Feedthrough of the Magneto-Rayleigh-Taylor instability in the presence of a shock

M R Weis,R M Gilgenbach,M Hess,K J Peterson,Y Y Lau

doi:10.1109/plasma.2014.7012641

M R Weis, R M Gilgenbach + Show 3 more

https://doi.org/10.1109/plasma.2014.7012641

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The success of the Magnetized Liner Inertial Fusion (MagLIF) campaign requires successful mitigation of the Magneto-Rayleigh-Taylor instability (MRT). Initially, the exterior of the liner is MRT unstable; as the accelerated liner compresses a fill gas, it is eventually decelerated by the back pressure of the fill gas causing the inner surface to become MRT unstable. It is thought that feedthrough of MRT from the outer to inner surface can provide a seed for disruptive growth in the deceleration phase. A common method of studying MRT is by machining sinusoidal ripples on the exterior of metal targets (Al, Be in particular). This seeding provides a known wavelength for MRT whose growth can then be compared with linear theory. For the exterior of Al liners, linear MRT theory works quite well [1] and thus, feedthrough theory should apply equally well to the inner surface for an unshocked seeded liner. However, in most shots on the Z-machine a shock is driven through the liner. 2D HYDRA simulations show the shock is rippled with the seeded wavelength and imprints this ripple on the inner surface as it breaks-out. The amplitude of this ripple could be much larger than what would be expected from the feedthrough of MRT theory [2]. Thus, to study feedthrough directly either isentropic compression is required, or we must include the effect of the shock on feedthrough. We propose a simple model to determine the imprinted ripple amplitude from a shock and then calculate the evolution of the inner surface ripple using traditional MRT [2] and Richtmyer-Meshkov theory and then compare to 2D HYDRA results. This model allows for simultaneous study of outer/inner surface growth from an exterior seeded perturbation and includes the effect of feedthrough. We also examine the impact of axial magnetic fields and fill gases (cool and pre-heated) on feedthrough and shock imprinting by applying our model and compare with 2D simulations.

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