18–22 Jun 2017
Hilton Brighton Metropole Hotel
Europe/London timezone

HIGH CURRENT SENSING THROUGH FARADAY ROTATION OF POLARIZED LIGHT OF VARYING WAVELENGTHS IN FIBERS

19 Jun 2017, 13:30
1h 30m
Hall 4 / Cambridge (Hilton Brighton Metropole Hotel)

Hall 4 / Cambridge

Hilton Brighton Metropole Hotel

Board: 36
Poster Pulsed Power Physics and Technology, Components and HV Insulation Poster session I - Pulsed Power Physics and Technology, Components and HV Insulation

Speaker

Mr Sean Coffey (SNL)

Description

Traditionally, large-amplitude, fast-rising currents and magnetic fields has been measured with electro-magnetic probes such as Rogowski coils or B-dot probes. Such probes are observed to work satisfactorily for many experimental configurations but the probe to digitizer signal is affected by cabling and cabling elements. Measurements must frequently be made in the presence of significant electromagnetic interference imposing unacceptable levels of noise on the probe signals. Furthermore, probe measurements on high voltage electrodes may be problematic if the probes are not sufficiently isolated. An alternative method for measuring currents and magnetic fields involves using the Faraday effect on linearly polarized light propagating in single mode fibers.
Probes utilizing the Faraday effect have been used for many years. Their operation, whereby the magnetic field strength is proportional to the number of probe output “fringes”, is relatively immune to signal cable attenuation losses. Fibers are dielectrics and their electrical insulation reduces breakdown problems near high voltage electrodes. The probe calibration is a material property so in-situ calibrations are unnecessary. Previously, the Faraday probe setup required an optical engineer to assemble and align the numerous discreet optical elements (i.e. beam expander, splitter, polarizers and focusing optics). This was time consuming work requiring realignment whenever the assembly was moved. Due to tele-communication advancements, a robust compact Faraday effect optical assembly with fixed alignments is now available at low cost.
Also due to these advancements, measurements at many different wavelengths are now possible. Theory predicts the Faraday probe sensitivity is inversely proportional to laser wavelength, thus probes of varying sensitivities can be constructed. This paper details four Faraday probes optimized for wavelengths of 450 nm, 532 nm, 632 nm & 850 nm and includes probe calibration efforts.

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