SAIP2012

Ion-Bernstein waves in a plasma with a kappa velocity distribution

10 Jul 2012, 17:30

2h

IT Building

Poster Presentation Track D2 - Space Science Poster Session

Speaker

Mr Francois Nsengiyumva (University of KwaZulu-Natal)

Level for award<br>&nbsp;(Hons, MSc, <br> &nbsp; PhD)?

PhD

Apply to be<br> consider for a student <br> &nbsp; award (Yes / No)?

yes

Abstract content <br> &nbsp; (Max 300 words)

Bernstein waves have been observed in many planetary magnetospheres. Particle observations indicate that space plasmas often have charged particles with a strongly non-Maxwellian tail on their velocity distributions. In particular, they often exhibit power law dependence on velocity in the higher energy range. Such velocity distributions may be modelled by the kappa
(generalized Lorentzian) distribution with low values of kappa.

We have carried out a study of low frequency ion-Bernstein waves in space plasmas, using a Vlasov-Poisson model based on the kappa velocity distribution. The general dispersion relation obtained by Mace [1] for a multi-species kappa plasma is specialised to the case of singly charged ions and electrons. This dispersion relation is solved numerically, without approximations, for the ion-Bernstein mode. It is shown that for low values of the ion-kappa index, the dispersion curves differ significantly from those predicted by Maxwellian theory.

Ion-Bernstein waves propagating in the band below the lower-hybrid frequency have frequencies given by nωci at vanishing wave number k⊥ and fall to (n − 1)ωci as k⊥ is increased. It is found that the rate at which this frequency decrease occurs depends strongly on the kappa index of the ions, with lower values of kappa exhibiting a less rapid fall-off.

Above the lower-hybrid frequency, ion-Bernstein waves have a different dependence on wave number. While at vanishing k⊥ the frequency approaches nωci, it then increases with k⊥ to a peak at a value k⊥peak before the frequency drops to nωci for large k⊥. It is shown that both the wave number k⊥peak and the peak frequency depend on the ion-kappa value.

In the lower-hybrid frequency band, the ion-Bernstein waves exhibit features intermediate between those described above. The dispersion relation of the mode in this band is also affected by the ion-kappa index.

References

[1] R. L. Mace, Phys. Plasmas, 10, 2181 (2003).

Main supervisor (name and email)<br>and his / her institution

Prof. Manfred Hellberg, Email: hellberg@ukzn.ac.za, Institution: University of KwaZulu-Natal.

Would you like to <br> submit a short paper <br> for the Conference <br> Proceedings (Yes / No)?

No