Research Of Reconstruction Of The Spatial Distribution Of Electron Density In Tokamaks

Methods to reconstruct electron density spatial distribution are studied and researched, and the methods are used in HT-7 tokamak. A new method to reconstruct plasma density distribution based on the plasma shapes is proposed on the basic of the theory of plasma physics, this method will be applicable to EAST (Experimental Advanced Superconducting Tokamak) and other non-circular fusion devices.The dataset of the electron density in tokamak are often obtained by HCN or DCN laser interferometers of electromagnetic waves. There used to be big noises in the integral signals obtained by the measurements. We studied the original signal processing algorithm and gave an improved one which can eliminate baseline offset accurately and process the signal overturning effectively. With the wavelet analysis method to denoise HCN signal, high accuracy and low noise HCN signal is obtained. Using good HCN signal can reconstruct the spatial distribution of electron density more accurately.Various problems to reconstruct local intensity distribution of some physical quantity from its line integrals along observation paths are reduced to the first kind integral equation. Many algorithms have been proposed and studied because of the importance of the problem. Abel inversion is used popularly, though this method seems very general, the method strongly depends on the symmetry of the system and this method should be applied carefully when the system is not symmetric in the direction of the integration paths. It is often the case that, in a practical situation, a reconstructed image is unsymmetrical on a plane, furthermore, the plasma shapes are more complicated because divertors are widely used in modern fusion devices, new methods must be developed to be used in strongly unsymmetrical systems.The contours of plasma shape can be considered as the contours of electronic density under equilibrium. So we propose the new method realized by making use of the plasma shapes obtained from EFIT(Equilibrium Fitting code). The reconstructed results of the density spatial distribution in HT-7 tokamak are demonstrated in the paper. We expect the method can be used in EAST, however, there is only one channel laser interferometer in EAST now. We will reconstruct the density distribution and use it in density feedback control in EAST in the near future.