Role of fast-ion transport manipulating safety factor profile in KSTAR early diverting discharges

J. Kang, T. Rhee, J. Kim, M. Podestà, L. Bardóczi, R. Nazikian, C. Z. Cheng, G. J. Kramer, M. J. Choi, S. H. Hahn, H. Han, M. H. Woo, H. Jhang, J. M. Park, J. M. Kwon

Research output: Contribution to journalArticlepeer-review

Abstract

Magnetohydrodynamics (MHD) activity is analyzed for a particular KSTAR discharge category, the main features of which are a high-qmin and a broad q profile. An interesting finding in this scenario is that a steady-state high-qmin and broad q profile has been constructed even without a strong off-axis current drive scheme. Time traces of magnetics spectrograms and electron cyclotron emission imaging (ECEI) clearly show that Alfvénic type MHD activity appears as a high-qmin and broad q profile is formed. Conversely, this activity disappears as the current profiles evolve toward a low-qmin profile. In this study, the effect of MHD modes and accompanying fast-particle transport on the formation of various current profiles is explored. The frequency patterns of the magnetics spectrograms and ECEI coherence are compared using a NOVA analysis to determine which series of Alfvénic modes are active. Then, the kick-model is applied to potential modes, and used to estimate how much fast-ions are transported and beam driven current profiles are varied. By comparing the reconstructed total current profile from the kinetic EFIT with the beam-driven current profile estimated from the kick model, it is determined how energetic particle transport is responsible for maintaining the safety factor profile and which q profile can provide high βN operation.

Original languageEnglish
Article number126023
JournalNuclear Fusion
Volume60
Issue number12
DOIs
Publication statusPublished - 2020 Dec

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

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