Transit-Time Effect in Klystron Gaps

The theory of the klystron is usually based upon a simplified configuration in which it is assumed that the grid spacing in the buncher is so small that, during the flight of the electron through it, the electric field changes very little. This assumption leads to a certain ideal value for the drift distance S. It is of interest to calculate the effect on the ideal value of S caused by a finite spacing of the buncher grids. This calculation is carried through by means of a graphical method suggested by R. Kompfner. It is found that, in general, as the grid spacing is increased, the value of S is also increased. In the case of the depth of modulation M equal to 0.5, S is found to increase by 47 per cent as the grid spacing is varied from 0 to 2 millimeters for an accelerating voltage of 1200 volts and a frequency of 3×10⁹cycles per second.