Lower hybrid heating of ionospheric ions due to ion ring distributions in the cusp

Abstract

The stability of H+ and He++ ring distributions which have been observed downflowing into the cusp on the DE and S3‐3 satellites is examined in the context of the feedback of those instabilities on plasma of ionospheric origin (H+ and O+). Lower hybrid waves are excited by the ring distributions in three distinct phases of wave‐particle interaction: linear growth, trapping, and quasi‐linear diffusion. The latter phase accounts for most particle heating. Including background O+ and/or a He++ ring introduces new modes not present in a pure H+ plasma which play an important role in heating heavier ions. O+ is heated significantly more by a He++ ring than a H+ ring of comparable energy density. It is suggested that lower hybrid waves generated by downflowing ion ring distributions play a role in energizing ion conies in the cusp.