Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak

T. Onchi, H. Idei, M. Fukuyama, D. Ogata, R. Ashida, T. Kariya, A. Ejiri, K. Matsuzaki, Y. Osawa, Y. Peng, S. Kojima, O. Watanabe, M. Hasegawa, K. Nakamura, K. Kuroda, R. Ikezoe, T. Ido, K. Hanada, N. Bertelli, M. OnoA. Fukuyama

Research output: Contribution to journalArticlepeer-review

Abstract

The plasma current is ramped up primarily by a 28 GHz electron cyclotron wave (ECW) in the Q-shu University experiment Steady-State Spherical Tokamak (QUEST), with multiple harmonic resonance layers from the second to the fourth stay in the plasma core. A steering antenna comprising two quasi-optical mirrors enhances the power density of ECWs. The ECW beam is injected obliquely from the low-field side where the parallel refractive index is N ∥ = 0.75 at the second-harmonic resonance layer. Analysis of the resonance condition has found that energetic electrons moving forward along the magnetic field resonate more effectively than those moving backward. Such symmetry breaking is consistent with the results of the current ramp-up experiment. The peak plasma current reaches I p > 70 kA, constantly injecting a beam of radio frequency power of 100 kW. Ray-tracing by the TASK/WR code demonstrates that the power of the 28 GHz extraordinary mode is absorbed by energetic electrons via single-pass cyclotron absorption.

Original languageEnglish
Article number022505
JournalPhysics of Plasmas
Volume28
Issue number2
DOIs
Publication statusPublished - Feb 1 2021

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics

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