Instability of lower-hybrid waves in collisional plasmas with a field-aligned current

A study is presented for electrostatic waves propagating at large angles with respect to the background magnetic field in collisional, fully ionized plasmas carrying a field-aligned current. In addition to a mode at the usual lower-hybrid frequency, it is found that the presence of electron drift velocity introduces two more modes of oscillation at several times the lower-hybrid frequency. Under appropriate conditions, a resistive instabifity, with frequency very close to the lower-hybrid frequency and growth rate proportional to the electron-ion collisional frequency, can occur. A necessary condition is that the parallel phase velocity of the wave be smaller than the electron drift velocity. A numerical example is given to illustrate the essential features of the instability.