Simulation and experimental study on tungsten field emission cathode

We have been developing a tungsten field emission cathode for a Cherenkov FEL or Smith–Purcell FEL. The properties of the electron beam from a tungsten tip have been investigated using numerical simulation and some experiments. Although the 2nd gate reduced the emission current due to a decrease of the effective field at the tungsten tip, it focused and enlarged the electron beam current in a certain potential range of the 2nd gate depending on the cathode voltage and the distance between 1st and 2nd gates. The electron beam diameter was reduced to ∼2 mm on the fluorescent screen at the anode.