Heating and current drive in STEP: why neutral beam injection is not desirable
Spherical Tokamak for Energy Production (STEP) is the UK’s prototype fusion power plant programme aiming to demonstrate net electrical output from a spherical tokamak. The plasma scenarios require a completely non-inductive current drive for the flat-top and the majority of the ramp-up/down phases....
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| Format: | Article |
| Language: | English |
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IOP Publishing
2025-01-01
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| Series: | Nuclear Fusion |
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| Online Access: | https://doi.org/10.1088/1741-4326/add4ef |
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| author | Thomas Wilson Mark Henderson Hana El-Haroun Anurag Saigiridhari Emmi Tholerus |
| author_facet | Thomas Wilson Mark Henderson Hana El-Haroun Anurag Saigiridhari Emmi Tholerus |
| author_sort | Thomas Wilson |
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| description | Spherical Tokamak for Energy Production (STEP) is the UK’s prototype fusion power plant programme aiming to demonstrate net electrical output from a spherical tokamak. The plasma scenarios require a completely non-inductive current drive for the flat-top and the majority of the ramp-up/down phases. Most of the current ( $\sim {80}\% $ ) is self-generated by the plasma pressure gradient with the remainder provided by the heating and current drive (HCD) system. The capabilities and limitations of neutral beam injection (NBI) for current drive in relevant STEP scenarios are presented alongside a discussion of integration challenges. It is demonstrated that, in isolation, NBI has excellent current drive efficiency achieving $\zeta = 0.4$ at $\rho = 0$ rising to $\zeta = 1.4$ at $\rho = 0.8$ for beam energies $ \unicode{x2A7D} 1{\text{MeV}}$ . NBI current drive in STs also demonstrates a strong up-down asymmetry and weak dependence on the effective charge. However, once considered in an integrated design, the poor wall-plug efficiency, large size and consequent high cost make NBI undesirable in STEP compared to microwave based HCD. |
| format | Article |
| id | doaj-art-ac04fe2a2ac44b10b076bd3891998d3c |
| institution | Kabale University |
| issn | 0029-5515 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | Nuclear Fusion |
| spelling | doaj-art-ac04fe2a2ac44b10b076bd3891998d3c2025-08-20T03:49:37ZengIOP PublishingNuclear Fusion0029-55152025-01-0165606602010.1088/1741-4326/add4efHeating and current drive in STEP: why neutral beam injection is not desirableThomas Wilson0https://orcid.org/0009-0001-4343-834XMark Henderson1https://orcid.org/0000-0003-0144-3498Hana El-Haroun2https://orcid.org/0009-0005-6682-9596Anurag Saigiridhari3https://orcid.org/0009-0001-8656-8072Emmi Tholerus4https://orcid.org/0000-0002-3262-1958UKAEA, Culham Campus , Abingdon OX14 3DB, United Kingdom of Great Britain and Northern IrelandUKAEA, Culham Campus , Abingdon OX14 3DB, United Kingdom of Great Britain and Northern IrelandUKAEA, Culham Campus , Abingdon OX14 3DB, United Kingdom of Great Britain and Northern IrelandUKAEA, Culham Campus , Abingdon OX14 3DB, United Kingdom of Great Britain and Northern IrelandUKAEA, Culham Campus , Abingdon OX14 3DB, United Kingdom of Great Britain and Northern IrelandSpherical Tokamak for Energy Production (STEP) is the UK’s prototype fusion power plant programme aiming to demonstrate net electrical output from a spherical tokamak. The plasma scenarios require a completely non-inductive current drive for the flat-top and the majority of the ramp-up/down phases. Most of the current ( $\sim {80}\% $ ) is self-generated by the plasma pressure gradient with the remainder provided by the heating and current drive (HCD) system. The capabilities and limitations of neutral beam injection (NBI) for current drive in relevant STEP scenarios are presented alongside a discussion of integration challenges. It is demonstrated that, in isolation, NBI has excellent current drive efficiency achieving $\zeta = 0.4$ at $\rho = 0$ rising to $\zeta = 1.4$ at $\rho = 0.8$ for beam energies $ \unicode{x2A7D} 1{\text{MeV}}$ . NBI current drive in STs also demonstrates a strong up-down asymmetry and weak dependence on the effective charge. However, once considered in an integrated design, the poor wall-plug efficiency, large size and consequent high cost make NBI undesirable in STEP compared to microwave based HCD.https://doi.org/10.1088/1741-4326/add4efneutral beamheating and current drivespherical tokamakfusion power plant |
| spellingShingle | Thomas Wilson Mark Henderson Hana El-Haroun Anurag Saigiridhari Emmi Tholerus Heating and current drive in STEP: why neutral beam injection is not desirable Nuclear Fusion neutral beam heating and current drive spherical tokamak fusion power plant |
| title | Heating and current drive in STEP: why neutral beam injection is not desirable |
| title_full | Heating and current drive in STEP: why neutral beam injection is not desirable |
| title_fullStr | Heating and current drive in STEP: why neutral beam injection is not desirable |
| title_full_unstemmed | Heating and current drive in STEP: why neutral beam injection is not desirable |
| title_short | Heating and current drive in STEP: why neutral beam injection is not desirable |
| title_sort | heating and current drive in step why neutral beam injection is not desirable |
| topic | neutral beam heating and current drive spherical tokamak fusion power plant |
| url | https://doi.org/10.1088/1741-4326/add4ef |
| work_keys_str_mv | AT thomaswilson heatingandcurrentdriveinstepwhyneutralbeaminjectionisnotdesirable AT markhenderson heatingandcurrentdriveinstepwhyneutralbeaminjectionisnotdesirable AT hanaelharoun heatingandcurrentdriveinstepwhyneutralbeaminjectionisnotdesirable AT anuragsaigiridhari heatingandcurrentdriveinstepwhyneutralbeaminjectionisnotdesirable AT emmitholerus heatingandcurrentdriveinstepwhyneutralbeaminjectionisnotdesirable |