Processes in the Magnetotail Neutral Sheet

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This paper reviews neutral sheet observations and theories emphasizing particle acceleration or "inertial dissipation". The existence of the central current sheet and cross-tail electric field in the magnetotail neutral sheet implies an energy dissipation which is roughly a few percent of the incident solar wind power on the entire magnetosphere. This is an important - if not the dominant - energy dissipation in the magnetosphere. Earthward streaming ions in the plasma sheet boundary layer can result from simple single particle acceleration in the current sheet and these beams carry sufficient energy to account for this dissipation. Although stochastic processes need not be invoked, "inertial conductivity" is inferred from the time the particles spend undergoing acceleration within the current sheet. The particle motion thus leads to simple consistency "equilibrium states" and the motion has been used as the basis of an explosive reconnection model by Coroniti. Finally, observations and theories of broadband electrostatic noise, which may also provide dissipation, are reviewed. Particle distributions which result from neutral sheet energization will likely be unstable to the growth of plasma waves. Broadband electrostatic noise is the most intense and frequently occurring plasma wave mode in the magnetotail and the intensity is observed to peak in the plasma sheet boundary layer. It is thought to be excited by the ion beam acoustic instability. Resonant heating of plasma sheet boundary layer ions may be responsible for the hot ion component of the central plasma sheet.