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Title: Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.

Abstract

Magnetically driven implosions (MDIs) on the Z Facility assemble high-energy-density plasmas for radiation effects and ICF experiments. MDIs are hampered by the Magneto-Rayleigh-Taylor (MRT) instability, which can grow to large amplitude from a small seed perturbation, limiting achievable stagnation pressures and temperatures. The metallic liners used in Magnetized Liner Inertial Fusion (MagLIF) experiments include astonishingly small (-10 nm RMS) initial surface roughness perturbations; nevertheless, unexpectedly large MRT amplitudes are observed in experiments. An electrothermal instability (ETI) may provide a perturbation which exceeds the initial surface roughness. For a condensed metal resistivity increases with temperature. Locations of higher resistivity undergo increased Ohmic heating, resulting in locally higher temperature, and thus still higher resistivity. Such unstable temperature (and pressure) growth produces density perturbations when the locally overheated metal changes phase, providing the seed perturbation for MRT growth. ETI seeding of MRT on thick conductors carrying current in a skin layer has thus far only been inferred by evaluating MRT amplitude late in the experiment. A direct observation of ETI is vital to ensure our simulation tools are accurately representing the seed of the deleterious MRT instability. In this LDRD project, ETI growth was directly observed on the surface of 1.0-mm-diameter solid Almore » rods which were pulsed with 1 MA of current in 100 ns. Fine structures resulting from ETI-driven temperature variations were observed directly through high resolution gated optical imaging. Data from two Aluminum alloys (6061 and 5N) and a variety fabrication techniques (conventional machining, single-point diamond turned, electropolished) enable evaluation of which imperfections provide a seed for ETI growth and subsequent plasma initiation. Data is relevant to the early stages of MagLIF liner implosions, when the ETI seed of MRT may be initiated, and provides a fundamentally new dataset with which to test our state-of-the-art simulation tools.« less

Authors:
; ; ; ; ;  [1];  [1];  [1];  [1];  [2]
  1. UNR
  2. NSTec
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1490531
Report Number(s):
SAND2015-8782
671256
DOE Contract Number:  
AC04-94AL85000
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English

Citation Formats

Awe, Thomas James, Yelton, William G., Yu, Edmund, Rosenthal, Stephen E., McKenzie, Bonnie B., Bauer, Bruno S., Yates, Kevin C., Hutchinson, Trevor M., Fuelling, Stephan, and Lowe, Daniel R. Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.. United States: N. p., 2015. Web. doi:10.2172/1490531.
Awe, Thomas James, Yelton, William G., Yu, Edmund, Rosenthal, Stephen E., McKenzie, Bonnie B., Bauer, Bruno S., Yates, Kevin C., Hutchinson, Trevor M., Fuelling, Stephan, & Lowe, Daniel R. Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.. United States. doi:10.2172/1490531.
Awe, Thomas James, Yelton, William G., Yu, Edmund, Rosenthal, Stephen E., McKenzie, Bonnie B., Bauer, Bruno S., Yates, Kevin C., Hutchinson, Trevor M., Fuelling, Stephan, and Lowe, Daniel R. Thu . "Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.". United States. doi:10.2172/1490531. https://www.osti.gov/servlets/purl/1490531.
@article{osti_1490531,
title = {Direct observation of electrothermal instability structures in the skin layer of an intensely Ohmically heated conductor.},
author = {Awe, Thomas James and Yelton, William G. and Yu, Edmund and Rosenthal, Stephen E. and McKenzie, Bonnie B. and Bauer, Bruno S. and Yates, Kevin C. and Hutchinson, Trevor M. and Fuelling, Stephan and Lowe, Daniel R.},
abstractNote = {Magnetically driven implosions (MDIs) on the Z Facility assemble high-energy-density plasmas for radiation effects and ICF experiments. MDIs are hampered by the Magneto-Rayleigh-Taylor (MRT) instability, which can grow to large amplitude from a small seed perturbation, limiting achievable stagnation pressures and temperatures. The metallic liners used in Magnetized Liner Inertial Fusion (MagLIF) experiments include astonishingly small (-10 nm RMS) initial surface roughness perturbations; nevertheless, unexpectedly large MRT amplitudes are observed in experiments. An electrothermal instability (ETI) may provide a perturbation which exceeds the initial surface roughness. For a condensed metal resistivity increases with temperature. Locations of higher resistivity undergo increased Ohmic heating, resulting in locally higher temperature, and thus still higher resistivity. Such unstable temperature (and pressure) growth produces density perturbations when the locally overheated metal changes phase, providing the seed perturbation for MRT growth. ETI seeding of MRT on thick conductors carrying current in a skin layer has thus far only been inferred by evaluating MRT amplitude late in the experiment. A direct observation of ETI is vital to ensure our simulation tools are accurately representing the seed of the deleterious MRT instability. In this LDRD project, ETI growth was directly observed on the surface of 1.0-mm-diameter solid Al rods which were pulsed with 1 MA of current in 100 ns. Fine structures resulting from ETI-driven temperature variations were observed directly through high resolution gated optical imaging. Data from two Aluminum alloys (6061 and 5N) and a variety fabrication techniques (conventional machining, single-point diamond turned, electropolished) enable evaluation of which imperfections provide a seed for ETI growth and subsequent plasma initiation. Data is relevant to the early stages of MagLIF liner implosions, when the ETI seed of MRT may be initiated, and provides a fundamentally new dataset with which to test our state-of-the-art simulation tools.},
doi = {10.2172/1490531},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2015},
month = {10}
}