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Traditionally, large-amplitude, fast-rising electrical currents and magnetic fields have been measured with electromagnetic probes such as Rogowski coils or B-dot probes. These measurements can be problematic if made near high voltage electrodes with insufficient probe isolation. An alternative method for measuring electrical current and magnetic fields involves using the Faraday effect on linearly polarized light propagating in single mode fibers.
Faraday effect probes have been used to measure magnetic field strength for many years. In this application, when the fiber probe is subject to a magnetic field, the polarized light will rotate within the fiber. For strong magnetic fields, the rotation angle may exceed many hundreds of degrees with the resultant probe receiver output exhibiting a sinusoidal response. Every signal cycle represents a phase shift equal to 180 degrees (one “fringe shift”), and the magnetic field strength is determined by counting the resultant fringes. Such a probe as this has positive features, including relative immunity to signal cable attenuation, and the fact that optical fiber is a dielectric material which reduces breakdown problems near high voltage electrodes. Furthermore, the response of these probes is based solely on the material properties of the sense fiber, thereby making any calibration, in situ or otherwise, unnecessary. Due to technical advances in the telecommunication industry, a robust compact Faraday effect optical assembly is now available at low cost.
This paper builds on this previous work and summarizes experimental data taken with the Mykonos Linear Transformer Driver (LTD) at Sandia National Laboratories. The Mykonos LTD can output a 1 MA pulse with 60 ns risetime and 160 ns FWHM into a 0.5-Ω matched load. A summary of the results using four Faraday probes, optimized at wavelengths 450 nm, 532 nm, 632 nm and 850 nm is presented.
