Towards a 1 MV/1 ns high voltage electro-optic transducer

Many modern pulsed-power techniques, including high current and high energy sources powered by explosive flux compressors, require special instrumentation to measure and record transient voltages that may rise to more than 1 MV in a few nanoseconds. Schemes employing conventional voltage dividers are difficult to use in practice, as problems associated with ground loops and electromagnetic noise are very difficult to overcome. The paper presents a novel design of transducer, which includes both electrical and electro-optic sections. The former is an adjustable fast capacitor voltage-divider, based on a length of 150 kV polyethylene dielectric coaxial cable and with the voltage across the lower section measured with the aid of a Pockels cell. Polarised light from a small HeNe laser is directed at the cell, and the emerging light is received by an electro-optic (EO) converter. When the voltage divider is energised, the change in the light received by the converter is directly dependent on the voltage applied to the capacitor divider. Results are given for a sensor having a rise time of about 2 ns, which has been employed to measure 15 kV pulses. A design for a 1 MV sensor coupled through optical fibres is also presented.