| Abstrakt: |
Development and stability of heavy ion ring beams created by high speed neutral atom injection in the Earth's ionosphere is analyzed in view of the upcoming space measurement of a rocket-released turbulence (SMART) mission. It is found that due to velocity dispersion of the injected neutral atoms, an ensemble of ion ring beams will be formed at a given location upon photoionization. Associated with the multiple-ion ring beams, various beam and lower-hybrid (LH) waves develop. Wave dispersion analysis indicates that the beam energy is extracted through double resonances with beam and LH modes (i.e., ω ∼ k v r ∼ ω l h , where ωlh is the LH frequency, k is the wavenumber, and vr is the ring mean speed). For the SMART experimental conditions, we find that, far from the release point, the velocity spacing between the ion ring beams Δ v will be much less than the mean speed of the beams themselves, vr. Therefore, we show that the system will behave essentially as if represented by a single ring with an effective alpha (α) parameter (a ratio of ring to background plasma density), that is larger by a factor that is equal to N, the total number of rings. A major difference from the traditional single beam analysis is that for the more realistic multiple beam case, the effective instability is more intense because the wave growth rate now scales as ∼ (N α) 2 / 5 . [ABSTRACT FROM AUTHOR] |
