Further Study of Ion Pickup

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.

Simulation results show that pickup is very rapid in general.