The beam pulse amplifier in space and laboratory plasmas

We discuss the physical background of the a new mechanism in which short electromagnetic pulses can be strongly amplified by interaction with suprathermal electrons in a near-equilibrium near-uniform magnetised plasma layer. This occurs under the special condition that the wave phase and group speeds along the field lines are equal, a condition met by extraordinary mode electromagnetic waves propagating in the medium. In this case the pulse interacts strongly via the Čerenkov resonance with suprathermal electrons moving along the field lines at the same speed as the pulse, leading to rapid wave growth, the instability within the pulse being shown to be equivalent to that of a monoenergetic electron beam moving along the field lines in an infinite uniform plasma. This effect accounts for basic features of powerful pulsed electromagnetic emissions in planetary magnetospheres, specifically whistler-mode chorus emissions in space plasmas, the remarkable radio emissions observed from brown dwarf objects, as well as in laboratory plasma.