Divertor plasma opacity effects
In high recycling and detached plasma regimes the recycling region largely defines the properties of the whole scrape-off layer plasma by setting up the density and temperature profiles. As detachment approaches, the plasma temperature in the vicinity of the divertor targets drops to Te ∼ 1 eV and d...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2023-03-01
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| Series: | Nuclear Materials and Energy |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S235217912200223X |
| _version_ | 1811154372134961152 |
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| author | A.A. Pshenov A.S. Kukushkin A.V. Gorbunov E.D. Marenkov |
| author_facet | A.A. Pshenov A.S. Kukushkin A.V. Gorbunov E.D. Marenkov |
| author_sort | A.A. Pshenov |
| collection | DOAJ |
| description | In high recycling and detached plasma regimes the recycling region largely defines the properties of the whole scrape-off layer plasma by setting up the density and temperature profiles. As detachment approaches, the plasma temperature in the vicinity of the divertor targets drops to Te ∼ 1 eV and density increases to ne ∼ 1020–21 m−3, and the recycling region becomes increasingly opaque to the hydrogen radiation. Hydrogen radiation trapping influences both power and particle balance, both directly – reducing hydrogen radiation loss and changing plasma ionization/recombination balance inside the recycling region, and indirectly – affecting impurity radiation, charge-exchange and other important processes through the changes in the edge plasma density and temperature profiles.This paper reviews three-decade-long experimental and simulation efforts of quantifying the effects of hydrogen radiation trapping on the tokamak divertor plasma. It is demonstrated that opacity has a strong impact on the local divertor plasma parameters, changing both the electron and atomic hydrogen densities by a factor of several compared to the transparent plasma limit. Moreover, it is shown that allowing for opacity shifts the operational window of tokamak divertor towards higher separatrix densities and higher impurity content in order to maintain the desired level of power dissipation within the divertor. However, the most important is the effect of the opacity on the spectroscopic diagnostics. It is shown that despite the divertor plasma is virtually always transparent to the Balmer series emission, the resulting signals are affected by the changes in the populations of the excited states of atomic hydrogen, associated with the Lyman series absorption. As a result, the intensity of individual Balmer series signals can increase by a factor of 4 – 8 and the ratios of the Balmer line signals change by a factor of 2. This result implies that reliable quantitative measurements of plasma parameters with spectroscopic diagnostics at high power, high density tokamaks require opacity strength measurements and corresponding corrections to the rate coefficients used for the analysis of the spectroscopic data. |
| first_indexed | 2024-04-10T04:14:28Z |
| format | Article |
| id | doaj.art-0394ab1f83c9477399de2441397be33c |
| institution | Directory Open Access Journal |
| issn | 2352-1791 |
| language | English |
| last_indexed | 2024-04-10T04:14:28Z |
| publishDate | 2023-03-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Nuclear Materials and Energy |
| spelling | doaj.art-0394ab1f83c9477399de2441397be33c2023-03-12T04:21:22ZengElsevierNuclear Materials and Energy2352-17912023-03-0134101342Divertor plasma opacity effectsA.A. Pshenov0A.S. Kukushkin1A.V. Gorbunov2E.D. Marenkov3NRC “Kurchatov Institute”, Moscow, Russian Federation; National Research Nuclear University MEPhI, Moscow, Russian Federation; Corresponding author at: NRC “Kurchatov Institute”, Moscow, Russian Federation.NRC “Kurchatov Institute”, Moscow, Russian Federation; National Research Nuclear University MEPhI, Moscow, Russian FederationNRC “Kurchatov Institute”, Moscow, Russian FederationNational Research Nuclear University MEPhI, Moscow, Russian FederationIn high recycling and detached plasma regimes the recycling region largely defines the properties of the whole scrape-off layer plasma by setting up the density and temperature profiles. As detachment approaches, the plasma temperature in the vicinity of the divertor targets drops to Te ∼ 1 eV and density increases to ne ∼ 1020–21 m−3, and the recycling region becomes increasingly opaque to the hydrogen radiation. Hydrogen radiation trapping influences both power and particle balance, both directly – reducing hydrogen radiation loss and changing plasma ionization/recombination balance inside the recycling region, and indirectly – affecting impurity radiation, charge-exchange and other important processes through the changes in the edge plasma density and temperature profiles.This paper reviews three-decade-long experimental and simulation efforts of quantifying the effects of hydrogen radiation trapping on the tokamak divertor plasma. It is demonstrated that opacity has a strong impact on the local divertor plasma parameters, changing both the electron and atomic hydrogen densities by a factor of several compared to the transparent plasma limit. Moreover, it is shown that allowing for opacity shifts the operational window of tokamak divertor towards higher separatrix densities and higher impurity content in order to maintain the desired level of power dissipation within the divertor. However, the most important is the effect of the opacity on the spectroscopic diagnostics. It is shown that despite the divertor plasma is virtually always transparent to the Balmer series emission, the resulting signals are affected by the changes in the populations of the excited states of atomic hydrogen, associated with the Lyman series absorption. As a result, the intensity of individual Balmer series signals can increase by a factor of 4 – 8 and the ratios of the Balmer line signals change by a factor of 2. This result implies that reliable quantitative measurements of plasma parameters with spectroscopic diagnostics at high power, high density tokamaks require opacity strength measurements and corresponding corrections to the rate coefficients used for the analysis of the spectroscopic data.http://www.sciencedirect.com/science/article/pii/S235217912200223XTokamakDivertorRadiation transportDetachment |
| spellingShingle | A.A. Pshenov A.S. Kukushkin A.V. Gorbunov E.D. Marenkov Divertor plasma opacity effects Nuclear Materials and Energy Tokamak Divertor Radiation transport Detachment |
| title | Divertor plasma opacity effects |
| title_full | Divertor plasma opacity effects |
| title_fullStr | Divertor plasma opacity effects |
| title_full_unstemmed | Divertor plasma opacity effects |
| title_short | Divertor plasma opacity effects |
| title_sort | divertor plasma opacity effects |
| topic | Tokamak Divertor Radiation transport Detachment |
| url | http://www.sciencedirect.com/science/article/pii/S235217912200223X |
| work_keys_str_mv | AT aapshenov divertorplasmaopacityeffects AT askukushkin divertorplasmaopacityeffects AT avgorbunov divertorplasmaopacityeffects AT edmarenkov divertorplasmaopacityeffects |