The comparison between near-infrared and traditional CO₂ phase contrast imaging on HL-2A tokamak

Highlights: •A near infrared phase contrast imaging on the HL-2A tokamak is designed. •The new diagnostic can measure wavenumber ranging from 2 cm⁻¹ to over 30 cm⁻¹. •NI-PCI has a better response with a size-limited diagnostic window on HL-2A. -- Abstract: The main idea of developing Near Infrared Phase Contrast Imaging (NI-PCI) diagnostic on HL-2A tokamak is presented. Compared to the traditional PCI diagnostic which injects CO₂ laser beam with a wavelength of 10.6 μm into plasma, NI-PCI using 1.55 μm laser has more advantages in measuring plasma density fluctuations due to shorter wavelength. This novel diagnostic is designed to detect plasma density perturbations with a wavenumber ranging from 2 cm⁻¹ to over 30 cm⁻¹ without significant phase scintillation effect. Comparison of diffraction effects between 10.6 μm and 1.55 μm laser beam shows that NI-PCI has a better response than PCI with a size-limited diagnostic window on HL-2A.