Phase Contrast Imaging on the HL-2A Tokamak*

In this article we present the design of a phase contrast imaging (PCI) system on the HL-2A tokamak. This diagnostic is developed to infer line integrated plasma density fluctuations by measuring the phase shift of an expanded CO$_{\mathrm{2}}$ laser beam passing through magnetically confined high temperature plasmas. This system is designed to diagnose plasma density fluctuations with the maximum wavenumber of 66 cm$^{\mathrm{-1}}$. The designed wavenumber resolution is 2.09cm$^{\mathrm{-1}}$, and the time resolution is higher than 0.2 $\mu $s. The broad $k\rho_{s} $ ranging from 0.34 to 13.37 makes it suitable for turbulence measurement. An upgraded PCI system is also discussed, which is designed for the HL-2M tokamak.