Tomography of emissivity for Doppler coherence imaging spectroscopy diagnostic in HL-2A

A newly developed Doppler coherence imaging spectroscopy (CIS) technique has been implemented in the HL-2A tokamak for carbon impurity emissivity and flow measurement. In CIS diagnostics, the emissivity and flow profiles inside the plasma are measured by a camera from the line-integrated emissivity and line-averaged flow, respectively. A standard inference method, called tomographic inversion, is necessary. Such an inversion is relatively challenging due to the ill-conditioned nature. In this article, we report the recent application and comparison of two different tomography algorithms, Gaussian process tomography and Tikhonov tomography, on light intensity measured by CIS, including feasibility and benchmark studies. Finally, the tomographic results for real measurement data in HL-2A are presented.