Abstract
Density fluctuations in the ion-cyclotron frequency range have been observed in the TFR tokamak by microwave scattering. The geometry was such that the selected fluctuation wave vector was aligned across the confining magnetic field in the outside region of the torus. A threshold for the onset of the instability as a function of the discharge current has been observed. A plausible explanation of this instability in terms of current-driven ion-cyclotron electrostatic wave is discussed.