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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. Fri . "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 = {Fri Sep 01 00:00:00 EDT 2017},
month = {Fri Sep 01 00:00:00 EDT 2017}
}

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
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  • As geothermal resources that are more expensive to develop are utilized for power generation, there will be increased incentive to use more efficient power plants. This is expected to be the case with Enhanced Geothermal System (EGS) resources. These resources will likely require wells drilled to depths greater than encountered with hydrothermal resources, and will have the added costs for stimulation to create the subsurface reservoir. It is postulated that plants generating power from these resources will likely utilize the binary cycle technology where heat is rejected sensibly to the ambient. The consumptive use of a portion of the producedmore » geothermal fluid for evaporative heat rejection in the conventional flash-steam conversion cycle is likely to preclude its use with EGS resources. This will be especially true in those areas where there is a high demand for finite supplies of water. Though they have no consumptive use of water, using air-cooling systems for heat rejection has disadvantages. These systems have higher capital costs, reduced power output (heat is rejected at the higher dry-bulb temperature), increased parasitics (fan power), and greater variability in power generation on both a diurnal and annual basis (larger variation in the dry-bulb temperature). This is an interim report for the task ‘Air-Cooled Condensers in Next- Generation Conversion Systems’. The work performed was specifically aimed at a plant that uses commercially available binary cycle technologies with an EGS resource. Concepts were evaluated that have the potential to increase performance, lower cost, or mitigate the adverse effects of off-design operation. The impact on both cost and performance were determined for the concepts considered, and the scenarios identified where a particular concept is best suited. Most, but not all, of the concepts evaluated are associated with the rejection of heat. This report specifically addresses three of the concepts evaluated: the use of recuperation, the use of turbine reheat, and the non-consumptive use of EGS make-up water to supplement heat rejection« 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