,
S. S. Lutz,
B. R. Marshall,
W. D. Turley,
L. R. Veeser,
M. R. Furlanetto,
R. S. Hixson, D. B. Holtkamp,
B. J. Jensen,
P. A. Rigg,
M. D. Wilke
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ABSTRACT: When highly polished metal surfaces melt upon release after shock loading, they exhibit features that suggest that significant surface changes accompany the phase transition. The reflection of light from such surfaces changes from specular (preshock) to diffuse upon melting. A familiar manifestation of this phenomenon is the loss of signal light observed with a velocity interferometer system for any reflector, which occurs at pressures high enough to melt the free surface. Unlike many other potential material phase-sensitive diagnostics (e.g., reflectometry and conductivity) that show relatively small changes, the specularity of reflection provides a more sensitive and definitive indication of the solid-liquid phase transition. Data are presented that support the hypothesis that specularity changes indicate melt in a way that can be measured easily and unambiguously.
Journal of Applied Physics 08/2008; · 2.17 Impact Factor
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ABSTRACT: Symmetric, plate-impact experiments were performed to validate photon Doppler velocimetry (PDV) with established shock wave diagnostics. Impact velocity measurements using shorting pins demonstrated that the velocity accuracy of PDV can be 0.1% or better. Shock velocities and refractive indices were also measured with PDV (at 1550 nm) and velocity interferometer system for any reflector (VISAR) (at 532 nm) to obtain window corrections for single crystal LiF (100), c-cut sapphire, and z-cut quartz. Time-dependent, free-surface velocity histories for shocked LiF(100) provide a direct comparison between PDV and VISAR diagnostics and illustrate the benefits and shortcomings of the new diagnostic. Further implications of these results are presented.
Journal of Applied Physics 01/2007; 101(1):013523-013523-10. · 2.17 Impact Factor
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D. Partouche-Sebban,
J. L. Pélissier,
F. G. Abeyta,
W. W. Anderson,
M. E. Byers,
D. Dennis-Koller,
J. S. Esparza,
R. S. Hixson, D. B. Holtkamp,
B. J. Jensen,
J. C. King,
P. A. Rigg,
P. Rodriguez,
D. L. Shampine,
J. B. Stone,
D. T. Westley,
S. D. Borror,
C. A. Kruschwitz
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ABSTRACT: Data on the high-pressure melting temperatures of metals is of great interest in several fields of physics including geophysics. Measuring melt curves is difficult but can be performed in static experiments (with laser-heated diamond-anvil cells, for instance) or dynamically (i.e., using shock experiments). However, at the present time, both experimental and theoretical results for the melt curve of lead are at too much variance to be considered definitive. As a result, we decided to perform a series of shock experiments designed to provide a measurement of the melt curve of lead up to about 50 GPa in pressure. At the same time, we developed and fielded a reflectivity diagnostic, and conducted measurements on tin as well. The results show that the melt curve of lead is somewhat higher than the one previously obtained with static compression and heating techniques.
Journal of Applied Physics 01/2005; 97(4):043521-043521-11. · 2.17 Impact Factor
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A. Seifter,
K. Boboridis,
D.A. Clark,
R.B. Corrow, D.B. Holtkamp,
C.W. McCluskey,
G.L. Morgan,
J.R. Payton,
P. Quintana,
C.E. Ragan,
P. Rodriguez,
H.L. Stacy,
W.S. Vogan,
V.W. Yuan,
A.W. Obst
9th International Symposium on Temperature and Thermal Measurements in Industry and Science (TEMPMEKO 2004), Cavtat - Dubrovnik, Croatia; 06/2004
