Finite β drift Alfvén instability

We propose a means by which the theory of drift instabilities can be extended to plasmas of arbitrary β. We then concentrate on the drift Alfvén instability driven by an electron temperature gradient, proposed by Coroniti and Kennel (1970) to be a source of Pi 1 micropulsations on auroral lines of force. Even at relatively low β the full finite β theory differs considerably from previous low β theories and produces better agreement with observation.