Optical Emission Spectroscopy Of Electron Temperature And Density In SUNIST

The atomic emission spectroscopy is one of the key diagnostics for tokamak plasmaresearch, and, therefore, to investigate the method of spectroscopy diagnostics is of greatimportance. The dissertation is devoted to develop a spectroscopy diagnostic method fordetermination of the electron temperature and density in helium plasmas and finally toestablish an spectroscopy diagnostics system in the SUNIST spherical tokamakInthedissertationacollisional-radiative(CR)modelisdevelopedforheliumplasmaswithin the parameter ranges of SUNIST helium discharging plasmas. The significance ofreaction rates of the number densities of helium excited states is evaluated for collisionswith electrons and heavy particles, then the equations of the collision-radiative atomicprocesses are established. Especially, the propagation of the uncertainties in the reactionratecoefficientsofatomicprocessesisanalyzedindetails. Throughtheanalysis, themax-imum principle quantum number of the excited states in the CR model can be determinedaccording to error in the model. For SUNIST helium plasmas, it is found that the CRmodel can give acceptable calculations when the maximum principle quantum number ofincluded excited states equals. Finally a line-ratio method is established by selectingappropriate line emissions for the helium discharges of SUNIST.On the hardware, an atomic emission spectroscopy system is constructed. The lineemissions of the plasmas are measured by a shot to shot method based on the repetition ofthe discharges. Then by employing the CR model we developed, the electron temperatureand density are obtained by the method of spectroscopy diagnostics. The diagnostic re-sults are confirmed to be trustable by comparing with those from other diagnostics, suchas the microwave interferometry. In additional, some other preliminary results of mea-sured line emission signals are found, such as the ratio of the measured electron densityby the line-ratio method to that by the microwave interferometry is closely related withthe spatial distribution of the plasma, and the intensities of line emissions have the sametime-frequency fluctuation behaviors with those of the signals measured by the magneticprobes.Some highlighted works in this dissertation include:1. An error propagation function has been deduced for evaluation of the influencesof the uncertainties of rate coefficients of the atomic processes on the calculated number densities of the excited states by the CR model. By using the error propagation function,one can raise a claim on the uncertainties of the atomic reaction rate coefficients directly,or, calculate the error of number densities of the excited states when the rates coefficientsare given in the CR model. This method is simple but has a clear physics meaning com-pared to the traditional method, by which the CR mode is re-solved with perturbed ratecoefficients. This error propagation function method developed in the dissertation is ex-pected to play an important role in the building and the evaluation of the CR model.2. A line-ratio method is established for diagnosing the electron temperature anddensity of plasma. Based on the method, electron temperature and density are obtained inthe helium plasma of SUNIST and the results have been confirmed to be trustable. Thisline-ratio method can provide reference for the diagnostics of plasmas those have thesimilar range of plasma parameters with SUNIST, such as core plasma in small tokamaksand edge/divertor plasma in large tokamaks.3. Some ideas for further research in the atomic emission spectroscopy field are pro-posed. The ratio of measured electron density by line-ratio method to that by microwaveinterferometry is closely related with the spatial distribution profile of the plasma. Thisfact will provide us a method to diagnose the density profile of the plasma. Anotherexperimental observation is that the signals of line emissions have the same fluctuationbehaviors with those measured by the magnetic probes, and it will provide us a possibilityof investigating the MHD behaviors in plasmas by optical spectroscopy diagnostics.