Development of an upgraded motional Stark effect diagnostic system on EAST tokamak

A new multi-channel motional Stark effect (MSE) diagnostic system has been developed on the upgraded EAST tokamak, which was installed on the port C to observe a tangential neutral beam. A telecentric imaging lens was deployed to ensure uniform illumination from the core to the boundary. A square fiber head which contained 23 fiber bundles was mounted to this imaging lens; each fiber bundle contained 19 fibers and two of them were assigned to CXRS and BES spectrometer, respectively. The angle tuning method was used for matching the Doppler shift of the σ component's wavelength which was caused by the beam voltage. At the present stage, the MSE system only contains ten channels that would be extended to 23 channels in the future, covering a measurement range from R ＝ 1.8 to R ＝ 2.27 m with a temporal resolution of 10 ms and a spatial resolution of 3 cm. The polarization angle-constrained q profiles and current density profiles were reconstructed with EFIT equilibrium reconstructions. In the sawtooth discharges, the q ＝ 1 surface position was validated by the ECE signals, which further verified the rationality of the MSE measurement.