441Microwave Tubes
tubes with a focussed electron beam similar to that in CRT. In klystron, the
RF eld is stationary; thus, interaction between the beam and the RF eld
is not continuous. In TWT also, the RF eld travels with the speed of light,
while the velocity of electron beam does not exceed 10% of the speed of light,
even with very high anode voltage. Continuity of interaction between beam
and RF eld demands that these two travel in the same direction and with
almost the same velocity. TWT uses such a structure to make the interaction
continuous.
12.5.1 Simplified Model of TWT
Imagine that an electron beam emerging from an electron gun is passing along
a straight wire. This wire represents a (terminated) non-resonant transmission
line ...