Electron Density Calculation Based On Stark Broadening Of D Balmer Line From Detached Plasma In EAST Divertor

In order to ensure a sufficient lifetime of the divertor material for future fusion devices such as ITER,it is important to operate the fusion devices with at least partial detachment.Recently,the change in magnetic topology caused by LHW-induced(Low Hybrid Wave)filament currents results in the splitting of the particle and heat flux on the divertor,which plays a key role in reducing the peak heat flux and erosion at the main strike point,thus facilitating long-pulse operations.Understanding of the detachment process with LHW-induced particle and heat flux striations is a prerequisite to achieving well-controlled detachment in a long pulse operation.The high electron density(ne)region is retracted from the target,the Langmuir probes(LPs)embedded in the target do not provide useful information about the plasma in the divertor volume.In order to understand the dominant physical mechanisms that govern detachment,it is important to acquire effective plasma parameters to constrain theoretical models.The analysis of the Stark shift and the broadening of the spectra is one of the most important techniques of plasma diagnostics,especially for determining plasma electron densities.The analyzation of emitting spectrum from detachment plasma in divertor of the Experimental Advanced Superconducting Tokamak(EAST)was done in this thesis.The full-width at half-maximum(FWHM)of Stark broadening can be obtained by deconvoluting the instrument broadening and the Doppler broadening.Then one can calculate the ne distribution and evolution using the quasi-static approximation.Two electron density bands are observed in the detached divertor plasma during an L-mode discharge sustained by Low Hybrid Wave(LHW)heating.With the increasing of the central line-averaged density,the SB density presents different characteristics at the two bands.First,a rise followed by a continous drop is observed at the upper band corresponding to the outer strike point,while the lower density band corresponding to striated particle flux presents a continual rise although its electron density is two times of the electron density corresponding to the outer strike point.In the detached outer divertor,the ne from the SB calculation is over one order of magnitude higher than that from the LP in both density bands.The densities from LPs in both bands keep decreasing with the increasing of the central line-averaged density,which could reflect the fact that the highest ne region moving into the divertor volume after being retracted from the target.The electron density is obtained by fitting the theoretical spectrum from the micro-field model method to the measured D? data using a least squares method.Compared with the electron density from the quasi-static approximation,the biggest discrepancy is 17.4%in the considered density range(5 × 1019-3 × 1020 m-3),while the discrepancy shrinks at lower density,such as,the discrepancy is almost 0 at 5 × 1019 m-3.The study shows that the calculation of the ne distribution and evolution based on the Stark broadening of the D? line provides an effective diagnostic to understand the detachment in EAST tokamak.In general,the quasi-static approximation is valid in most detachment,while the micro-field model method can provide more precise results when the ne is higher than 3 × 1020 m-3.