tion across the heating and diagnostic beam. Using these improvements, agreement between theory and observations is good, as shown in Fig. 5. As a result of the experimental results and corresponding improvements in the models of heating theory, 23 mW/cm2 should no longer be considered a design limit for the SPS microwave power beam, at least with respect to the excitation of nonlinear interactions. The remaining differences at the lowest altitudes result from complications in interpreting the radar backscatter data when the local plasma Debye length and the radar wavelength become comparable. By delaying the radar diagnostic pulse with respect to the heating pulse, it was possible to measure the ionospheric cooling time scales as a function of altitude (see Fig. 6). The measurement accuracy is about a factor of two, and confirms the predictions of the electron cooling models. Although these experiments usefully provided the first test of enhanced electron heating theory, the results are limited by the restriction to 10 ms pulsed heating. As shown in the current theoretical heating predictions, this heating would not have achieved equilibrium throughout the beam.
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