Invited paper: Anomalous k-spectrum in current driven ion-acoustic instabilities

Often cross-correlation measurements on current driven ion acoustic instabilities in a strong magnetic field indicate so-called anomalous k-spectrum which severely deviates from what is expected from the angular dependence of the linear growth rate. Several mechanisms have been proposed recently, including nonlinear Landau damping on ions and quasilinear deformation of electron distribution function governed by binary collisions. It is shown that quasilinear evolution of high energy ion tail has a strong influence on the spectrum. Preferential ion tail formation along the electron drift makes the growth rate profile (initially almost isotropic hemispherically about the electron drift) strongly anisotropic