Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI
Extrinsic impurity seeding is planned for ITER to avoid high heat fluxes to the tungsten divertor targets. Nevertheless, excessive sputtering by impurities would lead to a reduction in fusion power output and divertor lifetime. Unlike today’s fusion devices, the entrainment of impurities is expected...
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IOP Publishing
2024-01-01
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| Online Access: | https://doi.org/10.1088/1741-4326/ad97ca |
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| author | Mark J.H. Cornelissen Jordy W.M. Vernimmen Jesse D.E. Verstappen Erwin Zoethout Ivo G.J. Classen Job Beckers Thomas W. Morgan |
| author_facet | Mark J.H. Cornelissen Jordy W.M. Vernimmen Jesse D.E. Verstappen Erwin Zoethout Ivo G.J. Classen Job Beckers Thomas W. Morgan |
| author_sort | Mark J.H. Cornelissen |
| collection | DOAJ |
| description | Extrinsic impurity seeding is planned for ITER to avoid high heat fluxes to the tungsten divertor targets. Nevertheless, excessive sputtering by impurities would lead to a reduction in fusion power output and divertor lifetime. Unlike today’s fusion devices, the entrainment of impurities is expected to play an increasing role in ITER’s highly collisional near-surface plasma. Impurity entrainment refers to the acceleration of impurities with the plasma flow by collisional drag, leading to elevated impact energies. To investigate impurity entrainment under ITER-like divertor plasma conditions ( $n_{\mathrm{e}} \gt 2 \times 10^{20}$ m ^−3 , $T_{\mathrm{e}} \lt $ 5 eV), argon-seeded hydrogen plasmas were formed in the linear plasma generator Magnum-PSI. Doppler shifts in spatially-resolved emission profiles of argon (Ar II - 480.6 nm) and hydrogen (H $_\mathrm{\beta}$ - 486.1 nm) reveal the entrainment of seeded argon towards the upstream hydrogen velocity (∼9 cm from the surface), corresponding to ∼0.39 of the common-system sound speed. In addition, the sputtering yield of tungsten by argon bombardment for the argon-seeded hydrogen plasma was compared to a pure argon plasma by monitoring tungsten (W I - 400.9 nm) emission. These sputtering experiments reveal further entrainment of the argon impurities to ∼0.65 of the common-system sound speed at the sheath edge, leading to a large increase in their impact energy. Extrapolation of the Magnum-PSI results to ITER, using existing SOLPS-ITER simulations to determine the divertor plasma conditions, indicates more than an order of magnitude increase in gross erosion of the divertor targets due to impurity entrainment. However, the net erosion rate could still be kept under control if high re-deposition rates are achieved, which is treated in the companion paper (Cornelissen M.J.H. et al 2025 Nucl. Fusion 65 026008). The combination of a low sputtering threshold energy and high impact energy of impurities constrains the fine balance between radiative cooling with impurity seeding and avoiding extensive divertor erosion. |
| format | Article |
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| spelling | doaj-art-20257ff73ad8428b9895da2bb05436e92025-08-20T01:59:53ZengIOP PublishingNuclear Fusion0029-55152024-01-0165202600910.1088/1741-4326/ad97caErosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSIMark J.H. Cornelissen0https://orcid.org/0000-0001-7576-4628Jordy W.M. Vernimmen1https://orcid.org/0000-0003-2698-7459Jesse D.E. Verstappen2Erwin Zoethout3https://orcid.org/0000-0002-9012-6859Ivo G.J. Classen4https://orcid.org/0000-0001-8982-8856Job Beckers5https://orcid.org/0000-0001-6116-7013Thomas W. Morgan6https://orcid.org/0000-0002-5066-015XDepartment of Applied Physics, Eindhoven University of Technology , P.O. Box 513, Eindhoven, 5600 MB, Netherlands; DIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsDIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsDepartment of Applied Physics, Eindhoven University of Technology , P.O. Box 513, Eindhoven, 5600 MB, Netherlands; DIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsDIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsDIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsDepartment of Applied Physics, Eindhoven University of Technology , P.O. Box 513, Eindhoven, 5600 MB, NetherlandsDepartment of Applied Physics, Eindhoven University of Technology , P.O. Box 513, Eindhoven, 5600 MB, Netherlands; DIFFER—Dutch Institute for Fundamental Energy Research , De Zaale 20, Eindhoven, 5612 AJ, NetherlandsExtrinsic impurity seeding is planned for ITER to avoid high heat fluxes to the tungsten divertor targets. Nevertheless, excessive sputtering by impurities would lead to a reduction in fusion power output and divertor lifetime. Unlike today’s fusion devices, the entrainment of impurities is expected to play an increasing role in ITER’s highly collisional near-surface plasma. Impurity entrainment refers to the acceleration of impurities with the plasma flow by collisional drag, leading to elevated impact energies. To investigate impurity entrainment under ITER-like divertor plasma conditions ( $n_{\mathrm{e}} \gt 2 \times 10^{20}$ m ^−3 , $T_{\mathrm{e}} \lt $ 5 eV), argon-seeded hydrogen plasmas were formed in the linear plasma generator Magnum-PSI. Doppler shifts in spatially-resolved emission profiles of argon (Ar II - 480.6 nm) and hydrogen (H $_\mathrm{\beta}$ - 486.1 nm) reveal the entrainment of seeded argon towards the upstream hydrogen velocity (∼9 cm from the surface), corresponding to ∼0.39 of the common-system sound speed. In addition, the sputtering yield of tungsten by argon bombardment for the argon-seeded hydrogen plasma was compared to a pure argon plasma by monitoring tungsten (W I - 400.9 nm) emission. These sputtering experiments reveal further entrainment of the argon impurities to ∼0.65 of the common-system sound speed at the sheath edge, leading to a large increase in their impact energy. Extrapolation of the Magnum-PSI results to ITER, using existing SOLPS-ITER simulations to determine the divertor plasma conditions, indicates more than an order of magnitude increase in gross erosion of the divertor targets due to impurity entrainment. However, the net erosion rate could still be kept under control if high re-deposition rates are achieved, which is treated in the companion paper (Cornelissen M.J.H. et al 2025 Nucl. Fusion 65 026008). The combination of a low sputtering threshold energy and high impact energy of impurities constrains the fine balance between radiative cooling with impurity seeding and avoiding extensive divertor erosion.https://doi.org/10.1088/1741-4326/ad97caentrainmenterosiontungstenimpuritiesspectroscopyMagnum-PSI |
| spellingShingle | Mark J.H. Cornelissen Jordy W.M. Vernimmen Jesse D.E. Verstappen Erwin Zoethout Ivo G.J. Classen Job Beckers Thomas W. Morgan Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI Nuclear Fusion entrainment erosion tungsten impurities spectroscopy Magnum-PSI |
| title | Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI |
| title_full | Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI |
| title_fullStr | Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI |
| title_full_unstemmed | Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI |
| title_short | Erosion enhancement by impurity entrainment in the highly collisional plasmas of Magnum-PSI |
| title_sort | erosion enhancement by impurity entrainment in the highly collisional plasmas of magnum psi |
| topic | entrainment erosion tungsten impurities spectroscopy Magnum-PSI |
| url | https://doi.org/10.1088/1741-4326/ad97ca |
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