Coherent nonlinear interactions in phase space resolved ion density fluctuations
Başlık çevirisi mevcut değil.
- Tez No: 400456
- Danışmanlar: PROF. Frederick Skiff
- Tez Türü: Doktora
- Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2006
- Dil: İngilizce
- Üniversite: Unıversıty Of Iowa
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Fizik Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
Using Laser Induced Fluorescence(LIF) diagnostics and higher order spectral analysis, we present the first measurements of phase space resolved quasi-coherent nonlinear interactions among the components of the low frequency density fluctuation spectrum(! ? !ci) in a linearly magnetized device. Higher order spectral analysis, especially bicoherence results suggest that there are two different coherent nonlinear wave-wave interactions in the measured density spectrum. The one, having a short decay length and existing for slow moving ions, for which i|| ? th,i, is an interaction between the drift wave frequency, !?, and its sub-harmonics. The second one is existing for fast moving ions, for which i|| ? th,i, and is a nonlinear wave-wave interaction between the drift wave frequency and its second harmonic. Preliminary analysis of the data based on the cross-power spectral density calculations showed us that the fluctuation spectrum has a distinctive, broad peak near the drift wave frequency(!?) that can be dissected into two components; the one having a long wavelength consistent with drift wave theory, and the other, which we call the `kinetic component?, with a shorter correlation length and ion particle velocity dependence. Combining both results, we suggest that the observed nonlinear interactions between the drift wave and its sub-harmonics are clearly effected by the kinetic coherent structure. When the ion-neutral and electron-neutral collision frequencies are increased by increasing the neutral pressure, the kinetic component vanishes and spectral condensation occurs in the cross power spectrum. On the other hand, the simulation results show us that 2 the drift wave becomes more unstable for increased neutral pressure and suppression of higher order radial modes is predicted. The bicoherence results are consistent with these predictions. In fact, the results of bicoherence analysis reveal that higher order radial modes of the drift wave are interacting with the azimuthal mode through the observed kinetic feature in the spectrum for low pressure case. For increased ionneutral collision frequency, this nonlinear interaction is replaced with harmonic mode coupling of the azimuthal modes,
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