Further Study of Ion Pickup. Turbulent Alfven waves and magnetic field lines Turbulent waves represent enhanced random fluctuations. Fluctuations vitiate.

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.