Method for Determination of Normalized Intrinsic Emittance of Cold Emission Cathodes

  Miron Voin  ,  Miron Voin [1]  ,  Levi Schachter [1]  
[1] Technion

We consider a method for determination of normalized intrinsic emittance of cold emission cathodes. While in principle we are motivated primarily by carbon-nanotube (CNT) cathodes, our approach is applicable to any type of cold cathode. Its essence relies on evaluation of the initial momentum as the particles tunnel through the Schottky-Nordheim barrier based on the spectral radiance function. Next, the momentum distribution is integrated over the geometry, providing, along with well known Fowler-Nordheim current, an integral expression for the emittance. It is shows that the normalized emittance of a single emitter is proportional to the normalized Fermi velocity of the emitter material, transverse dimension of the emitter, and the square root of applied local electric field. According to our theoretical results and based on experimental data for CNT emitters available in the literature, we predict that practical cold emission cathodes may provide a normalized intrinsic emittance comparable or even superior to that of conventional photo-emission cathodes used in state-of-the-art electron sources.