Optically isolated E-field detector

The Atlas Marx design will require a total of 192 spark-gaps of the DNA/Maxwell ´Rail-Gap´ type. This Rail-Gap configuration was selected for its inherent low inductance when used in the folded, axial-capacitor scheme used in the Atlas Marx design. The current fed toward the center of the machine must arrive (from 24 radial, bank sources) within a certain restrictive time frame such that the target is fed by an azimuthally-pure current sheet. Timing 192 spark type switches within a 10-20 ns time frame might be compared with the difficulties of herding cats. Knowing when each of the Rail-Gaps has collapsed into a low resistive state would aid certainly in initial machine setup but also should be historic information recorded for each experiment so that target perturbations might be explained. There are many other reasons for having the ability to observe the switch actions such as trigger system diagnostics, switch aging and pre-trigger management, etc. The authors have developed a simple and effective fiber-optically isolated detector that can be mounted on the face of each of the Rail-Gaps. These ´bat-wing´ or ´bow-tie´ detectors, as they have become known, produce a bright signal in the fiber driven by the collapsing E-field both in the full charged mode but also when only the trigger is fired (no charge on the bank capacitors).