Fiber-optic current sensor for plasma current on experimental advanced superconducting tokamak

Abstract

The plasma current is an essential parameter for tokamak operation. Fiber optic current sensors, based on the Faraday Effect, are one of the best choices to measure the plasma current in a steady-state discharge. Such an fiber-optic current sensor (FOCS) was successfully installed on the Experimental Advanced Superconducting Tokamak (EAST). The FOCS is a closed-loop FOCS, based on a polarization-rotated reflection interferometer. The sensing optical fiber is installed inside the EAST vacuum vessel while the signal processing system is kept outside the vacuum vessel. In order to guide the optical fiber out of EAST vacuum vessel, we have developed and assembled a polarization maintaining optical fiber bulkhead connector. When the tokamak device is operating, the variations in the magnetic field will give rise to vibrations and even shocks. We have tested the influence of vibrations and shocks on fiber-optic current sensor. In EAST experiment, the FOCS has achieved the plasma current measurement up to 800 kA. Furthermore, the FOCS has responds to the rapid change in current during the plasma disruption. From the results from a different range of plasma current shots, the fiber-optic current sensor performed very well to sense the plasma current of the EAST.