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Title: Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators

Abstract

We have developed two advanced designs of a field-distortion air-insulated spark-gap switch that reduce the size of a linear-transformer-driver (LTD) brick. Both designs operate at 200 kV and a peak current of ~50 kA. At these parameters, both achieve a jitter of less than 2 ns and a prefire rate of ~0.1% over 5000 shots. We have reduced the number of switch parts and assembly steps, which has resulted in a more uniform, design-driven assembly process. We will characterize the performance of tungsten-copper and graphite electrodes, and two different electrode geometries. The new switch designs will substantially improve the electrical and operational performance of next-generation pulsed-power accelerators.

Authors:
 [1];  [1];  [1];  [1];  [2];  [1];  [1];  [1];  [1];  [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. Kinetech LLC, Cedar Crest, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1395749
Report Number(s):
SAND-2017-10300
657236
DOE Contract Number:
AC04-94AL85000; NA0003525
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 36 MATERIALS SCIENCE

Citation Formats

Wisher, Matthew Louis, Johns, Owen M., Breden, Eric Wayne, Calhoun, Jacob Daniel, Gruner, Frederick Rusticus, Hohlfelder, Robert James, Mulville, Thomas D., Muron, David J., Stoltzfus, Brian S., and Stygar, William A. Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators. United States: N. p., 2017. Web. doi:10.2172/1395749.
Wisher, Matthew Louis, Johns, Owen M., Breden, Eric Wayne, Calhoun, Jacob Daniel, Gruner, Frederick Rusticus, Hohlfelder, Robert James, Mulville, Thomas D., Muron, David J., Stoltzfus, Brian S., & Stygar, William A. Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators. United States. doi:10.2172/1395749.
Wisher, Matthew Louis, Johns, Owen M., Breden, Eric Wayne, Calhoun, Jacob Daniel, Gruner, Frederick Rusticus, Hohlfelder, Robert James, Mulville, Thomas D., Muron, David J., Stoltzfus, Brian S., and Stygar, William A. 2017. "Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators". United States. doi:10.2172/1395749. https://www.osti.gov/servlets/purl/1395749.
@article{osti_1395749,
title = {Field-Distortion Air-Insulated Switches for Next-Generation Pulsed-Power Accelerators},
author = {Wisher, Matthew Louis and Johns, Owen M. and Breden, Eric Wayne and Calhoun, Jacob Daniel and Gruner, Frederick Rusticus and Hohlfelder, Robert James and Mulville, Thomas D. and Muron, David J. and Stoltzfus, Brian S. and Stygar, William A.},
abstractNote = {We have developed two advanced designs of a field-distortion air-insulated spark-gap switch that reduce the size of a linear-transformer-driver (LTD) brick. Both designs operate at 200 kV and a peak current of ~50 kA. At these parameters, both achieve a jitter of less than 2 ns and a prefire rate of ~0.1% over 5000 shots. We have reduced the number of switch parts and assembly steps, which has resulted in a more uniform, design-driven assembly process. We will characterize the performance of tungsten-copper and graphite electrodes, and two different electrode geometries. The new switch designs will substantially improve the electrical and operational performance of next-generation pulsed-power accelerators.},
doi = {10.2172/1395749},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 9
}

Technical Report:

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  • Future pulsed power systems may rely on linear transformer driver (LTD) technology. The LTD's will be the building blocks for a driver that can deliver higher current than the Z-Machine. The LTD's would require tens of thousands of low inductance ( %3C 85nH), high voltage (200 kV DC) switches with high reliability and long lifetime ( 10 4 shots). Sandia's Z-Machine employs 36 megavolt class switches that are laser triggered by a single channel discharge. This is feasible for tens of switches but the high inductance and short switch life- time associated with the single channel discharge are undesirable formore » future machines. Thus the fundamental problem is how to lower inductance and losses while increasing switch life- time and reliability. These goals can be achieved by increasing the number of current-carrying channels. The rail gap switch is ideal for this purpose. Although those switches have been extensively studied during the past decades, each effort has only characterized a particular switch. There is no comprehensive understanding of the underlying physics that would allow predictive capability for arbitrary switch geometry. We have studied rail gap switches via an extensive suite of advanced diagnostics in synergy with theoretical physics and advanced modeling capability. Design and topology of multichannel switches as they relate to discharge dynamics are investigated. This involves electrically and optically triggered rail gaps, as well as discrete multi-site switch concepts.« less
  • This LDRD project was developed around the ambitious goal of applying PDE-constrained opti- mization approaches to design Z-machine components whose performance is governed by elec- tromagnetic and plasma models. This report documents the results of this LDRD project. Our differentiating approach was to use topology optimization methods developed for structural design and extend them for application to electromagnetic systems pertinent to the Z-machine. To achieve this objective a suite of optimization algorithms were implemented in the ROL library part of the Trilinos framework. These methods were applied to standalone demonstration problems and the Drekar multi-physics research application. Out of thismore » exploration a new augmented Lagrangian approach to structural design problems was developed. We demonstrate that this approach has favorable mesh-independent performance. Both the final design and the algorithmic performance were independent of the size of the mesh. In addition, topology optimization formulations for the design of conducting networks were developed and demonstrated. Of note, this formulation was used to develop a design for the inner magnetically insulated transmission line on the Z-machine. The resulting electromagnetic device is compared with theoretically postulated designs.« less
  • Focused Beams from high-power lasers have been used to command trigger gas switches in pulse power accelerators for more than two decades. This Laboratory-Directed Research and Development project was aimed at determining whether high power lasers could also command trigger water switches on high-power accelerators. In initial work, we determined that focused light from three harmonics of a small pulsed Nd:YAG laser at 1064 nm, 532 nm, and 355 nm could be used to form breakdown arcs in water, with the lowest breakdown thresholds of 110 J/cm{sup 2} or 14 GW/cm{sup 2} at 532 nm in the green. In laboratory-scalemore » laser triggering experiments with a 170-kV pulse-charged water switch with a 3-mm anode-cathode gap, we demonstrated that {approx}90 mJ of green laser energy could trigger the gap with a 1-{sigma} jitter of less than 2ns, a factor of 10 improvement over the jitter of the switch in its self breaking mode. In the laboratory-scale experiments we developed optical techniques utilizing polarization rotation of a probe laser beam to measure current in switch channels and electric field enhancements near streamer heads. In the final year of the project, we constructed a pulse-power facility to allow us to test laser triggering of water switches from 0.6- MV to 2.0 MV. Triggering experiments on this facility using an axicon lens for focusing the laser and a switch with a 740 kV self-break voltage produced consistent laser triggering with a {+-} 16-ns 1-{sigma} jitter, a significant improvement over the {+-} 24-ns jitter in the self-breaking mode.« less
  • Abstract not provided.