Development of a passive visible spectroscopic diagnostic on HL-2A

A passive visible spectroscopic diagnostic which may measure the profiles of line emission and continuum radiation simultaneously is first installed on HL-2A tokamak. The line-integrated brightness profiles covering the whole plasma cross section are measured with the spatial resolution of 2.7 cm and temporal resolution of 10 ms. Graphite plates to face the objective are installed on the inner vessel wall, which reduces the influence of wall reflection on the optical measurements. A local relatively-low temperature region, located at the plasma edge above the mid-plane and caused by plasma-baffle interaction, is confirmed by this diagnostic. The obvious increase of the line-averaged Z_eff during auxiliary heating discharge is mainly due to the inward impurity diffusion. Assumed Z_eff with flat profiles in Ohmic and NBI discharges, the line-integrated electron density profiles measured by the visible bremsstrahlung are in good agreement with the ones measured by the FIR interferometer.