Fast wave antenna coupling to slow waves and ion Bernstein waves during ICRF heating of tokamak plasmas
The coupling of the fast wave antenna to short wavelength waves, due to an imperfect alignment of the antenna screens along the magnetic field lines of a tokamak plasma, is analysed. Analytical and numerical estimates for the fraction of the power going into the short wavelength modes are given for various edge plasma parameters and their profiles. The functional dependence of this fraction on the screen angle and on the excited spectrum of the short wavelength waves is computed. According to the results a non-negligible amount of power could be radiated from the present ICRF antennae in the form of ion Bernstein waves or slow waves for realistic edge density profiles. For edge plasmas extending to the screen, the excited electrostatic wave spectrum is peaked for large parallel refractive indices n(z) and the total radiation resistance reduces as the angle between the screen blades and the magnetic field lines increases. The opposite is found to be true when the density near the screens is sufficiently low to allow the presence of the slow mode resonance. Possible connections between these phenomena and the deleterious edge modification and enhanced impurity influx from the antennae observed in the heating experiments of JET are discussed.
Bibliographic Reference: Report: JET-P(89)40 EN (1989)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199010669 / Last updated on: 1994-12-01
Original language: en
Available languages: en