Advanced space charge limited field emission cathodes.

Several novel field emission cathodes are constructed by attaching a variety of materials to a steel substrate using multiple methods of bonding. These cathodes are tested using a pulsed relativistic (350-550 kV) vircator in a space charge limited operating regime. The viability of these cathodes as advanced or alternative components in high power microwave systems is evaluated.

Brazed carbon fiber fabric field emission cathode.

Field emission cathodes, comprised of commercially available carbon fiber fabrics directly brazed to metal substrates, were fabricated and tested. Cathodes fabricated in this manner eliminate the need for an epoxy bond between the carbon fibers and the substrates and can be baked, in a vacuum, at high temperatures, limited by the re-melt temperature of the braze. Preliminary testing at mildly relativistic voltages (200 kV-300 kV) yielded average current emission densities of 100's of A/cm, which are in line with previously published results on epoxy-bonded carbon fiber field emission cathodes.