Development And Application Of Fiber Optic Current Sensor On EAST Tokamak

Measuring the plasma current and the poloidal field(PF)current with a high ac-curacy is a basic requirement for the operation of a tokamak.Fiber optic current sen-sors(FOCS),based on the Faraday Effect,are one of the best choices to measure the plasma current and the PF current in a steady-state discharge.A fiber optic current measurement system consists of 2 fiber optic current sensors for the plasma current measurement and 12 FOCS for the PF current measurement was installed on the Exper-imental Advanced Superconducting Tokamak(EAST).To meet the PF busbars current measurement accuracy requirement(0.2%),the FOCS sensor heads were calibrated for a temperature range between-5℃ and 55℃.Allan Variance has been used on FOCS noise analysis,the FOCS noise has been reduced based on the analysis result.To reduce the sensor head magnetic crosstalk,a model has been developed and validated for FOCS sensor heads.When used to sense the EAST PF busbars current during experiments,the FOCS showed excellent performance.To the FOCS for the plasma current measurement,the sensing optical fiber is in-stalled inside the EAST vacuum vessel(VV)while the signal processing system is kept outside the vacuum vessel,close to the EAST.For EAST,the VV would bake at high temperature before every campaign.When the EAST is operating,the variations in the magnetic field will trigger vibrations and even shocks;nuclear reactions will produce a lot of radiation and there are strong electromagnetic waves around the EAST.We have tested the influence of high temperature,vibrations and shocks,nuclear radiation and electromagnetic interference on FOCS.We have developed and assembled a polariza-tion maintaining optical fiber bulkhead connector to guide the optical fiber out of EAST vacuum vessel.These two FOCS have been carefully calibrated and compensated for its scale coefficient nonlinearity.In EAST experiment,the FOCS has achieved the plasma current measurement up to 800KA.Furthermore,the FOCS has responded to the rapid change in current during the plasma disruption.From the results in a different range of the plasma current shots,these FOCS performed very well to sense the plasma current of the EAST.