Demonstration of Megagauss-level Premagnetization and Cylindrical Implosion Symmetry in Auto-magnetizing Liner Experiments for Magnetized Liner Inertial Fusion (MagLIF)

Gabriel Shipley, University of New Mexico

Photo of Gabriel Shipley

Auto-magnetizing liners (AutoMag) are designed to generate strong axial magnetic fields inside of the fusion fuel column in magnetized liner inertial fusion (MagLIF) without the need for external field coils. AutoMag liners are cylindrical tubes made of metallic helical conductors separated by electrically insulating material. In the first stage of AutoMag, helical current flows in the liner and produces a strong internal axial field (20 to 100 T) during an about 5 kA/ns current prepulse that lasts about 200 ns. In the second stage, the rapidly rising main current pulse (200 kA/ns) induces a strong electric field in the liner that causes the insulating material to undergo dielectric breakdown. Liner current then reorients from helical to predominantly axial, ceasing the AutoMag Bz production mechanism and the z-pinch liner implodes as the current rises to 20 MA in 100 ns. Proof-of-concept experiments on the Mykonos linear transformer driver (about 500 kA in 125 ns) evaluated the efficacy of the AutoMag premagnetization concept. Conservatively wound liners maintained helical current flow through peak current, reliably generating Bz from 20 T to 40 T in agreement with prediction. More aggressively wound liners demonstrated Bz up to 90 T despite some helical shorting during the current rise. Recent AutoMag experiments on the Z Facility demonstrated production of Bz greater than 100 T during a 2 MA prepulse and used radiography to determine the liner's implosion integrity. Despite AutoMag's initially 3-D density and conductivity topology, radiography data shows that AutoMag liners on Z implode with a high level of cylindrical symmetry. The AutoMag experiments on Z, the first of their kind, support an advance in magneto-inertial fusion that will enable the design of MagLIF targets capable of reaching higher current delivered to the liner (better fuel compression) and stronger magnetization inside of the fusion fuel (better thermal insulation).

Abstract Author(s): G.A. Shipley, T.J. Awe, B.T. Hutsel, S.A. Slutz, J.B. Greenly, C.A. Jennings, D.C. Lamppa, T.M. Hutchinson