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Improvements to the High-Field-Side Transient CHI System on QUEST

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Abstract

Transient coaxial helicity injection (CHI) is a promising candidate for solenoid-free plasma current start-up in a low-aspect-ratio tokamak in support of developing fully non-inductive scenarios. The aim of the transient CHI research on QUEST is to develop a reactor-relevant CHI design. On QUEST, a CHI discharge is initiated by driving current along magnetic field lines that connect an electrically insulated electrode plate (which is referred to as a bias electrode) to a vessel component at the bottom region of the spherical tokamak. In the first application of CHI on QUEST, the electrically insulated electrode plate was biased with respect to the outer vessel in a configuration referred to as low-field-side (LFS) injection. To maintain a narrow injector flux footprint width throughout the discharge, QUEST is now developing a high-field-side (HFS) injection configuration, in which the electrically insulated electrode plate is biased with respect to the inner vessel components. Through the implementation of a CHI-dedicated gas injection system, studies in the HFS injection configuration have now demonstrated good magnetic flux evolution into the vacuum vessel. Toroidal currents up to 43 kA have been achieved, and the generated current has increased in proportion to the magnetic flux connecting the electrodes. These results which show agreement with the CHI-scaling suggest that much higher levels of toroidal current can be generated on QUEST in an optimized CHI system in which the magnetic flux connecting the CHI electrodes is further increased.

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Acknowledgements

This work is supported by US DOE grants (DE-SC0019415, and DE-AC02-09CH11466), NIFS Collaboration Research Program (NIFS17KUTR130 and NIFS19KUTR137), the Collaborative Research Program of Research Institute for Applied Mechanics, Kyushu University (International Collaboration Frame-work 18 NU-1 and 19 NU-1 and early career scientists support work), and a Grant-in-Aid for JSPS Fellows (KAKENHI Grant No. 19K14685). This work was partially supported by a Grant-in-Aid for JSPS Fellows (KAKENHI Grant No. 17H06089), the NIFS Collaboration Research Program (NIFS19KUTR136 and NIFS13KUTR085), and Japan/US Cooperation in Fusion Research and Development.

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Authors and Affiliations

  1. Research Institute for Applied Mechanics, Kyushu University, 816-8580, Kasuga, Japan

    K. Kuroda, M. Hasegawa, T. Onchi, K. Hanada, R. Ikezoe, H. Idei, T. Ido, S. Kawasaki, T. Nagata, A. Higashijima, S. Shimabukuro, I. Niiya, I. Sekiya & K. Nakamura

  2. University of Washington, Seattle, WA, USA

    R. Raman, B. A. Nelson & J. Rogers

  3. Princeton Plasma Physics Laboratory, 451, Princeton, NJ, 08543, USA

    M. Ono

  4. Institute for Advanced Fusion and Physics Education, Kumamoto, Japan

    O. Mitarai

  5. Graduate School of Engineering, University of Hyogo, Himeji, Japan

    M. Nagata

  6. National Institutes for Quantum Science and Technology, Naka, Japan

    S. Kojima

  7. Tokamak Energy Ltd, OX14 4SD, Milton Park, Abingdon, UK

    Y. Takase

  8. Department of Nuclear Engineering, Kyoto University, Kyoto, Japan

    S. Murakami

Authors
  1. K. Kuroda
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  2. R. Raman
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  3. M. Hasegawa
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  4. T. Onchi
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  5. K. Hanada
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  6. M. Ono
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  7. B. A. Nelson
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  8. J. Rogers
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  9. R. Ikezoe
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  15. T. Nagata
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  16. A. Higashijima
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  18. I. Niiya
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  19. I. Sekiya
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  20. S. Kojima
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  21. K. Nakamura
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  22. Y. Takase
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  23. S. Murakami
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Correspondence to K. Kuroda.

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Kuroda, K., Raman, R., Hasegawa, M. et al. Improvements to the High-Field-Side Transient CHI System on QUEST. J Fusion Energ 41, 25 (2022). https://doi.org/10.1007/s10894-022-00338-4

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  • DOI: https://doi.org/10.1007/s10894-022-00338-4

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