Ohmic-heating-driven electrothermal instability (ETI) as a seed perturbation for standard and helically-oriented magneto-Rayleigh Taylor (MRT) instability on magnetically-driven imploding liners
ORAL · Invited
Abstract
The electrothermal instability (ETI) promotes non-uniform Ohmic heating and expansion about any current-density perturbation in a conductor. This includes the magnetically-driven imploding cylindrical liners (hollow tubes) used in Z Facility experiments, which are driven to 20 MA axial current in 100 ns. As the self-generated magnetic field (Bθ) implodes the liner, azimuthally-correlated magneto-Rayleigh Taylor (MRT) instabilities grow. To achieve thermonuclear neutron production, the Magnetized Liner Inertial Fusion (MagLIF) platform requires the addition of an axial field component (Bz), which results in the development of helically-oriented MRT modes. Ongoing research aims to explain the origins of both azimuthally-correlated and helically-oriented MRT in order to reduce instability growth and improve the performance of various liner platforms.
In this Review, we discuss theory, simulation, and experiment to explore ETI as a seed for both standard and helical MRT. ETI-driven overheating is diagnosed from 1.00-mm-diameter, 10-nm-surface roughness, 99.999%-pure-aluminum rods which are pulsed to 1 MA in 100 ns. Rods include pairs of 10-micron-scale quasi-hemispherical voids or “engineered defects (ED)” which seed ETI, driving local overheating that can be compared with similarly-initiated simulations. Experiments either used a helical return can (HRC) to generate magnetic field at a polarization angle ɸB=arctan(Bz/Bɵ)=15° on the rod’s surface or included no axial field (Bz=ɸB=0). In either case, emissions from individual ED aligned toward ɸB, while emissions from ED within pairs elongated and preferentially merged along ɸB. These data strongly support that for a randomized defect distribution, heating from nearby current-density perturbations will favorably merge about ɸB to generate an extended seed perturbation that aligns toward the surface-field polarization, and this may impact the orientation of subsequent MRT growth on imploding liners.
Sandia National Laboratories is a multimission laboratory managed and operated by NTESS, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE's NNSA under contract DE-NA-0003525.
In this Review, we discuss theory, simulation, and experiment to explore ETI as a seed for both standard and helical MRT. ETI-driven overheating is diagnosed from 1.00-mm-diameter, 10-nm-surface roughness, 99.999%-pure-aluminum rods which are pulsed to 1 MA in 100 ns. Rods include pairs of 10-micron-scale quasi-hemispherical voids or “engineered defects (ED)” which seed ETI, driving local overheating that can be compared with similarly-initiated simulations. Experiments either used a helical return can (HRC) to generate magnetic field at a polarization angle ɸB=arctan(Bz/Bɵ)=15° on the rod’s surface or included no axial field (Bz=ɸB=0). In either case, emissions from individual ED aligned toward ɸB, while emissions from ED within pairs elongated and preferentially merged along ɸB. These data strongly support that for a randomized defect distribution, heating from nearby current-density perturbations will favorably merge about ɸB to generate an extended seed perturbation that aligns toward the surface-field polarization, and this may impact the orientation of subsequent MRT growth on imploding liners.
Sandia National Laboratories is a multimission laboratory managed and operated by NTESS, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE's NNSA under contract DE-NA-0003525.
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Presenters
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Thomas J Awe
Sandia National Laboratories
Authors
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Thomas J Awe
Sandia National Laboratories