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Fundamental science investigations to develop a 6-MV laser triggered gas switch for ZR: first annual report

Maenchen, John E.; Savage, Mark E.; Struve, Kenneth W.; Woodworth, Joseph R.; Lehr, J.M.; Warne, Larry K.; Bliss, David E.; Jorgenson, Roy E.; LeChien, Keith R.; McKee, George R.; Pasik, Michael F.; Rosenthal, Stephen E.

In October 2005, an intensive three-year Laser Triggered Gas Switch (LTGS) development program was initiated to investigate and solve observed performance and reliability issues with the LTGS for ZR. The approach taken has been one of mission-focused research: to revisit and reassess the design, to establish a fundamental understanding of LTGS operation and failure modes, and to test evolving operational hypotheses. This effort is aimed toward deploying an initial switch for ZR in 2007, on supporting rolling upgrades to ZR as the technology can be developed, and to prepare with scientific understanding for the even higher voltage switches anticipated needed for future high-yield accelerators. The ZR LTGS was identified as a potential area of concern quite early, but since initial assessments performed on a simplified Switch Test Bed (STB) at 5 MV showed 300-shot lifetimes on multiple switch builds, this component was judged acceptable. When the Z{sub 20} engineering module was brought online in October 2003 frequent flashovers of the plastic switch envelope were observed at the increased stresses required to compensate for the programmatically increased ZR load inductance. As of October 2006, there have been 1423 Z{sub 20} shots assessing a variety of LTGS designs. Numerous incremental and fundamental switch design modifications have been investigated. As we continue to investigate the LTGS, the basic science of plastic surface tracking, laser triggering, cascade breakdown, and optics degradation remain high-priority mission-focused research topics. Significant progress has been made and, while the switch does not yet achieve design requirements, we are on the path to develop successively better switches for rolling upgrade improvements to ZR. This report summarizes the work performed in FY 2006 by the large team. A high-level summary is followed by detailed individual topical reports.

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TYPE SAND Report YEAR 2007
OSTIDOI

Wire initiation critical for radiation symmetry in Z-pinch-driven dynamic hohlraums

Physical Review Letters

Sanford, T.W.L.; Jennings, C.A.; Rochau, G.A.; Rosenthal, Stephen E.; Sarkisov, G.S.; Sasorov, P.V.; Stygar, William A.; Bennett, Lawrence F.; Bliss, David E.; Chittenden, J.P.; Cuneo, M.E.; Haines, M.G.; Leeper, Ramon J.; Mock, R.C.; Nash, Thomas J.; Peterson, D.L.

Axial symmetry in x-ray radiation of wire-array z pinches is important for the creation of dynamic hohlraums used to compress inertial-confinement-fusion capsules. We present the first evidence that this symmetry is directly correlated with the magnitude of the negative radial electric field along the wire surface. This field (in turn) is inferred to control the initial energy deposition into the wire cores, as well as any current shorting to the return conductor. © 2007 The American Physical Society.

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TYPE Conference YEAR 2007
ScopusOSTI

Progress in symmetric ICF capsule implosions and wire-array z-pinch source physics for double z-pinch driven hohlraums

Proposed for publication in Plasma Physics and Controlled Fusion.

Cuneo, M.E.; Nash, Thomas J.; Yu, Edmund Y.; Mehlhorn, Thomas A.; Matzen, M.K.; Vesey, Roger A.; Bennett, Guy R.; Sinars, Daniel S.; Stygar, William A.; Rambo, Patrick K.; Smith, Ian C.; Bliss, David E.

Over the last several years, rapid progress has been made evaluating the double-z-pinch indirect-drive, inertial confinement fusion (ICF) high-yield target concept (Hammer et al 1999 Phys. Plasmas 6 2129). We have demonstrated efficient coupling of radiation from two wire-array-driven primary hohlraums to a secondary hohlraum that is large enough to drive a high yield ICF capsule. The secondary hohlraum is irradiated from two sides by z-pinches to produce low odd-mode radiation asymmetry. This double-pinch source is driven from a single electrical power feed (Cuneo et al 2002 Phys. Rev. Lett. 88 215004) on the 20 MA Z accelerator. The double z-pinch has imploded ICF capsules with even-mode radiation symmetry of 3.1 {+-} 1.4% and to high capsule radial convergence ratios of 14-21 (Bennett et al 2002 Phys. Rev. Lett. 89 245002; Bennett et al 2003 Phys. Plasmas 10 3717; Vesey et al 2003 Phys. Plasmas 10 1854). Advances in wire-array physics at 20 MA are improving our understanding of z-pinch power scaling with increasing drive current. Techniques for shaping the z-pinch radiation pulse necessary for low adiabat capsule compression have also been demonstrated.

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TYPE Journal Article YEAR 2005
OSTI

Shockless magnetic acceleration of al flyer plates to ultra-high velocity using multi-megabar drive pressures

Lemke, Raymond W.; Knudson, Marcus D.; Davis, Jean-Paul D.; Bliss, David E.; Slutz, Stephen A.; Giunta, Anthony A.; Harjes, Henry C.

The intense magnetic field generated in the 20 MA Z-machine is used to accelerate metallic flyer plates to high velocity for the purpose of generating strong shocks in equation of state experiments. We present results pertaining to experiments in which a 0.085 cm thick Al flyer plate is magnetically accelerated across a vacuum gap into a quartz target. Peak magnetic drive pressures up to 4.9 Mbar were produced, which yielded a record 34 km/s flyer velocity without destroying it by shock formation or Joule heating. Two-dimensional MHD simulation was used to optimize the magnetic drive pressure on the flyer surface, shape the current pulse to accelerate the flyer without shock formation (i.e., quasi-isentropically), and predict the flyer velocity. Shock pressures up to 11.5 Mbar were produced in quartz. Accurate measurements of the shock velocity indicate that a fraction of the flyer is at solid density when it arrives at the target. Comparison of measurements and simulation results yields a consistent picture of the flyer state at impact with the quartz target.

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TYPE Conference YEAR 2005
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Results 76–100 of 120
Results 76–100 of 120