Current measurement for four-level magnetically-insulated transmission line

Differential-output current loops (B-dot probes) were designed and calibrated to derive magnetically-insulated transmission line(MITL) current in the PTS facility. Nichrome films were used to shield the loops from sheath electrons. All the B-dots were calibrated insitu. A feeding structure was designed to drive the MITLs from load area. In order to realize uniform current distribution azimuthally, MITL was terminated with short-circuit rods at the end of the corresponding tri-plate water line. Then the B-dots at each level could be calibrated respectively. Frequency response analysis indicates that the using of nichrome film makes the high frequency characteristics worse for B-dots. It shows in experiments that B-dots upper limiting frequency is 50.3 MHz, which is satisfactory for current measurement in our experiments. It also shows that MITL current and load current are self-consistent. Current of each level and combined current of all levels are reasonable according to theoretical predictions.