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Relativistic calculations of electron impact excitation cross-sections of neutral tungsten

Ritu Dey, Ayushi Agarwal, Reetesh Kumar Gangwar, Deepti Sharma, M. B. Chowdhuri, Rajesh Srivastava, Joydeep Ghosh

Abstract

Reliable tungsten spectroscopy is essential for modelling and diagnosing tungsten-containing plasmas, particularly in edge/divertor conditions where neutral tungsten (WI) is produced by sputtering and contributes to visible/near-UV emission. In this work, we present fine-structure-resolved EIE cross sections for W I computed using the relativistic distorted-wave (RDW) method. Target states are described by multi-configurational Dirac-Fock (MCDF)wave functions with an extensive configuration-interaction (CI) expansion including valence-valence and core-valence correlation through hole and deeper-core configurations. The resulting energies are bench marked against available theoretical results and the recommended values from the NIST database. Fine-structure-resolved cross sections are reported for excitations from the ground level 5d4 6s2 (5 D0) and six metastable levels 5d4 6s2 (5D1 , 5D2 , 5D3, 5D4 , 3P0) and 5d5 (6S)6s (7S3 ) into excited levels belonging primarily to the 5d4 6s(6 D)6p and 5d5 (6S)6p configurations, over incident electron energies from threshold to 500 eV. With the exception of a limited set of previously studied transitions, most of the reported fine-structure-resolved cross sections are presented here for the first time. The results show a strong dependence on the initial level and indicate that excitation from the metastable state yields the largest cross sections among the states considered, highlighting the importance of metastable populations in W I modelling. In addition, radiative transition probabilities for selected prominent transitions are calculated and compared with existing data. The present dataset is expected to be valuable for collisional-radiative modelling and spectroscopic diagnostics of tungsten plasmas in the 1-50 eV range.

Relativistic calculations of electron impact excitation cross-sections of neutral tungsten

Abstract

Reliable tungsten spectroscopy is essential for modelling and diagnosing tungsten-containing plasmas, particularly in edge/divertor conditions where neutral tungsten (WI) is produced by sputtering and contributes to visible/near-UV emission. In this work, we present fine-structure-resolved EIE cross sections for W I computed using the relativistic distorted-wave (RDW) method. Target states are described by multi-configurational Dirac-Fock (MCDF)wave functions with an extensive configuration-interaction (CI) expansion including valence-valence and core-valence correlation through hole and deeper-core configurations. The resulting energies are bench marked against available theoretical results and the recommended values from the NIST database. Fine-structure-resolved cross sections are reported for excitations from the ground level 5d4 6s2 (5 D0) and six metastable levels 5d4 6s2 (5D1 , 5D2 , 5D3, 5D4 , 3P0) and 5d5 (6S)6s (7S3 ) into excited levels belonging primarily to the 5d4 6s(6 D)6p and 5d5 (6S)6p configurations, over incident electron energies from threshold to 500 eV. With the exception of a limited set of previously studied transitions, most of the reported fine-structure-resolved cross sections are presented here for the first time. The results show a strong dependence on the initial level and indicate that excitation from the metastable state yields the largest cross sections among the states considered, highlighting the importance of metastable populations in W I modelling. In addition, radiative transition probabilities for selected prominent transitions are calculated and compared with existing data. The present dataset is expected to be valuable for collisional-radiative modelling and spectroscopic diagnostics of tungsten plasmas in the 1-50 eV range.
Paper Structure (12 sections, 6 equations, 8 figures, 2 tables)

This paper contains 12 sections, 6 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Theory
  3. Results and Discussions:
  4. Excitation from the Ground State ($5d^46s^2,{}^5D_0$)
  5. Excitation from the Metastable State $5d^46s^2,{}^5D_1$
  6. Excitation from the Metastable State $5d^5(^6S)6s,{}^7S_3$
  7. Excitation from the Metastable State $5d^46s^2,{}^5D_2$
  8. Excitation from the Metastable State $5d^46s^2,{}^5D_3$
  9. Excitation from the Metastable State $5d^46s^2,{}^5D_4$
  10. Excitation from the Metastable State $5d^46s^2,{}^3P_0$
  11. Conclusions
  12. Acknowledgements

Figures (8)

  • Figure 1: Electron impact excitation cross-sections of W I from ground state 5d$^4$6s$^2$ ($^5$D$_0$) to various excited states (a-d).
  • Figure 2: Electron impact excitation cross-sections of W I from metastable state 5d$^4$6s$^2$ ($^5$D$_1$) to various excited states (a-d), respectively.
  • Figure 3: Electron impact excitation cross-sections of W I from metastable state 5d$^5$6s ($^7$S$_3$) to various excited states (a-d).
  • Figure 4: Electron impact excitation cross-sections of W I from metastable state 5d$^4$6s$^2$ ($^5$D$_2$) to various excited states (a-d).
  • Figure 5: Electron impact excitation cross-sections of W I from metastable state 5d$^4$6s$^2$ ($^5$D$_3$) to various excited states (a-d).
  • ...and 3 more figures