Spontaneous emission of a charged particle beam inside a plasma - Coherent and incoherent aspects

A continuous emission with a one-to-one relation between wave amplitude and nominal beam current, and a pulsed emission which reaches a maximum amplitude a few msec after the begining of an electron pulse and then continuously decreases to a background value, are noted in experiments involving the injection of a charged particle beam into an ionospheric plasma. Spontaneous emission, and especially Cerenkov emission, is a good candidate for an explanation of these observations. An attempt is made in the present discussion to give numerical estimations of the effects in question in order to compare them with observed values. Attention is given to the possibility of an increase in coherent emission with the use of a charged beam as a VLF antenna.