Investigations of dielectric-rod focusing for traveling-wave tubes
Abstract
Relativistic electron-beam experiments by others have shown that thousands of amperes of field-emission beam current can be strongly contained and guided along the surface of a dielectric rod in vacuum. The report describes experiments to adapt this method to one-ampere, 8 to 15 kV electron beams to be used in military applications of traveling-wave tubes. Results indicate that a plasma flare forms along the dielectric rod due to field emission induced breakdown. Electron emission occurs from the plasma at the end of the rod due to lateral conductivity of the plasma surrounding the dielectric rod. The dielectric rod acts as an extension of the cathode. This proposed explanation rules out the use of a dielectric rod as a focusing device within the microwave circuit, but the dielectric rod could possibly be useful for forming and guiding the beam to the entrance of the circuit. A titanium film electrode was used as a low-voltage trigger mechanism to initiate the plasma discharge. Such a trigger device can be used to eliminate a high-voltage high-power modulator and also to achieve consistent triggering from pulse to pulse.
- Publication:
-
Naval Research Lab. Report
- Pub Date:
- June 1976
- Bibcode:
- 1976nrl..reptV....S
- Keywords:
-
- Focusing;
- Traveling Wave Tubes;
- Dielectrics;
- Electron Beams;
- Electrostatics;
- Field Emission;
- Space Charge;
- Electronics and Electrical Engineering