Question

Describe working of Reflex Klystron amplifier with a neat diagram.

Answer 1

Operation:

It is assumed that the oscillations are set up in the tube initially due to noise or switching transients and these oscillations are sustained by device operation.

The RF voltage that is produced across the gap by the cavity oscillations act on the electron beam to cause velocity modulation. The reference electron taken as the one that passes the gap on its way to the repeller at the time when the gap voltage is zero and going negative. This electron is unaffected, overshoots the gap and is ultimately returned to it having penetrated some distance into the repeller space. The early electron e_e that passes the gap before the reference electron, experiences a positive voltage at the gap. This electron is accelerated and moves with greater velocity and penetrates deep into repeller space. This electron will take slightly greater time than the reference electron to return to the gap. The late electron el that passes through the gap later than reference electron experiences negative voltage at the gap. This electron is retarded and shortens its stay in the repeller space and will return earlier to the gap as compared to the reference electron. So, the late electron will be able to catch up with e_e and e_r electrons forming the bunch. Bunches occur once per cycle centered on the reference electron. These bunch transfer maximum energy to the gap to get sustained oscillations.