Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: I. Experimental analysis of the tube structure
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- Dynamics of multiple flux tubes in sawtoothing KSTAR plasmas heated by electron cyclotron waves: I. Experimental analysis of the tube structure
- Choe, Gyuenghyuen; Yun, Gunsu; Nam, Yoonbum; Lee, Woochang; Park, Hyeon Keo; Bierwage, Andreas; Domier, Calvin W.; Luhmann, N. C., Jr; Jeong, J.H.; Bae, Youngsoon
- Issue Date
- INT ATOMIC ENERGY AGENCY
- NUCLEAR FUSION, v.55, no.1, pp.1 - 7
- Multiple (two or more) flux tubes are commonly observed inside and/or near the q = 1 flux surface in KSTAR tokamak plasmas with localized electron cyclotron resonance heating and current drive (ECH/CD). Detailed 2D and quasi-3D images of the flux tubes obtained by an advanced imaging diagnostic system showed that the flux tubes are m/n = 1/1 field-aligned structures co-rotating around the magnetic axis. The flux tubes typically merge together and become like the internal kink mode of the usual sawtooth, which then collapses like a usual sawtooth crash. A systematic scan of ECH/CD beam position showed a strong correlation with the number of flux tubes. In the presence of multiple flux tubes close to the q = 1 surface, the radially outward heat transport was enhanced, which explains naturally temporal changes of electron temperature. We emphasize that the multiple flux tubes are a universal feature distinct from the internal kink instability and play a critical role in the control of sawteeth using ECH/CD.
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