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The high current, fast, 100ns, Linear Transformer Driver (LTD) developmental project at Sandia National Laboratories

LeChien, Keith R.; Woodworth, Joseph R.; Fowler, William E.; Long, Finis W.; Matzen, M.K.; McDaniel, Dillon H.; McKee, George R.; Struve, Kenneth W.; Stygar, William A.

Sandia National Laboratories, Albuquerque, N.M., USA, in collaboration with the High Current Electronic Institute (HCEI), Tomsk, Russia, is developing a new paradigm in pulsed power technology: the Linear Transformer Driver (LTD) technology. This technological approach can provide very compact devices that can deliver very fast high current and high voltage pulses straight out of the cavity with out any complicated pulse forming and pulse compression network. Through multistage inductively insulated voltage adders, the output pulse, increased in voltage amplitude, can be applied directly to the load. The load may be a vacuum electron diode, a z-pinch wire array, a gas puff, a liner, an isentropic compression load (ICE) to study material behavior under very high magnetic fields, or a fusion energy (IFE) target. This is because the output pulse rise time and width can be easily tailored to the specific application needs. In this paper we briefly summarize the developmental work done in Sandia and HCEI during the last few years, and describe our new MYKONOS Sandia High Current LTD Laboratory.

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Shaping the output pulse of a linear-transformer-driver module

Proposed for publication in Physical Review Special Topics: Accelerators and Beams.

Stygar, William A.; Stoltzfus, Brian S.; Woodworth, Joseph R.; Fowler, William E.; LeChien, Keith R.; Long, Finis W.; Mazarakis, Michael G.; McKee, George R.; Mckenney, John M.; Savage, Mark E.

We demonstrate that a wide variety of current-pulse shapes can be generated using a linear-transformer-driver (LTD) module that drives an internal water-insulated transmission line. The shapes are produced by varying the timing and initial charge voltage of each of the module's cavities. The LTD-driven accelerator architecture outlined in [Phys. Rev. ST Accel. Beams 10, 030401 (2007)] provides additional pulse-shaping flexibility by allowing the modules that drive the accelerator to be triggered at different times. The module output pulses would be combined and symmetrized by water-insulated radial-transmission-line impedance transformers [Phys. Rev. ST Accel. Beams 11, 030401 (2008)].

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Copy of An overview of pulse compression and power flow in the upgraded Z pulsed power driver

Savage, Mark E.; Maenchen, John E.; McDaniel, Dillon H.; Pasik, Michael F.; Pointon, Timothy D.; Owen, Albert C.; Seidel, David B.; Stoltzfus, Brian S.; Struve, Kenneth W.; Warne, Larry K.; Bennett, Lawrence F.; Woodworth, Joseph R.; Bliss, David E.; Clark, Waylon T.; Coats, Rebecca S.; Elizondo-Decanini, Juan M.; LeChien, Keith R.; Harjes, Henry C.; Lehr, J.M.

Abstract not provided.

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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Viable options for reducing impedance in a 2.5 MV multichanneling, multigap SF6 gas switch

Conference Record of the International Power Modulator Symposium and High Voltage Workshop

LeChien, Keith R.; Gahl, John M.

An investigation was conducted into factors that effect impedance for a 2.5 MV gas switch. The switch studied was Rimfire, the workhorse gas switch topology for many of Sandia's large accelerators. The geometry of the switch investigated consists of multiple self-break gaps in series with a laser triggered main gap. The switch is situated within a coaxial-like ground return structure. In this geometry there are three avenues that are theoretically possible for reducing switch impedance. They are 1) increasing the number of parallel current sharing channels (multichanneling), 2) decreasing the ratio of radii of the outer to inner conductors, and/or 3) decreasing the length. It was experimentally determined what effects the first two factors have on switch impedance and the results are presented in this work. It was discovered that multichanneling and radii ratio have substantially lesser effects on impedance, when compared to the theoretical effects of a reduction in switch length. This leaves reduction in length as the only remaining significant viable option for reduction of impedance in megavolt multigap switches, which has substantial consequences for the future design of multigap switches. ©2006 IEEE.

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26 Results
26 Results