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Priming the Electron Distribution

A heating or "priming" of the electron distribution beyond the heliopause is an important component of our group's theory for the outer heliospheric radio emission. The process begins when high speed neutral particles, formed by collisions between solar wind protons and interstellar medium neutrals in the inner heliosheath, cross the heliopause and enter the outer heliosheath and interstellar medium. These high speed particles collide with interstellar protons and undergo charge exchange for a second time giving rise to high speed protons which are then "picked up" by the local magnetic field and begin to gyrate about it (hence they are called "pick-up ions"). The pick-up ions form a ring-beam distribution in velocity space with the ring perpendicular to the magnetic field, which can generate lower-hybrid waves. These waves in turn can resonantly accelerate electrons, forming a non-thermal tail on the electron distribution. This process is known as lower-hybrid drive (LHD).

Recent work in this area predicts that the inclusion of the LHD tail may increase the power of shock driven radiation by four orders of magnitude. As well as conducting research into the implications of electron distibution priming, our group is also working to improve the current model of the LHD process.

Publications

1. I.H. Cairns and G.P. Zank, Turn on of the 2-3 kHz radio emission Beyond the heliopause, Geophys. Res. Lett., 29(7), 47, 2002.
   
2. J.J. Mitchell, I.H. Cairns and P.A. Robinson, Theory for the 2-3 kHz radiation from the outer heliosphere, J. Geophys. Res., 109, A06180, 2004.
   
3. J.J. Mitchell, I.H. Cairns, H.-R. Müller, G.P. Zank, Timing of the 2-3 kHz radio emission within the solar cycle, Geophys. Res. Lett., in press, 2005.

Other outer heliosphere projects

1. The propagation of radiation using ray tracing
2. Draping of the magnetic field over the heliopause
3. Radio emission in the outer heliosphere

Figure 1. The proton distribution showing velocity perpendicular to B. The peak in the middle contains the background thermal protons and around the edges are the pick-up ions in a ring-beam.

Figure 2. The electron speed distribution showing the thermal background (full line) and the non-thermal LHD tail (dashed line).