New advances in thermal plasma research

Recent measurements obtained of the cold or thermal plasma of the earth's magnetosphere, which is believed to originate in the ionosphere, are reviewed. Consideration is given to the results of ATS 6 measurements which indicated unexpectedly high plasma temperatures and varied pitch-angle distributions, and the data from the low-energy plasma experiments on board GEOS 1 and 2 and ISEE 1, which were intended to clarify the ATS 6 results. These later measurements of ion composition, plasma energy and plasma distribution are noted to have confirmed earlier data and discovered new plasma components (D(+) or He(+2)), an intermixing of cold ionospheric plasma and hot magnetospheric plasma, the ordering of the plasma by the magnetic field rather than the ram direction in the outer magnetosphere, and wave phenomena. Questions remaining concerning the temperature and composition distributions of the plasmasphere and plasma trough, the relative densities of the cold and warmer components of the magnetosphere, plasma energization mechanisms, and the relative mix of the various plasma distributions are indicated.