Alfvénic acceleration of solar wind helium and related phenomena 1. Theory
Abstract
We present a new physical mechanism by which helium nuclei can be preferentially accelerated by Alfvén waves in the solar wind. The mechanism works as follows. The acceleration of the solar wind by Alfvén wave pressure is basically a δJ × δB force; but the wave-associated current δJ carried by a given plasma species depends, via the Lorentz transformation, on the bulk velocity of that species, and thus species that move at different bulk velocities experience different accelerations. In the solar wind this differential acceleration can for the most part be interpreted as an additional frictional interaction between protons and helium nuclei. Numerical estimates indicate that this interaction is important at 1 AU. It is expected that this additional friction will be able to account for the observed fact that helium nuclei almost never flow slower than protons in the solar wind; detailed numerical calculations are deferred to a later paper, however. Although our calculation is done for Alfvén waves, we argue that the basic physics of our mechanism is applicable to a wide variety of waves, and we suggest that it may be important for cosmic rays, interstellar gas, comet tails, and the earth's (and Jupiter’) geomagnetic tail.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- 1974
- DOI:
- 10.1029/JA079i010p01357
- Bibcode:
- 1974JGR....79.1357H
- Keywords:
-
- Particles and Fields-Interplanetary Space: Solar wind magnetic fields;
- Particles and Fields-Interplanetary Space: Solar wind plasma