4.3: SWNT fiber field emission cathodes

Small diameter, high current density electron beams are needed for the small beam tunnels required for high frequency traveling wave tube (TWT) amplifiers. The Air Force Research Laboratory (AFRL) began research on small diameter (<;100μm) single fiber DC cathodes for this application. Two types of fibers were tested. Fibers made from graphite were compared to fibers made solely from single walled carbon nanotubes (SWNTs) that are densely packed and highly aligned along the axial direction. Graphite fiber cathodes suffered serious degradation due to joule heating after only 25 hours of operation while only producing up to 200μA of current. SWNT fiber cathodes produced approximately 3mA of current for hundreds of hours while showing minimal physical damage.