The paper considers the coupling efficiency of a multi-current antenna inserted into a special conducting recess and designed to excite magneto-acoustic waves in the ion-cyclotron (IC) frequency range to heat the dense hot plasma in large tokamaks. To find the antenna impedance, the k||-spectra of the exciting field and the power flux, the fields in the two regions of the recess presented as a superposition of eigenmodes, are matched to each other at the level of the exciting current and are then matched to the field in the plasma calculated by the Airy function method. Taking the recess into account gives rise to a severe weakening of the plasma coupling and a change in the excited wave spectrum. The theory developed here can be used to calculate the antenna for ICR heating of plasmas in the new-generation tokamaks now under construction (T-15, TFTR, JET, JT-60) and tokamak reactors at the design status (INTOR, FED, etc.). As an example, the paper analyses the characteristics of an antenna constructed on current conductors and designed to supply 12.5 MW of high-frequency power at 85 MHz to an INTOR plasma.
First experimental results with new ICRF antenna in EAST