Progress of plasma density fluctuation measurements with phase contrast imaging on HL-2A tokamak

A CO2 laser-based phase contrast imaging (PCI) diagnostic has been developed on HL-2A tokamak. It can detect line integrated plasma density fluctuations by measuring the phase shift of laser beam after being scattered by the bulk plasma. The diagnosed radial region ranges from rho r/a = 0.625 to 0.7. 32-channel HgCdTe detectors with alternative-current biased amplifiers are arranged in line at the imaging plane of the optical path. This PCI is able to diagnose density fluctuations with wavenumbers ranging from 2 to 15 cm(-1) and the time resolution is better than 2 mu s. The first experimental data were achieved in 2018 spring campaign of HL-2A tokamak. High performance is confirmed in different discharging configurations and makes it a keen tool in broadband turbulence investigations.