A Zebra Experiment to Study Plasma Formation by Megagauss Fields

An alternative concept for fusion energy production is magnetized target fusion using metal liners to compress a mixture of magnetic flux and plasma fuel. In liner flux compression experiments, megagauss fields are produced at peak compression that heats the surfaces of aluminum walls of the liner cavity. Some radiation magnetohydrodynamic (MHD) modeling indicates that plasma formation should occur between 3 and 5 MG; however, such modeling depends on assumed material properties, which are a topic of ongoing research. Load hardware and diagnostics have been developed to study metal vapor and plasma formation on aluminum surfaces subjected to pulsed megagauss fields on the University of Nevada Zebra facility. The experiment is designed to study this interesting threshold for plasma formation. A current of 1 MA is pulsed along a stationary central rod to generate magnetic fields of 2-4 MG. The goal is to observe and diagnose the formation of metal vapor and plasma in the vicinity of the rod. The simple geometry enables easy access by diagnostics, which include magnetic sensors, filtered photodiode measurements, optical imaging, and laser schlieren, shadowgraphy, and interferometry. From these measurements, the magnetic field, the temperature of the surface metal plasma, the radiation field, and the growth of instabilities can be inferred. The diagnostics are time resolved to individually examine the distinct phases of heating, surface plasma formation predicted by radiation MHD modeling, and instability.