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Reflection coefficients and excitation efficiency of a gridded plate (a bipolar potential structure where the grid is separate but parallel to the juxtaposed plate) and a metallic disk for ion-acoustic waves have been measured experimentally. When the grid is biased negatively with respect to the plasma potential, reflection in phase with the incident wave and excitation of an outgoing wave are observed only when the bias of the plate is positive. When the bias of the gridded plate is positive, reflection occurs when the grid bias is either negative or positive. For the metal disk, reflection and excitation are observed when the bias is positive. The small reflection detected when the bias is negative is found to be due to scattering of the incident wave at the edge of the disk.
Articles you may be interested inLaser-induced surface cleaning of molybdenum field emitter arrays for enhanced electron emissionThe emission uniformity of Si field emitter arrays ͑FEAs͒ with 1024 tips were evaluated by using electrostatic lens projector. Some surface modifications were applied to the Si FEA for improving the emission uniformity. A combination of CHF 3 plasma and preheat treatments is very effective for cleaning the tip surface and for improving the uniformity of the work function distribution in the array. The number of working tips increased by a factor of 5 after the preheat treatment at the temperature of 450°C. For further improvement, high current pulses were applied to the FEA. The pulse drive is effective for improving the uniformity of the tip radius. By applying all of the treatment and driving methods, more than half of the array emitters could be activated even for small operating current of 5 A.
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