Development and preliminary results of phase contrast imaging diagnostic on HL-2A

Phase Contrast Imaging (PCI) diagnostic has been developed on HL-2 A tokamak. The chord integral density fluctuations of plasma can be obtained by measuring the phase shift of CO2 laser which has a wavelength of 10.6 mu m after passing through plasma. The 32-channel detector array enables PCI to diagnose density fluctuations with wavenumbers ranging from 2 cm(-1) to 15 cm(-1). The temporal resolution of PCI is better than 2 mu s which makes it suitable for broadband turbulence research. Calibration by the sound source confirms that PCI is able to discriminate a wide range of wavenumbers. The plasma density fluctuations measured by PCI on HL-2 A is presented for the first time. Comparison of MHD instability investigations with magnetic probe data shows the reliability of this PCI diagnostic.