Fiber-Optic Current Sensor Concept for the T-15MD Tokamak

Abstract

Classic methods for plasma current measurement in tokamaks based on Faraday’s law of induction (Rogowski coil) or the Hall effect (Hall sensor) have a number of disadvantages that can be most acute in fusion reactor steady-state operating regimes (strong stray fields, operation in a long pulse with a constant plasma current). To ensure reliability of the measurements, the use of current sensors based on other physical principles may be required. Such a sensor is a fiber-optic current sensor (FOCS) based on the magneto-optic effect (Faraday effect). An analysis of international experience in FOCS application for plasma current measurements (JET, EAST, Tore-Supra tokamaks, etc.) was carried out in this work. Based on analysis, the concept of an improved FOCS measurement scheme for the T-15MD tokamak was proposed. The proposed FOCS reflective (double-pass) circuit, operating on the interferometer principle with probing at an intermediate frequency, will make it possible to carry out measurements over the entire designed range of plasma currents (up to 2 MA) with an error of 0.5 kA and a time resolution of 100 μs.