Impact of off-axis beam and low-field side gas fuelling on safety factor, rotation and fast ions MAST-U

ORAL

Abstract

The off-axis beam in MAST-U is utilized to deposit heating power and current drive avoiding MHD instabilities, but is inherently less efficient than the on-axis beam. We performed a systematic scan in beam timing to validate the q profile evolution change from MSE due to the off-axis beam. As part of the TRANSP analysis, the effects of reduced resistivity and bootstrap current due to heating are distinguished from NBCD. Doppler back-scattering is used to perform rotation and turbulence measurements in the k⊥ρ~1.5-15 range [1,2], in low density on and off-axis beam heated plasmas showing stronger rotation towards the edge as expected. With the off-axis beam, fast ions are located closer to the edge neutrals and is thus more subject to the influence of low-field side gas fuelling, producing charge exchange losses as well as damping the ExB and/or toroidal rotation. Deliberate flooding of gas into the low-field side region resulted in a slowing of the rotation, enhancement of passive FIDA (a proxy for CX losses [3]), reduction in the neutron rate and lowering electron temperature. Such a loss may be a result of loss of heating power or degradation or thermal conductivity from a decreased ExB shearing rate, supported by theory.

[1] T. L. Rhodes et al RSI 93 113549 (2022)

[2] P. Shi et al JINST 18 C11022 (2023)

[3] P Ollus et al PPCF 66 025009 (2024)

*This material is based upon work supported by the US DoE [grant numbers DE-SC0019007, DE-SC0019005, DE-AC05-00OR22725] and the RCUK [grant number EP/T012250/1].

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Presenters

  • Clive Alvin Michael

    • University of California

Authors

  • Clive Alvin Michael

    • University of California

  • Ridhima Sharma

    • UKAEA

  • Sam Blackmore

    • UKAEA
    • UKAEA - United Kingdom Atomic Energy Authority

  • Terry L Rhodes

    • University of California, Los Angeles

  • Peng Shi

    • Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China

  • Neal A Crocker

    • University of California, Los Angeles

  • Patrik Ollus

    • Department of Applied Physics, Aalto University, PO Box 11100, 00076 AALTO, Finland

  • Omkar Myatra

    • UKAEA

  • Jack J Lovell

    • Oak Ridge National Laboratory

  • Chris Bowman

    • UK Atomic Energy Authority (UKAEA)

  • Rory Scannell

    • UKAEA - United Kingdom Atomic Energy Authority

  • Ken G McClements

    • United Kingdom Atomic Energy Authority

  • Bhavin S Patel

    • UKAEA - United Kingdom Atomic Energy Authority
    • UK Atomic Energy Authority

  • Rennan Morales

    • UKAEA

  • Quinn Pratt

    • University of California, Los Angeles

  • William A Peebles

    • University of California, Los Angeles

  • Roman Lanstov

    • UCLA

  • Ian Fitzgerald

    • UKAEA

  • Zhongbing Shi

    • Southwestern Institute of Physics