Optimization of the Electron Emission From Carbon Nanotubes for Electron Cooling in ELENA

Electron cooling is a process that guarantees beam quality in low energy antimatter facilities. In ELENA the electron cooler allows to reduce the emittance blow-up of the antiproton beam, thus delivering highly focused and bright beams at the unprecedented low energy of 100 keV to the experiments. In order to have a "cold" beam at such low energy, the electron gun of the cooler must emit a monoenergetic and relatively intense electron beam. Simulations have shown that efficient cooling can be achieved with a 5 mA electron beam having transverse energy spread of less than 100 meV and longitudinal energy spread of about 1 meV. A thermionic gun is currently used in operation, although it limits the performances due to a relatively high transverse energy of the emitted beam (> 100 meV). Therefore, an optimization of the ELENA e-cooler gun is currently being studied, with the aim to develop and design a cold cathode e-gun based on carbon nanotubes acting as cold electron field emitters. The use of carbon nanotube arrays for electron emission implies the need of an extracting grid in order to allow a stable and uniform emission at relatively low electric fields. The grid and its features become then critical to control the electron beam properties. In this contribution we present a simulation study of the current extraction from a field emitting material involving different extracting grid types and how they affect the beam properties. Eventually, we propose a new gun layout.