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H-modes, produced by ion-cyclotron resonance heating (ICRH) in a double-null X-point open-divertor configuration in the JET tokamak, were studied. The ICRH antennae, operated in the dipole (0, pi) phasing were located on the low-field side of the tokamak. The 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. These H-modes have a duration of up to 1.5 s with an ICRH power level of up to 12 MW. In these discharges, all characteristics typical of neutral-beam injection heating H-modes are found, and the global energy confinement time approaches twice the Goldston L-mode prediction. For most of their duration, ICRH H-modes are free from ELMs (Edge Localised Modes). In addition, the monster sawtooth (long sawtooth free period) feature of ICRH is maintained during H-modes leading to a central electron temperature T(e0) of 10 keV, nearly twice the value of the central ion temperature T(i0). In NBI heating H-modes, the T(e0) is generally lower than the T(i0) but the combined ICRH + NBI heating H-modes allow both T(e0) and T(i0) close to 10 keV simultaneously. The elevated T(e0) by ICRH in the combined heating increases the slowing down time of beam ions and increases the D-D reaction rate and the neutron output. ICRH H-modes often occur as a two-step transition and the antenna plasma coupling resistance (R(c)) also decreases in two steps. Theoretical values of R(c) agree well with experimental values during the H-phase.

Additional information

Authors: BHATNAGAR V P, JET Joint Undertaking, Abingdon, Oxon. (GB);JACQUINOT J ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB);HATAYAMA A, Toshiba Corporation Chome, Chiyoda-Ku, Tokyo (JP);LAWSON K, UKAEA, Culham Laboratory, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(90)44 EN (1990) 33 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199110038 / Last updated on: 1994-12-02
Original language: en
Available languages: en