Status of edge electron density and temperature measurements with Helium Beam Emission Spectroscopy (He-BES) on EAST

Abstract

Helium Beam Emission Spectroscopy (He-BES) diagnostic has been developed on EAST, which is able to measure the edge electron density and temperature profiles simultaneously using a helium line intensity ratio method. The diagnostic includes the beam injector and the detection system. There are 20 observation channels within an observation range of 80 mm in the detection system at the low filed side, which can cover the whole scrape-off layer (SOL) and part of the pedestal region of EAST. The beam injector system has been upgraded to Supersonic Molecular Beam Injector (SMBI) system to realize deeper helium injection since the 2021 campaign. Four spectral lines at wavelengths of 728.1 nm, 706.5 nm, 667.8 nm and 656.3 nm are detected by the He-BES. The first three spectral lines, including 728.1 nm, 706.5 nm, 667.8 nm, are measured for calculating edge n e and T e profiles based on the collisional-radiative model (CRM) model, and the last spectral line (656.3 nm) is used for the measurement of D α emission. The edge electrostatic fluctuations can be obtained from the power spectrum of D α emission. The electron density and temperature profiles calculated from the 667.8/728.1 and 728.1/706.5 nm line ratios are in good agreement with those from other diagnostics in the edge region of plasma. The self-consistency of He-BES diagnostic is also verified, such as the density pump out caused by LHW and the lower edge temperature caused by the lower heating power.