Applications on high current, high brightness cathodes for microwave production, imaging, and material processing

Summary form only given. Very-high-brightness cathodes with current densities of 10/sup 4/-10/sup 6/ A/cm/sup 2/ and total current of more than a few kA have been constructed and tested. Three different cathode geometries were studied: linear cathode for sheet beams, point cathodes for conical beams, and annular cathodes for thin annular beams. Both the linear and the annular cathodes were used for microwave generation. Current from 100 A at 50 kV to a few kA at 600 kV were generated. The current density of these beams was about 10/sup 4/ A/cm/sup 2/. The sheet beam produced mm-wave radiation in a Smith-Purcell geometry and the annular beam geometry was employed in a BWO experiment with and without plasma background. A point source electron beam was used to produce electron shadowgraphy of a gas puff from a nozzle into vacuum. The beam parameters were: 200 ns long, 10 to 30 A, 15 to 40 kV, and source size less than 0.1 mm. The cathode anode distance of the point source beams at the above parameters was about 10 cm, implying that long pulses can be generated. Due to the high brightness, relatively simple electron optics can be used to collect and focus a beam on a target, which makes it an ideal candidate for electron beam processing.