Regimes of plasma formation and evolution in magnetically insulated transmission lines

Plasma forming from the electrodes of magnetically insulated transmission lines (MITLs) eventually shunts the load, producing MITL closure. An experimental investigation of plasma closure, using coaxial MITLs with anode-cathode gaps 0.5-6.3-mm wide, was performed on a 2-MV, 2-ohm, 100-ns pulse generator (Zebra). When the gap and thus the electric field are gradually changed, the delay between applied voltage and current onset in the MITL gap varies discontinuously, with sudden jumps between distinct MITL operation regimes. For 1.3-2.5-mm gaps the closure begins around the peak current, and the time taken to completely short the gap is within two separate groups. In one case the closure process is fast, occurring within 10-ns, in the other is much slower taking 80-ns. This seems to imply different plasma formation and evolution processes for slightly different conditions. Scenarios of plasma formation and evolution are being modeled with both electromagnetic particle-in-cell and magnetohydrodynamic codes, and are compared with the experimental data.