Current status and data analysis of BES in EAST

Beam Emission Spectroscopy (BES) diagnostic based on neutral beam injection (NBI) has recently been developed in EAST TOKAMAK. Three cavity interference filter with a center frequency of 659.33 nm and a bandwidth of 1.59 nm is used to eliminate the interference Dα signal and carbon impurities radiation. This BES system diagnoses the plasma density fluctuation with a sample rate of 1 MHz and a spatial resolution of 1-3 cm. It can diagnose a rectangular area in one shot, with a radial length of 20 cm and a vertical length of 10 cm. In the plasma cross section, which is movable from the core plasma to the edge of low field side of EAST by means of changing the angle of the first mirror. Filter test are also presented. Data in the recent experiments of BES show the great change of density fluctuations in the L-H transition. (author)