Measurement of 2-5 MV pulsed-voltages in electron beam diodes from Compton generated electrons

Summary form only given, as follows. Measuring multi-megavolt voltages across pulsed electron-beam diodes is very difficult. A capacitive probe can measure the voltage in the water or oil transmission line feeding power to the diode. However, this is usually far electrically from the diode and an inductive correction is usually applied to obtain the diode voltage. The two main problems with the inductive correction technique are: a) the inductance must be known, usually requiring additional short-circuit shots and b) derivatives of the current and transmission line effects introduce large errors in the measurement. Because of these difficulties researchers have devised several alternative methods for measuring the diode voltage. One method is based on analyzing the bremsstrahlung radiation produced in the diode through depth-dose stacks. Depth-dose stacks work well for voltages below 2 MV but fail at higher voltages because the mass attenuation coefficient becomes insensitive to voltage. Other alternatives based on known nuclear reactions have also been used but are also difficult at high voltages and provide no time behavior. Another alternative is to analyze the electrons generated by the bremsstrahlung spectrum through Compton collisions. In this method, photons generated in the diode are collimated onto an aluminum target. The Compton-generated electrons that escape the target are bent by a strong magnetic field and detected in a plane perpendicular to the Compton target. Electron/photon transport calculations from previous work showed that the ratio of the Compton electron dose to the photon dose is sensitive to the diode voltage in the 1-2 MV range. Proof-of-principle experiments using CaF/sub 2/ dosimeters for both the electrons and photons were also performed on a DC van de Graaff generator and results were in good agreement with the calculations. In this work we will use the ITS/Accept Monte-Carlo electron/photon transport code to extend the voltage range - p to 5 MV and use active detectors to obtain a time-dependent voltage measurement. Time-dependent data from this voltage monitor from various pulsed-power machines will be presented and compared with the Accept calculations.