Fluctuation Noise Due to Collision Ionization in Electronic Amplifier Tubes

Ions formed by collision in electronic amplifier tubes move toward the cathode and control‐grid and produce momentary increases in the space‐charge limited current (current pulses). These current pulses are random in time and produce fluctuation noise analogous to the shot‐effect. An approximate theory is presented, applicable to cathodes of large diameter (ca. 0.1 cm). Both the noise and the increase in the average value of the electron current due to the presence of ionization are calculated in terms of the ``size of the elementary event'' or the integral of the current pulse. It is not feasible to calculate the latter directly but it may be evaluated indirectly by measurements of the increase of average current. The noise calculated from the values so obtained and from the ionization probability data of Smith, Bleakney and Tate is in close agreement with that observed experimentally. The production of noise in tubes with oxide cathodes containing mercury vapor, argon and the gases naturally evolved fro...