Quasilinear Theory of the Ion Cyclotron Instability and Its Application to the Cometary Plasma
- Alan Johnstone
Published Online: 26 MAR 2013
Copyright 1991 by the American Geophysical Union.
Cometary Plasma Processes
How to Cite
Galeev, A. A., Sagdeev, R. Z., Shapiro, V. D., Shevchenko, V. I. and Szego, K. (1991) Quasilinear Theory of the Ion Cyclotron Instability and Its Application to the Cometary Plasma, in Cometary Plasma Processes (ed A. Johnstone), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM061p0223
- Published Online: 26 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900278
Online ISBN: 9781118663660
- Space plasmas;
The quasilinear theory of Alfven turbulence in the mass-loaded solar wind is reviewed and compared with observations obtained in the upstream region of comet Halley's bow shock. The theory explains the formation of the shell distribution of the cometary ions from the initial ring distribution as the result of the pitch angle diffusion caused by Alfven waves. In situ measurements of wave intensity, frequency spectrum and polarisation of Alfven waves also agree well with the predictions of the ion cyclotron instability, driven by cometary ions. The turbulence in the vicinity of the comet Giacobini-Zinner seems to be somewhat different—while being more intense it is essentially more regular in its nature. The main reason for this difference is due to the fact that in the latter case, with smaller gas production rates, turbulence develops significantly closer to the comet.
The possibility of the excitation of oblique magnetosonic waves accompanied by density fluctuations is analysed. The mechanism for such excitation is wave refraction on the transverse inhomogeneities in the solar wind. It is shown that in the vicinity of the bow shock the intensity of magnetosonic waves grows rapidly.
The acceleration of the cometary ions in the mass-loaded solar wind by MHD turbulence (stochastic Fermi acceleration) is also analysed in the paper. It is shown that the softest part of the spectrum of the accelerated ions could be attributed to the acceleration by oblique magnetosonic waves while the main acceleration is due to the long wavelength firehose magnetic field perturbations. The ion energy spectra obtained by solving the energy diffusion equation are compared with observations.