aquadag coated cardboard (with fan cooling) in the plane of the horn. The key results are shown in Fig.3. The upper traces are the beam amplitude profile and the lower traces are Langmuir probe measurements of the plasma decay. Note at the 3 kW level (upper photo) the microwave beam modifies the plasma, while at 380 W and 340 mW there is no change in the plasma density produced by the e-beam. A phase shift of 75° (averaged over the 6 ms pulse) was observed between the 340 mW and 380 W power levels — evidently due to the microwave beam power modulating the plasma density and being deflected by the modulation. The measured 75° phase shift if uniform would represent doubled peak plasma density of 2 x 10$ e/cm$; since there was no appreciable change observed on the Langmuir probe characteristic, such a change apparently did not occur. Proposed Ionospheric Experiments. In the ionosphere at SPS power level, the instability growth process favors spatial wavelengths of order 50 mA, but so far diagnostic techniques have been limited to spatial resolutions of much larger scale. A new technique which is reviewed should yield high spatial resolution. Spatial gain as a function of beam power level for various spatial wavelengths can be determined by measurements of phase distribution of a microwave beam propagating upward through the underdense ionosphere. The high spatial resolution is to be accomplished by rapidly moving the detector aboard a satellite across the near field of the beam refracted by electron density striations, as shown in Fig. 4. J.E. Drummond, 4th Princeton Conf, on Space Mfg. Facilities (May 1979).
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