A MODIFIED THERMAL-CONDUCTIVITY FOR LOW-DENSITY PLASMA MAGNETIC-FLUX TUBES

In response to inconsistencies which have arisen in results from a hyd rodynamic model in simulations of high ion temperatures (1-2 eV) obser ved in low density, outer plasmasphere flux tubes, we postulate a redu ced thermal conductivity co-efficient in which only particles in the l oss cone of the quasi-collisionless plasma contribute to the thermal c onduction. Other particles are assumed to magnetically mirror before t hey reach the topside ionosphere and therefore not to remove thermal e nergy from the plasmasphere. This concept is used to formulate a mathe matically, simple, but physically limiting model for a modified therma l conductivity coefficient. When this modified coefficient is employed in the hydrodynamic model in a case study, the inconsistencies betwee n simulation results and observations are largely resolved. The high s imulated ion temperatures are achieved with significantly less heat in put, and result in substantially lower ion temperatures in the topside ionosphere. We suggest that this mechanism may be operative under the limited low density, refilling conditions in which high ion temperatu res are observed.