Simultaneous measurements of the poloidal magnetic field distribution in JET by means of the Faraday and motional Stark effects are reported. The experiments were designed to minimize the errors resulting from a noncircular flux surface geometry and from a limited spatial resolution. Both techniques show that full reconnection of the flux inside the q=1 surface does not occur during a sawtooth collapse
A fast, magnetics-free flux surface estimation and q-profile reconstruction algorithm for feedback control of plasma profiles