This picture of argon beam plasma cloud interaction with the magnetosphere is based on high [[spi:math]] explosive barium releases in the far magnetosphere (Pilipp, 1971; Scholer, 1970). The 0 of ion engine exhaust is much greater, but a second indication of the action of an Alfven shock to short out the polarization electric field can be found in the stopping of Starfish debris motion perpendicular to the magnetic field (Zinn et al., 1966), although for this case [[spi:math]] is again not as large as the case of the argon ion beam. The basic physics invoked here have also been applied to the resolution of the observed anomalous magnetic drag on satellites of the ECHO series (Drell et al., 1965); and more recently, applications to the Jupiter-Io momentum transfer problem have also been made (Southwood et al., 1980). This mechanism allows the major part of the beam momentum to be soaked up by the magnetospheric and ionospheric plasma, resulting not necessarily in a uniformly cold argon plasma, but in one with some hot argon plasma components trapped in the magnetic field due to pitch angle scattering. These hot components act much like an argon ring current. Numerical models of this process for realistic plasmaspheres have been constructed in FY80 and our results have essentially borne out these expectations. The essential point to be recognized is that the momentum transfer process takes place via the Alfven speed (~ 10 times the beam speed). It is sometimes claimed that the beam regime is trans-Alfvenic , i.e., vA <= v, and that the physics of beam stopping is different because the beam speed is too fast for the Alfven shock to act. However, actual calculation of plasmaspheric Alfven speeds, as in Figure 9, based on a plasmasphere model which compares favorably with observations (Chiu et al., 1979b), shows conclusively that the 3.5 keV argon ion beam is everywhere sub-Alfvenic. 19
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