Modulation of field emission by small AC signals

In a microwave tube the energy of electrons in an electron beam, which are usually generated by a thermionic cathode, is modulated such that it is transformed into electromagnetic wave energy. In this paper, we modulated the field emission using AC signals. A field emission current with AC components was attained by adding a small AC voltage to a high extracting DC voltage. We observed two phenomena related to the AC components of the field emission current. First, when the DC component of the extracting voltage was low, the current measured in the circuit was dominated by the displacement current. Second, besides the fundamental frequency component, higher order harmonics were also observed in the field emission current.