A prototype optical voltage sensor for accelerator diagnostic applications

A bulk electro-optic Pockels cell has been designed and tested for noninvasive monitoring of an electron beam or high-voltage conductor. This sensor directly measures the signal of interest rather than the time derivative and is thus attractive for long-pulse applications in the microsecond regime with slow rise times. Additional advantages include a fast response time in the order of 10 ns, low cost and complete galvanic isolation via optical fiber coupling between the sensor and electronics. The Pockels cell modulates the intensity of incident laser light as a function of voltage induced on a discrete electrode which is capacitively coupled to the high-voltage source. Details of the sensor design are presented along with preliminary measurements of a high-current electron beam using a BGO Pockels cell and 850 nm laser diode source.