Heater Beam Angle Effect on Simulated Brillouin Scatter in Magnetized Ionospheric Plasma

High power electromagnetic waves transmitted from HAARP have recently been shown to excite low frequency electrostatic waves by magnetized stimulated Brillouin scatter MSBS near the reflection or upper hybrid resonance regions. The pump wave may excite either electrostatic ion acoustic wave (IA) or electrostatic ion cyclotron wave (EIC) waves. Whether IA and EIC waves are excited depends on the wave propagation relative to the ambient magnetic field. It had been confirmed that only ion acoustic waves are observed for propagation near magnetic zenith while EIC waves can only be observed with more oblique propagation angles. The original discovery of EIC waves excited by the MSBS process considered only a narrow range of heater beam angles. The EIC wave strength in the spectrum was observed to be highly variable and proposed to possibly be near threshold. Also observations of the upshifted EIC waves in the spectrum were almost nonexistent. This was true for cascading of the downshifted EIC lines as well. Those EIC spectrum lines can provide valuable diagnostics for ion composition. This experiment conducted at the 2010 HAARP Summer School aims to look more thoroughly at a broader range of heater beam angle effects on IA and EIC waves generated by MSBS in the F layer ionosphere. The expected results show that the stronger IA and EIC spectrum lines were observed by the O-mode excitation. With increasing tilting angles, there exists a critical heater power beam angle above that EIC modes appear in the lower SEE spectrum. The power spectrum of EIC is more sensitively affected by the power beam angle than the IA spectrum lines. The experiments also aim to observe the second EIC (or even higher) frequency downshifted harmonics generated with increasing tilting angle.