further study of ion pickup. turbulent alfven waves and magnetic field lines turbulent waves...
Post on 19-Dec-2015
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Turbulent Alfven waves and magnetic field lines
• Turbulent waves represent enhanced random fluctuations.
• Fluctuations vitiate the basic concept of smooth magnetic field lines which are defined in macroscopic sense.
Stochasticity in Space and Time
• Turbulence makes the local magnetic field at a given time or spatial location random and unpredictable.
• Therefore there is no advantage to use the concept of “magnetic field lines”.
Up to early 1990s our understanding of ion pickup
was:
• Ions moving with velocities different from the Alfven speed may be trapped by the waves, and be picked up.
• Interaction between ions and waves is via cyclotron resoance.
• If the level of turbulence is sufficiently high, a spherical shell velocity distribution may be formed.
Review of the pickup issue
• The relative velocity between the wave frame and the particles of interest is an essential parameter.
• In the solar wind the newborn ions are very fast and therefore their energy gain is substantial.
• Can we find some other cases in which this acceleration process is significant?
Cometary Observations
• ICE passing by comet Giacobini-Zinner in 1985.
• Satellite observations stimulated great interest in the study of pickup process
• Much progress was made in mid to late 1980s
Possible applications to micro-flares
• Observations seem to see that micro-flares occur everywhere in the solar atmosphere.
• Magnetic reconnection process play key roles.
Acceleration in a reconnection layer
by pickup process
• If reconncetion occurs in a region where the local Alfven speed is high, it is known that outflow is fast.
• If newborn ions are produced near the reconnection point, these ions can be accelerated by pickup process.
A Numerical Simulation Study
• Use MHD simulation result to do test particle simulation.
• Assume that ionization process takes place.
• Study ion acceleration due to pickup process.