Stabilizing Liner Implosions with a Dynamic Screw Pinch

Pulsed power driven liner implosions are susceptible to instabilities like the magneto Rayleigh-Taylor (MRT) instability. One proposed method for mitigating MRT uses the rotating magnetic field of a dynamic screw pinch, which can be generated using a twisted return current structure. This method has been examined in computer simulations and now in experiments as well. Using the COBRA pulsed power driver, both straight and twisted return current paths were tested on imploding thin-foil liners, made from 650 nm thick aluminum foil. Each implosion was driven by a current pulse that rose from 0 to 1 MA in 100 ns. Three different twisted return current structures were tested with peak axial magnetic fields ranging from 2 T to 20 T. These experiments revealed remarkable differences in the instability structures between the cases. Helical modes were observed for the twisted return can cases and were absent from the normal z-pinch case. The amplitudes of the MRT spikes were also reduced, by up to a factor of two, at the time of liner stagnation on a central support rod, at a convergence ratio of about two.

Work supported by NSF Grant PHY-1705418. COBRA support provided by the NNSA SSAP under DOE Cooperative Agreement DE-NA-0003764.