Public Abstract

DE-SC0012328: Mitigation of Magneto Rayleigh Taylor Instability

Award Status: Inactive

Institution: Regents of the University of Michigan, Ann Arbor, MI
UEI: GNJ7BBP73WE9
DUNS: 073133571

Most Recent Award Date: 04/14/2017
Number of Support Periods: 3
PM: Akli, Kramer

Current Budget Period: 08/15/2016 - 02/14/2018
Current Project Period: 08/15/2014 - 02/14/2018
PI: Lau, Yue-Ying

Supplement Budget Period: N/A

Public Abstract

This proposal investigates the mitigation of the magneto-Rayleigh-Taylor instability (MRT). MRT is important to magnetized target fusion, wire-array z-pinches, and equation-of-state studies using flyer plates or isentropic compression. It is also important to the study of the crab nebula. In the contemporary concept of magnetized target fusion (MagLIF) pioneered at the Sandia National Laboratories, MRT on the surfaces of the cylindrical liner is a major concern. This proposal explores novel methods on MRT mitigation, using magnetic shear and pulse shaping. The theory developed will be tested in experiments, using the mega-ampere linear transformer driver (LTD) that was constructed at the Investigators’ laboratory at the University of Michigan. This is the first mega-amp class LTD in the USA. In the MagLIF concept, during the risetime of the axial current, the azimuthal magnetic field may diffuse into the liner, possibly creating a strong radial dependence of the azimuthal magnetic field and therefore a strong magnetic shear within the liner, offering the interesting possibility of shear stabilization of MRT. Effects of magnetic shear on MRT will be studied. A stellerator-like, coiled return current post will be tested on a metal foil plasma driven by the 1-MA LTD. The Investigators have constructed a versatile, easy-to-apply, analytic solution for MRT on a finite plasma slab that is accelerated by an arbitrary combination of magnetic pressure and fluid pressure. The magnetic field in different regions may assume arbitrary magnitude and direction tangential to the interfaces. The temporal evolution of initial surface ripples was obtained. From the closed form solution, a variational technique will be applied to determine the optimal current pulse shape that minimizes the MRT growth. Experimentally, the optimal pulse shape may be synthesized by the 40 switches of the LTD which can be triggered independently. Other topics of substantial interest to high energy density plasmas will also be studied: (a) evolution of surface ripples from implosion through stagnation on cylindrical liners, (b) effects of shocks on feedthrough, (c) seeding of MRT by multi-wavelengths, and (d) unique cylindrical effects such as the inevitable coupling between MRT, kink, and sausage modes. The intellectual merit includes: (A) an innovative study of the effects of magnetic shear on MRT, (B) an optimal design of the current pulse shape that minimizes MRT growth, (C) a novel analytic formulation of surface ripples from implosion to stagnation, including the effect of shocks on feedthrough, that is bench marked against the advanced simulation code, HYDRA, which was developed at the Lawrence Livermore National Laboratory, and (D) a penetrating study of cylindrical effects such as the coupling of MRT-kink-sausage modes and the Bell-Plesett effects. The broader impacts include MRT mitigation, the most serious concern to magnetized target fusion, which is a hybrid between magnetic and inertial confinement that could significantly reduce the cost and complexity of achieving fusion gain. The most general MRT solution to date with arbitrary magnetic field (including magnetic shear) and arbitrary kinetic pressure, is widely applicable to laboratory and astrophysical plasmas, and bench-marked with HYDRA. One of the most significant impacts of this research will be continued training of graduate and undergraduate students in high energy density plasma physics as well as optical and laser diagnostics. They will also be trained in the latest LTD technology. They are educated in an environment where theory, simulation, and experiments are fully integrated, including internship in DoE and DoD laboratories and in industry. Over 50 PhDs have been trained and graduated by the University of Michigan Co-Principal Investigators over the past three decades in their Plasma, Pulsed Power and Microwave Laboratory. Quite a few of them have become the leaders in the field, including Fellows in professional societies.

This proposal investigates the mitigation of the magneto-Rayleigh-Taylor instability (MRT). MRT is important to magnetized target fusion, wire-array z-pinches, and equation-of-state studies using flyer plates or isentropic compression. It is also important to the study of the crab nebula. In the contemporary concept of magnetized target fusion (MagLIF) pioneered at the Sandia National Laboratories, MRT on the surfaces of the cylindrical liner is a major concern. This proposal explores novel methods on MRT mitigation, using magnetic shear and pulse shaping. The theory developed will be tested in experiments, using the mega-ampere linear transformer driver (LTD) that was constructed at the Investigators’ laboratory at the University of Michigan. This is the first mega-amp class LTD in the USA.

In the MagLIF concept, during the risetime of the axial current, the azimuthal magnetic field may diffuse into the liner, possibly creating a strong radial dependence of the azimuthal magnetic field and therefore a strong magnetic shear within the liner, offering the interesting possibility of shear stabilization of MRT. Effects of magnetic shear on MRT will be studied. A stellerator-like, coiled return current post will be tested on a metal foil plasma driven by the 1-MA LTD.

The Investigators have constructed a versatile, easy-to-apply, analytic solution for MRT on a finite plasma slab that is accelerated by an arbitrary combination of magnetic pressure and fluid pressure. The magnetic field in different regions may assume arbitrary magnitude and direction tangential to the interfaces. The temporal evolution of initial surface ripples was obtained. From the closed form solution, a variational technique will be applied to determine the optimal current pulse shape that minimizes the MRT growth. Experimentally, the optimal pulse shape may be synthesized by the 40 switches of the LTD which can be triggered independently.

Other topics of substantial interest to high energy density plasmas will also be studied: (a) evolution of surface ripples from implosion through stagnation on cylindrical liners, (b) effects of shocks on feedthrough, (c) seeding of MRT by multi-wavelengths, and (d) unique cylindrical effects such as the inevitable coupling between MRT, kink, and sausage modes.

The intellectual merit includes: (A) an innovative study of the effects of magnetic shear on MRT, (B) an optimal design of the current pulse shape that minimizes MRT growth, (C) a novel analytic formulation of surface ripples from implosion to stagnation, including the effect of shocks on feedthrough, that is bench marked against the advanced simulation code, HYDRA, which was developed at the Lawrence Livermore National Laboratory, and (D) a penetrating study of cylindrical effects such as the coupling of MRT-kink-sausage modes and the Bell-Plesett effects.

The broader impacts include MRT mitigation, the most serious concern to magnetized target fusion, which is a hybrid between magnetic and inertial confinement that could significantly reduce the cost and complexity of achieving fusion gain. The most general MRT solution to date with arbitrary magnetic field (including magnetic shear) and arbitrary kinetic pressure, is widely applicable to laboratory and astrophysical plasmas, and bench-marked with HYDRA.

One of the most significant impacts of this research will be continued training of graduate and undergraduate students in high energy density plasma physics as well as optical and laser diagnostics. They will also be trained in the latest LTD technology. They are educated in an environment where theory, simulation, and experiments are fully integrated, including internship in DoE and DoD laboratories and in industry. Over 50 PhDs have been trained and graduated by the University of Michigan Co-Principal Investigators over the past three decades in their Plasma, Pulsed Power and Microwave Laboratory. Quite a few of them have become the leaders in the field, including Fellows in professional societies.