We consider the possibility of taking advantage of nonlinear character of the Fowler-Nordheim emission law for generation of a bunched electron beam in a resonant cavity. Interaction of electron bunches, accelerated by an electrostatic field in the cavity, with the cavities eigenmodes allows for energy transfer from the e-beam to the electromagnetic field, facilitating generation of radiation. In particular, we are targeting coherent electromagnetic wave generation in the THz range. A simplified model, in absence of space charge effect, shows that in a deep saturation regime a superposition of dc and harmonic electric field in the cavity wold produce field-emitted current density which within an excellent approximation can be represented by a Gaussian profile. For high current densities, space charge effect cannot be ignored and an accurate estimation of the current density spatial/temporal distribution requires a self-consistent solution of a nonlinear electromagnetic problem. We present the latest progress of this research.