Space Sciences Laboratory, University of California, Berkeley
In the near Earth plasma sheet, the three dimensional plasma and energetic particle investigation (3DP) on the Wind spacecraft has detected very rapid (< 1 second) changes in the electron distributions. The changes generally consist of a transition from a relatively high density, low temperature distribution to a low density, higher temperature distribution. These changes coincide with intervals of large magnetic field fluctuations, large ion velocity moments, and increases in the flux of energetic particles. The goal of this work is to determine whether the electrons are accelerated in situ or if two distinct electron populations are being sampled as the boundary between them is swept by the spacecraft. First results indicate that the change in the electron distributions is nonadiabatic in both the thermodynamic sense, i.e., the specific entropy is not constant, and in the kinetic sense: the first adiabatic invariant is not conserved. Since changes in the magnetic field coccur on timescales much longer than the electron gyroperiod, one would expect that for a local acceleration process the first adiabatic invariant would be conserved in the absence of invariant breaking processes such as wave-particle interactions. Although we cannot rule out nonadiabatic in situ acceleration, the simplest interpretation is that the electrons are accelerated elsewhere and transported to the observation point with the boundary between the ambient and accelerated electrons passing over the spacecraft in less than one second.
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