Ionospheric Interaction Experiments With Gigawatts

High power HF transmitters have induced a number of plasma instabilities in the interaction region of overdense ionospheric plasma. We report results from the first such experiments to use over one gigawatt of HF power (ERP) in comprehensive studies of strong Langmuir turbulence (SLT) and particle acceleration. Among the effects observed and studied are: SLT spectra including the outshifted plasma line or free-mode, appearance of a short timescale ponderomotive overshoot effect, artificial field-aligned irregularities (AFAI), the aspect angle dependence of the intensity of the plasma line, and suprathermal electrons. We explore the observed magnetic-zenith effect of enhanced turbulence backscatter with the HF pump wave directed up the field line. Experimental results are compared to previous high latitude experiments and predictions from recent modeling efforts.