Feasibility study of line integrated backward Thomson scattering measurement in nuclear fusion reactors

In order to control or suppress edge localized modes in nuclear fusion reactors, an accurate pedestal pressure profile measurement is necessary. A line integrated backward Thomson scattering measurement is an attractive method because of its long scattering length. Assuming that the first mirror is located far from the plasma to avoid degradation of the mirror due to erosion and impurity deposition, the measurement accuracies of density and temperature and pressure are estimated. For the target plasma, we adopt the pedestal profile with the shoulder density of 10¹⁹ - 10²⁰ m⁻³ and the dimensions of the JA DEMO reactor. The calculation results show that, the Poisson noise due to finite detected scattered photon number is much larger than that due to bremsstrahlung emission. In addition, noise is enhanced by reconstruction process. The resultant total noise levels of reconstructed density, temperature and pressure profiles are at most 1.5%, 3%, 3%, respectively in the steep gradient region, and this method is feasible in the reactor. (author)