Simulation of the multi-channel motional Stark effect diagnostic on EAST Tokamak

Abstract

A multi-channel motional Stark effect (MSE) diagnostic is under development for providing accurate information of the internal magnetic field on EAST tokamak. To assist the ongoing design and implementation of the diagnostic, an optimization study is performed using ALCBEAM and NBASS codes. The distribution of the attenuated neutral beam atom density is obtained by ALCBEAM for plasma parameters of Te=2.2keV, neo=1.6×1013cm-3.The MSE spectrum, which is emitted from the beam-plasma interaction and collected by a double-column fiber array with a total number of 19 fibers, is simulated by NBASS on the condition that BT = 2.256 T. The intensity of Dα beam emission for 29 channels is obtained, and the radial spatial resolution ranges from 0.9 cm to 2.3 cm (from edge to core). The influences of the filter’s bandwidth on polarization and transmission are also considered and it is found that 50 % of the polarization and transmission can be achieved when the filter’s bandwidth is around 0.48 nm. For EAST’s MSE system, a 0.48 nm filter is used, which is predicted to have sufficiently high polarization and transmission efficiencies to obtain high-quality MSE signals. When the high voltage of the neutral beam changes, the center wavelength of the spectra shifts. The corresponding central wavelengths for different high voltages of 50 kV, 55 kV and 60 kV are calculated as a function of the major radius. This can serve as a reference for the deployment of the MSE diagnostic.