Operation of a carbon fiber cathode

Summary form only given, as follows. We present results of an experimental investigation of a cathode made of carbon fibers. We studied the operation of a carbon fiber cathode having emitting area of 20 cm/sup 2/ and of 100 cm/sup 2/ as well as the emission properties of an individual carbon fiber having a diameter of 6 /spl mu/m. Experiments with large area cathodes were performed using a PFN generator with the following parameters: accelerating voltage of 250 keV, impedance of 80 /spl Omega/, and pulse duration of 250 ns. Experiments with an individual carbon fiber were performed using a 40-100 ns pulse generator having a voltage amplitude up to 20 kV. The threshold of the electron emission versus the accelerating voltage was obtained, It was shown that electron emission occurs from the plasma formed on the surface of the carbon fiber. The uniformity of the cathode plasma formation and its expansion towards the anode was studied. The electron beam uniformity with spatial and temporal resolution and its micro-divergence was obtained by the use of the X-ray image produced by electron beam interaction with a Ta-made anode and by a multi-pinhole camera, respectively. In addition, an array of collimated Faraday cups was used to obtain electron beam uniformity. Compatibility of the cathodes with vacuum requirements is presented.