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ICRF Heating and Ion Tail Formation in LHD

K. Saito, R. Kumazawa, T. Seki, H. Kasahara, M. Osakabe, M. Isobe, F. Shimpo, G. Nomura, T. Watari, S. Murakami, M. Sasao, T. Mutoh, LHD Experiment Group

Fusion Science and Technology / Volume 58 / Number 1 / July-August 2010 / Pages 515-523

Chapter 10. Ion Cyclotron Range of Frequency Heating / Special Issue on Large Helical Device (LHD) /

Various ion cyclotron range of frequencies (ICRF) heating experiments have been conducted in the Large Helical Device (LHD) by changing the magnetic field strength and the wave frequency using hydrogen and helium. When the resonance layer of hydrogen was located in the peripheral region on the lower-magnetic field side, efficient electron heating, i.e., mode conversion heating, was realized. When the ion cyclotron resonance layer was located near the "saddle point" of magnetic field strength, where the gradient of the magnetic field strength is zero, hydrogen ions were efficiently heated by the minority ion heating. The second-harmonic ion cyclotron heating experiments were also conducted by decreasing the magnetic field strength, and the plasma was successfully sustained for 1 s. Ion tails were observed in the ion heating modes. High-energy ions were well confined by the inward-shifted magnetic configuration. The ion tail formed by the second-harmonic heating was enhanced by the injection of a perpendicular neutral beam.

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