Abstract
H-modes produced by ion-cyclotron resonance heating (ICRH) in a double-null X-point open divertor configuration in the JET Tokamak are studied, where the ICRH antennas, operated in the dipole (0, pi ) phasing, are located on the low-field side of the Tokamak. Beryllium evaporation on the nickel antenna screen and the first wall of the Tokamak played a crucial role in achieving H-modes with ICRH alone. In these discharges, all the characteristics typical of neutral-beam injection heating H-modes are found, and the global energy confinement time approaches two times the Goldston L-mode prediction. For most of their duration, ICRH H-modes are free from ELMs (edge-localized modes). In addition, the monster sawtooth (long sawtooth-free period) feature of ICRH is maintained during H-modes, leading to a central electron temperature (Tc0) of 10 keV, nearly twice the value of the central ion temperature (Ti0). ICRH H-modes often occur as a two-step transition and the antenna plasma coupling resistance (Rc) also decreases in two steps. Theoretical values of Rc agree well with experimental values during the H-phase.
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