Beam Emission Spectroscopy Measurements on KSTAR

Beam emission spectroscopy measures electron density from the Doppler-shifted light emission of a heating beam excited by beam-plasma particle collisions [1]. From the measured light intensity one can calculate the electron density after proper calibration. If sufficient light is available, this technique enables us the study of electron density fluctuations and their spatial distribution via two-dimensional detectors. Before the system design, detailed modelling was performed in order to calculate the expected photon flux at the BES port, which resulted at 1× 1010− 5× 1010 photons s . According to modelling results for the calculated photon flux and 1MHz bandwidth, the optimal detector type was the avalanche photo diode (APD). A trial BES measurement system was designed and built for validating the modelling and to prove the feasibility of the BES technique on KSTAR. The trial KSTAR BES system measured the light emission from the 80-90keV heating deuterium neutral beam. The diagnostic was placed inside a port already foreseen for this purpose in the machine design, 45 degrees away from the NBI port (see Fig. 1).