There are observations of broadband electrostatic noise in the plasma sheet boundary layer that are associated with field-aligned current (electron beams), which often have an upper cutoff frequency above the electron plasma frequency. In this paper, using linear theory and numerical simulations we present results from a study of instabilities caused by an electron-beam in a thermally mixed plasma. It is shown that two instabilities, the electron acoustic and electron ion instabilities can combine to form a broadbanded wave spectrum that rapidly destroys the electrom beam. ¿ American Geophysical Union 1989