Beam Focusing Carbon Nanotube Cathode for Traveling Wave Tubes

ABSTRACT: Gigahertz microwave amplifiers are limited when using thermionic type electron sources, due to the high beam currents and frequencies required. For this reason, field emission cathodes using carbon nanotubes are being investigated as a potential electron source replacement. Such devices are capable of up to Terahertz frequencies by direct field emitter gate modulation. Busek proposes to develop methods for depositing carbon nanotube catalyst materials on curved surfaces, while approaching current densities of 10A/cm^2. Curved emission surfaces allow for focusing of emission from a larger surface, into a narrow, high current density beam, without the drawbacks of electron beam focusing. Current technology employs lithography techniques, which are not suitable for patterning on non-planar surfaces. Under the Phase I, Busek shall demonstrate micron sized catalyst patterning and perform proof-of-concept testing on a new method for generating 100nm sized catalyst"dots"for the purpose of growing individual nanotubes. All methods will be compatible with writing on curved surfaces. To improve electron beam convergence, the PECVD process used by Busek shall be modified to align carbon nanotube growth to a focal point, minimizing radial electron energies and enabling reduced beam diameter. BENEFIT: For the armed services, realization of millimeter wave radio amplifiers enables Gigabit rate point-to-point satellite communications, as well as access to currently unused spectrum, while significantly reducing amplifier mass and size. Furthermore, millimeter wave radio communications enable reduced antenna size and increased signal directionality, increasing effective signal gain to the target. Higher power versions than proposed here are also applicable to directed energy weapons. Reduced mass and volume would be critical to small forward deployable weapons systems. Commercial applications for EHF radio tend to focus on taking advantage of the 60GHz oxygen absorption signal loss for measurement of upper atmosphere temperatures.