Experimental and Theoretical Studies of High Power Plasma Filled Backward Wave Oscillators
Progress rept. 1 Aug 1990-31 Jan 1991
MARYLAND UNIV COLLEGE PARK LAB FOR PLASMA RESEARCH
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The purpose of the research covered during this period was to study the behavior of a plasma loaded BWO when driven by large beam current approaching the vacuum space charge limiting value inside the device. The main results are 1 The plasma indeed allows injection of large current into the BWO. Currents as high as 75 of the vacuum space charge limit were successfully propagated. 2 In plasma loaded BWO, in contrast to the vacuum case, the enhanced efficiency can be maintained even for large beam currents approaching the vacuum limit. It is anticipated that this might hold even well beyond the vacuum limit. 3 The output frequency is only slightly shifted 1-5 by the presence of the plasma. 4 A foilless field emission diode can operate successfully in a background of low density plasma. 5 An important parameter, the start oscillation current was measured for the first time in vacuum BWO for various beam voltages and geometries. For example, at 600 kV the start current is under 140 A. 6 Initial indications are that the plasma increases the microwave pulse duration. 7 A novel field emission cathode design new geometries and materials allows for continuous control of the beam current in the range of 50-6000 Amps. Turn on fields below 50kVcm were achieved. 8 Linear theory for a plasma loaded BWO was developed using a simplified model. and 9 A nonlinear theory for a finite length device was developed.
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