Origin of the B-dot Jump Observed in Precision Liner Experiments

In the liner-ejecta experiments carried out at the Los Alamos pulsed power facility Pegasus II, a solid liner was magnetically imploded to impact on a target cylinder to produce the shockinduced ejecta. As a result of improved time resolution for the B-dot (dB/dt) probes fielded last fall, we began to notice a sharp jump in the B-dot curve occurring at a time very close to the expected liner-target collision time. This jump was also found in the time derivative of the calculated current ( di/ dt) obtained from code simulation. We have shown that the jump is indeed caused by the collision as a sudden change of the liner velocity would induce a sudden jump in the time derivative of the inductance. We have derived a general formula for calculating the jump in di/dt and verified that the result computed from it is in good agreement with the code simulation. Useful diagnostic applications of the B-dot jump are discussed.