Collisional-radiative Model Of The M1 Transition Spectra For The W⁵³⁺ Ion

Tungsten has been selected as a divertor and wall material for magnetic confinement fusion reactors（e.g.ITER,EAST）due to its excellent physical properties such as high melting point,high sputtering energy threshold,low sputtering rate and low deuterium and tritium retention rate.Interaction between the tungsten facing component and the high temperature plasma in the magnetic confinement device generates impurity tungsten ions,which might be transported to the core plasma,where they are ionized into higher ionized tungsten ions.However,even in the core plasma,these tungsten ions can not be completely ionized,and these highly charged tungsten ions will spontaneously radiate high-energy photons,resulting in a decrease of the plasma temperature,which can directly lead to plasma quenching if the concentration of impurity tungsten ions is too large.Therefore,monitoring and controlling the flow of tungsten impurities is very important for the success of thermonuclear fusion.And the emission spectra of small amounts of impurity tungsten ions can help diagnose the plasma parameters such as the electron temperature and electron density.In order to monitor and control the tungsten impurity flow and to diagnose the plasma,the atomic structure,radiative properties and spectral information of various ionized tungsten ions need to be investigated in depth.In this paper,the fundamental atomic data of W⁵³⁺ions,such as energy level structure,radiative transition rates and collisional excitation cross sections,are calculated using the Flexible Atomic Code（FAC）package based on the relativistic configuration interaction（RCI）and the GRASP2K package based on the multi-configuration Dirac-Hartree-Fock（MCDHF）method,respectively.After that,a reasonable Collisional-Radiative model was constructed to simulate the M1transition spectra of W⁵³⁺ion observed in the Electron Beam Ion Trap（EBIT）,and a theoretical study of the M1 transition spectra in the range of 10-20 nm was carried out.The main contents including.1.Atomic data on the energy levels,radiative transition energy,transition rate and collisional excitation cross sections of W⁵³⁺ions have been calculated using the RCI and MCDHF methods,and the convergence of the excitation energies of the ground and excited states and the effects of QED effects and Breit interactions on the excitation energy calculations are analyzed.The current calculation results agree well with the experimental and other available theoretical calculations.The results obtained by the MCDHF method are found to be in better agreement with both experimental and theoretical calculations than those obtained by the RCI method.Therefore,the radiative transition data used in the next sections are those calculated using the MCDHF method.2.A reasonable Collisional-Radiative model was constructed by considering the spontaneous radiative transition,electron collisional excitation and electron collisional de-excitation processes.The M1 transition spectra in the 10-20 nm range of W⁵³⁺ion with the electron temperature of 5755 eV and the electron density of the10¹²cm^-3in the EBIT environment were simulated.The wavelengths of 12.360 nm,15.794 nm,16.042 nm,17.244 nm and 18.918 nm were confirmed to be from M1transition:(（3d_-²）₀（3d₊）_5/2)_5/2→（3d_-³）_3/2,(（3d_-）_3/2（3d₊²）₄)_11/2→(（3d_-²）₂（3d₊）_5/2)_9/2,(（3d_-²）₂（3d₊）_5/2)_1/2→（3d_-³）3/2,(（3d_-²）₂（3d₊）_5/2)_3/2→（3d_-³）3/2,(（3d_-²）₂（3d₊）_5/2)_5/2→（3d_-³）3/2.The transitions at wavelengths around 15.943 nm,17.127 nm and 19.342 nm in the simulations were analyzed further with the M1 transition observed and identified experimentally for the W⁵³⁺ion and for ions in the dissociated state near the W⁵³⁺ion,and it was found that the transition at 15.943 nm could be a superposition of the M1 transitions of W⁵³⁺ion and W⁵⁵⁺ion.3.The two transitions(（3d_-）_3/2（3d₊²）₄)_7/2→(（3d_-²）₂（3d₊）_5/2)_5/2,(（3d_-）_3/2（3d₊²）₄)_9/2→(（3d_-²）₂（3d₊）_5/2)_9/2at the wavelengths of 16.683 nm and 18.018 nm may be identified in later experimental observations.4.The population flux of some specific transitions were calculated to reveal the energy level population mechanism of the excited states of W⁵³⁺ion.