Theoretical Studies On Electron-impact Excitation Processes And The Corresponding Polarizations Of Radiative Lines Of Highly Charged Tungsten Ions

Tungsten, because of its high melting point, low sputtering rate and retention oftritium，is the leading candidate plasma-facing material within the divertor region ofthe International Thermonuclear Experimental Reactor （ITER） tokamak. Although ithas above favorable characteristics, tungsten particles will still sputter of the surfacesand get into the divertor region plasma.These tungsten ions will be in various excitedstates by collisions with other particles and then decay radiatively by producing agreat number of line radiations over a wide range of energies, these line radiations canalso be used as diagnostic probes reflecting information about fusion plasmas. andlinear degree of polarization is a significant one. The existing works show linearpolarizations of X-rays can reveal important information about various physicaleffects and population mechanisms of levels. However, to our best knowledge, thereare very few works on the degree of linear polarization for tungsten X-ray spectra inthe relevant spectral region of the ITER fusion plasmas.In the present work, the cross sections for electron-impact excitation toindividual magnetic sublevels of tungsten ions are calculated by using a newlydeveloped fully relativistic distorted-wave （RDW） program REIE06, which are usedto study the electron-impact excitation （EIE） and dielectronic recombination （DR）processes, respectively. The target state wave functions are generated with the use ofthe atomic structure package GRASP92based on the multiconfiguration Dirac-Fock（MCDF） method, and the continuum electron wave functions are produced by thecomponent COWF of the Ratip package. In this thesis, a brief introduction aboutsome basic concepts and research background of this work has been given in chapter1. And chapter2described the MCDF method and the method of RDW. In chapter3,the2s_1/2-2p_3/2excitation in W⁶⁵⁺through W⁷¹⁺ions as well as the polarization ofresulting transitional lines are calculated, with the utilization of a fully relativisticdistorted-wave（RDW） method. Based on the calculation, the behaviors of theexcitation cross sections and polarization with increasing of incident electron energyare discussed systematically. In chapter4, cross sections for EIE and capture tospecific magnetic sublevels of W⁴⁶⁺to W⁴²⁺ions have been calculated by using a fullyrelativistic distorted-wave （RDW） method. And the degrees of linear polarization for the corresponding strongest nf→3d （n=4,5,6） transition lines formed by both theEIE and DR processes are also computed, respectively, It is also found that thedifferences of linear polarization from both the EIE and DR processes are very large.This feature can reveal the polarizations of the lines are from the different formationmechanisms. It is expected that the obvious differences between the polarizations canbe used to distinguish the formation mechanism of the corresponding lines. someconclusions and prospects of future work have been given in chapter5.