Gated Field Emission Cathode RF Gun

High-brightness electron beams are required for a number of applications, from advanced accelerators to 4th generation light sources. However, the current technology for producing such beams requires an expensive, complicated laser system to drive a photocathode in a radio frequency gun. This technology is difficult to extend to high duty cycles, as is necessary for many applications in research and industry. In this proposed project, a novel, gated field emission electron source using carbon nanotubes will be developed. While field emission cathodes have been under investigation for use in radio frequency guns for more than two decades, and can produce relatively low emittance for a given cathode size, they have typically either produced very low currents or are prone to damage and are unable to directly produce short pulses. This proposal addresses these issues with two innovations: the use of robust carbon nanotube films capable of producing good current density with low thermal emittance; and a novel radio frequency gun design capable of gating the emission from the cathode to pulses of less than 100 picoseconds. Combined, these innovations enable a high duty cycle, low emittance, short pulse electron source, that avoids the requirement for an expensive photocathode drive laser. In Phase I of the proposed project, the two-frequency gun was designed and simulated, and a carbon nanotube cathode was experimentally tested in a pulsed regime. The promising results have laid a strong foundation for the work follow in this Phase II project. In Phase II, the engineering will be completed and the two-frequency radio frequency gun will be fabricated. Carbon nanotube cathodes will also be optimized and tested under radio frequency power. Finally, an optimized, low-emittance gun will be fabricated and tested. Commercial Applications and Other Benefits: Besides applications in high-energy physics and next-generation light sources, the carbon nanotube cathode based gun described in this proposal could also be applied wherever thermionic cathodes are used in commercial applications, such as in medical radiotherapy linacs, cargo inspection linacs, and industrial irradiation systems. The gated carbon nanotube cathode gun would produce better beam quality, reduce the cost, and potentially increase the reliability of such systems.