The motional Stark effect polarimeter in the HL-2A tokamak

Abstract

A 7-channel motional Stark effect polarimeter based on four polarizers and a spectrometer has been developed in the HL-2A tokamak, which is the first time successful utilizing this kind of polarimeter on a tokamak. The accuracy of the angle can reach ±0.25° in the calibration experiments. Pilot experiments of measuring the magnetic pitch angle have been successfully carried out in the weak motional Stark effect plasma discharge with toroidal magnetic field of ~1.3 T and beam energy of ~25 keV/amu. The pitch angles of magnetic field are obtained for 7 spatial points covering 24 cm along major radius with time resolution of 40 ms; the profiles of safety factor are obtained by combining with the Equilibrium and Reconstruction Fitting Code. The core value of safety factor (q) is less than 1 during the sawtooth oscillation and the position of q = 1 surface is well consistent with the results measured by soft X-ray array.

Ion internal transport barrier in neutral beam heated plasmas on HL-2A

“…The movement of the q = 1 surface can be verified by the equilibrium and reconstruction fitting code (EFIT). At HL-2A, a motional Stark effect polarimeter (MSE) is available for some shots [16], and EFIT can be validated by MSE measurements in other shot. iITBs are more frequently observed at the beginning of the NBI heating phases accompanied by LLM.…”

Bayesian soft x-ray tomography and MHD mode analysis on HL-2A

“…A good understanding of MHD activities is important to improve the tokamak operations. Future work will aim to combine more MHD relevant diagnostics that already exist or are under development on HL-2A [30][31][32], eventually achieving a comprehensive analysis of the MHD instabilities. The diag nostics to be combined include ECE which can detect the perturbation of the electron temperature at the plasma edge, as well as the MSE diagnostics which can provide an accurate prediction of safety factor particularly at the plasma center.…”