Beam instabilities in a magnetized pair plasma

Beam instabilities in the strongly magnetized electron-positron plasma of a pulsar magnetosphere are considered. We analyse the resonance conditions a nd estimate the growth rates of the Cherenkov and cyclotron instabilities o f the ordinary (O), extraordinary (X) and Alfven modes in two limiting regi mes: kinetic and hydrodynamic. The importance of the different instabilitie s as a source of coherent pulsar radiation generation is then estimated, ta king into account the angular dependence of the growth rates and the limita tions on the length of the coherent wave-particle interaction imposed by th e curvature of the magnetic field lines. We conclude that in the pulsar mag netosphere, Cherenkov-type instabilities occur in the hydrodynamic regime, while cyclotron-type instabilities occur in the kinetic regime. We argue th at electromagnetic cyclotron-type instabilities on the X, O and probably Al fven waves are more likely to develop in the pulsar magnetosphere.