Excitation, propagation, and absorption of directly launched ion Bernstein waves were studied with ${\mathrm{CO}}_2$ laser scattering in the Alcator C tokamak. Optimum excitation is obtained when an ion-cyclotron harmonic layer is located just behind the antenna. Wave absorption at the ω=3${\Omega }_{\mathrm{D}=1.5\mathrm{}{\Omega }_{\mathrm{H}}}$ layer was observed. 3 It may be necessary to control the edge density fluctuation level in order to minimize scattering of the ion Bernstein waves and optimize heating.

• Received 24 November 1986

DOI:https://doi.org/10.1103/PhysRevLett.59.1201