Electromagnetic ion-cyclotron instability vs. electrostatic ion-cyclotron instability in mixed (warm-cold) magnetospheric-like plasmas

S. Cuperman, L. Gomberoff

Research output: Contribution to journalArticlepeer-review

Abstract

This work presents a systematic investigation and comparison of electromagnetic ion-cyclotron (e.m.) and electrostatic ion-cyclotron (e.s.) instabilities in uniform mixed warm and cold plasmas for magnetospheric-like plasma parameters. The following main aspects are included: Analytical: (i) we derive simple approximate expressions for the maximum growth rate, ymax for the quasi-electrostatic instability in the regime (or >Qp k± >„ („ =t= 0) with the protons being described by mixed loss-cone and cold populations and with inclusion of electromagnetic coupling effects due to electrons; (ii) we analyse another regime in which electrostatic instabilities first increase with addition of cold plasma and decrease only after having reached a maximum, namely a regime with «, >Q,, k = k±; (iii) we summarize the corresponding analytical results for parallel propagating electromagnetic ion-cyclotron unstable waves and discuss their validity range. Numerical: we solve numerically the exact linearized dispersion equations for the cases mentioned above, for a number of physical situations of magnetospheric interest. Comparison and discussion: The analytical and the numerical results are compared for each type of instability and next for various instabilities. Special attention is paid to the convective vs. non-convective character of each type of wave; this is done by investigating the maximum values of the convective growth rates, Smax = (Yklvg,k, n)max, Jk being the growth rate and vOtkJI the parallel group velocity of the mode k. At relatively low cold plasma concentrations (i.e. njnw < 1), y £ >7. f°r a u values of the parameter fip>, = 8nnw x KTJB% smaller or of the order of one. However, Sx < S%j£s.>n a t is ° * n instabilities are effective. The relative importance of the e.m. mode (expressed in terms of Smax) increases with njnw and soon becomes dominant. The larger fiPi, is, the faster this situation arises. Unlike y i. lk increases with njnw until njnw reaches a specific value, decreasing thereafter.

Original languageEnglish
Pages (from-to)391-413
Number of pages23
JournalJournal of Plasma Physics
Volume18
Issue number3
DOIs
StatePublished - Dec 1977

Funding

FundersFunder number
United States-Israel Binational Science Foundation

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