Investigations of electrostatic ion waves in a collisionless plasma

This report reviews a series of publications concerning theoretical and experimental investigations of electrostatic ion waves in a collionsless plasma. The experimental work was performed in the Risø Q-machine under various operational conditions. Besides a description of this machine and the diagnostic techniques used for the measurements, two kinds of electrostatic waves are treated, namely, ion-acoustic waves and ioncyclotron waves. Due to the relative simplicity of the ionacoustic waves, these were treated in detail in order to get a more general understanding of the behaviour of the propagation properties of electrostatic waves. The problem concerning the difficulties in describing waves excited at a certain position and propagating in space by a proper mathematical model was especially considered in depth. Furthermore, ion-acoustic waves were investigated which propagated in a plasma with a density gradient, and afterwards in a plasma with an ion beam. Finally, a study of the electrostatic ion-cyclotron waves was undertaken, and it was shown that these waves were unstable in a plasma traversed by an ion beam.