In the recent past, the emphasis in solar wind research has been on its composition (Ulysses and ACE) and on phenomena at large heliocentric distances (Ulysses, Voyager). At 1AU, Plasma-Mag will contribute new information at low solar latitudes about Coronal-Mass Ejections (CMEs), magnetic clouds, and the electron "super halo". This will be an improved follow-on investigation to the data provided from WIND. Plasma- Mag studies will be focused on two major problems: 1) the source and structure of the slow solar wind, and 2) mechanisms for heating the solar corona.
The mechanisms for heating the solar corona to temperatures that are much hotter than the photosphere are not well understood. Waves in the solar wind appear to undergo a turbulent cascade to heat the wind at small scales. Reconnection events also lead to heating and acceleration of particles. More generally, the coupling between magnetic and electric fluctuations and particle distribution functions is a fundamental plasma interaction, important in a variety of contexts. The mechanisms are not well understood, and are difficult to study directly.
The improved time resolution of Triana/Plasma-Mag provides an opportunity to determine the mechanism by which small-scale fluctuations dissipate in plasmas. A time resolution of less than 1 second would provide information to determine how the plasma responds to the simultaneously measured magnetic fields. It would also provide critical observational input to test and further develop theories of wave damping and the heating and acceleration of particles expected to take place near the proton cyclotron frequency. Moments of the distribution functions, at the highest resolution, would make it possible to determine if the waves are Alfvenic (or on a higher frequency extension of this wave mode), and if so, to discern their direction of propagation. Detailed distribution functions would also enable us to test kinetic theories of the interaction, since the time resolution enables measurement at spatial scales comparable to the proton gyroradius.