The effect of surface roughness and structure on subsequent magneto-Rayleigh-Taylor instability growth in beryllium liner implosions on Z

Summary form only given. Sandia is investigating a new magnetized liner inertial fusion (MagLIF) concept that uses cylindrical Be or Al liners to compress magnetized and preheated fusion fuel. As part of this work, we have been studying the growth of instabilities in initially solid liners driven with 20-24 MA, 100-ns current pulses on the Z pulsed power facility. The magneto-Rayleigh-Taylor instability in particular can disrupt the plasma liner during its implosion. A remarkable degree of azimuthal symmetry is observed near stagnation in beryllium liner implosions. This symmetry is captured in 3D calculations only when some azimuthally correlated perturbations are seeded initially. One possibility is that the MRT instability is directly seeded by azimuthally correlated, fine-scale structures on the surface that result from diamond turning the liner on a lathe. A second possibility is that the electro-thermal instability is seeding the MRT instability. Simulations suggest that the level of instability growth seeded by the ET instability is not strongly dependent on the surface roughness. Understanding the surface finish requirements for liner implosions is an important practical question. We will discuss the results of experiments in which the surface of Be liners was altered by polishing the liners along the axial direction after machining. This removes the azimuthally correlated structure, leaving only axially correlated grooves. The latter should noticeably affect the growth of MRT if the surface structure is directly seeding the instability, but may not have any impact if the ET instability is the dominant seed.