Electrostatic wave generation by the Faraday shield in ICRF heating

The generation of fringing fields by the Faraday shield of a fast wave antenna and the concomitant coupling of the wave power to electrostatic waves is analysed for the case of weakly misaligned screen blades. The coupled electrostatic wave power is found to be proportional to sin2β, where β ≤ 1 is the misalignment angle. Under optimum conditions when the angular frequency is just below the first harmonic of the cyclotron frequency of any ion species and the plasma density near the shield is high, 10-20% of the loading of the antenna may result from ion Bernstein wave excitation with β=0.1. (orig.)