Fluctuations in space-charge-limited currents

The paper shows that the fluctuations in the anode current of a space-charge-limited valve can be calculated in a manner exactly similar to the calculation of the thermal agitation noise in a metallic conductor, in terms of the electron transits. Corresponding values of the noise ratio, or ¿smoothing factor,¿ are derived; they are found to be in agreement with experimental data from a variety of sources. The ratio is a function of eV/(k¿), and is only slightly dependent upon the ratio of anode diameter to cathode diameter of the valve.