ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
An analytic and numerical study is made of the effects caused by coherent density fluctuations, localized near the ion–ion hybrid resonance, on the propagation and absorption of fast Alfvén waves. The system is represented by a Budden equation that incorporates static fluctuations in the ion density profiles. The unperturbed system contains a resonance at x=0 and a cutoff at x=d; the Alfvén wave number at resonance is kA. Two cases are considered: fluctuations in the ion concentration ratio η and bulk density fluctuations. When the incident wave directly approaches the resonance, the fluctuation in the concentration ratio δη/η0 is less than 20%, and kAd〈1, a "renormalized'' Budden potential yields analytic expressions in good agreement with numerical results. In this regime, the reflection coefficient exhibits a new contribution arising from the modifications of the resonance layer. For direct approach, kAd〉1, and concentration fluctuations 2%〈δη/η0〈5%, enhanced reflection leads to decreased absorption. For these parameters, the net absorption is reduced by more than 10% for noise wave numbers larger than 10 kA. However, the efficiency of the resonant absorption process remains unaffected. For kAd〉2 and fluctuations δη/η0〉5%, a regime of multiple resonances is encountered in which substantial absorption results. For indirect approach, a similar process takes place: The reflection coefficient is reduced from its unperturbed ∼1 value to ∼0. For bulk fluctuations, backscattering is the dominant physical process.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.859422
Permalink
