Role of ion Bernstein waves in ICRF experiments

The influence of the ion Bernstein wave, both parasitic and direct, on wave excitation in the ion cyclotron frequency range is presented. Excitation of ion Bernstein waves from electromagnetic loop antennas polarized to produce either B₀ or B_z is sstudied both in theory and experiment. Local analysis is applied to the Maxwell equations to include the effect of a density gradient which has a scale length comparable to the wavelength. The antenna is composed from a Fourier sum in the directions transverse to the gradient. Results of experiments on the ACT‐I research torus are presented for comparison with theory. Both linear and parametric excitation are observed. In each case the excitation process is studied over a range of plasma density, and wave frequency and parallel wavenumber.