## Abstract

The effects of lithium and heavier ions (i.e. having specific charge Z_{j}e/m_{j}smaller than the proton's), on the electromagnetic cyclotron instability in warm anisotropic (bi-maxwellian) proton plasmas, are analytically and numerically investigated. It is found that the occurrence of resonances for modes with ω_{r}= Ω_{j}. (ω_{r}, real wave frequency; Ω._{j} ion gyrofrequency), which produce a cut-off in the phase velocity, leads to the possible existence of two different situations, (i) If the proton thermal anisotropy A_{p} = (T⊥/T_{||})_{p}—1 is smaller than a critical value A^{c} _{p}(which depends on the ion specific charge), the resonance and therefore the 'stop band' occurs outside the unstable range. The maximum growth rate, as well as the instability range in k space, may increase with the relative ion concentration η_{j}≡Z_{j}n_{j}/n_{p, w} (n_{jnp,w}: ion and warm proton particle densities, respectively). There is an optimum value of η for maximum enhancement of the instability, (ii) If A_{p} > A^{c} _{p} the unstable spectrum in ω_{r} space is divided by the 'stop band' into two distinct regions. In the higher-frequency region, the maximum growth rate, as well as the width of the unstable spectrum, decrease with increasing relative ion concentration. For η> η^{c} the instability is completely suppressed. In the lower-frequency region, however, the maximum growth rate and the extension in k space may increase with η.

Original language | English |
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Pages (from-to) | 195-207 |

Number of pages | 13 |

Journal | Journal of Plasma Physics |

Volume | 14 |

Issue number | 2 |

DOIs | |

State | Published - Oct 1975 |