comparison of our computed Joule heating rate with the normal sunlit EUV absorption rate of the sunlit thermosphere. The strength of the electric field [[spi:math]] is assumed to be 10 mV/m for easy scaling to other values. It is seen that the beam induced electric field is a significant heat source of the thermosphere at the foot of the flux shell on which the SPS ion engine beam is located. The net effect of this prompt thermospheric heat source must be folded into the later heating effects due to precipitation of the beam ions. The actual heating scenario cannot be estimated unless very complicated timedependent thermospheric models are used. However, observations of trans- plasmaspheric flow (Vickrey et al., 1979) between the sunlit and nightside ends of flux tubes indicate that ionospheric heating is likely to be spread to other regions of the plasmasphere within a diurnal cycle. Thus, evaluation of transient heating effects at a later stage of the assessment would be very enlightening. Present work pertaining to this area include Schlegel and St. Maurice (1980) and Wickwar et al. (1980). D. Plasmaspheric Heating The temperature of the plasmasphere is usually well below ~ 104°K except in the regions of the plasmapause where heating by wave turbulence causes the temperature to rise to ~ 104°K and above. In the auroral region, energetic particle temperatures can range to tens of keV. With physical processes similar to auroral processes occurring in a flux tube connecting the argon ion beam and the ionosphere, we would expect plasmaspheric heating not unlike that occurring in the auroral flux tubes. Heating, being the final stage of energy transformation from the 3.5 keV free energy of the COTV beam, is particularly difficult to model for the plasmasphere where the density is too low for fluid models and too high for kinetic models. Noting that Joule dissipation of the COTV beam energy is similar to auroral Joule dissipation and noting that local 43
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