Finite system response shape due distortions of the temperature and density profiles in fusion plasmas recovered using Thomson scattering lidar

摘要

The performed analysis reveals interesting and useful features of the distortions of the measured Thomson scattering lidar profile, and the corresponding recovered temperature and density profiles, due to convolution of the lidar response function with the maximum-resolved lidar profile obtainable at a delta-like system response. It is shown that in the case of a symmetric pulse response, far from the pedestal area at the plasma edge, the convolution does not distort the information about the smooth-enough line-of-sight distribution of the electron temperature and density. In the pedestal area such distortions exist. They concern mainly the steep density profiles and depend on the temperature profile steepness. In practice, the temperature profiles are slanting-enough around the pedestal. Then the center-of-mass wavelength and the fitting approaches provide the undistorted temperature profile, and the latter approach provides the density profile convolved with the response function. In the case of an asymmetric system response, distortions of the information about the density distribution exist along the whole line of sight within the plasma torus. They depend on the variability of the electron temperature and density profiles and could be minimal at relatively high temperatures, slanting-enough temperature profiles, and relatively near (the incident wavelength) receiving spectral intervals. Then, both above-mention approaches can be used to obtain the undistorted temperature and convolved density profiles. Under general conditions, deconvolution procedures are necessary for improving the recovery accuracy and resolution. The analytical conclusions deduced in the work are supported by numerical results.