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In a three-cavity klystron amplifier, in which cavities are RF oscillations (RF fields) present and excited during normal operation?

Difficulty: Easy

Correct Answer: both (a) and (b)

Explanation:


Introduction / Context:
Klystron amplifiers use cavity resonators and electron-beam bunching to achieve high-gain microwave amplification. Understanding where RF fields exist helps clarify the amplifier mechanism.


Given Data / Assumptions:

  • Three-cavity topology: input (buncher), intermediate (idler), and output (catcher).
  • Small-signal excitation at the input; power extracted at the output.


Concept / Approach:
The input cavity is driven by the external RF signal, creating velocity modulation in the beam. After drifting and bunching (aided by the idler cavity in three-cavity designs), the bunched beam deposits RF energy into the output cavity, where oscillatory fields are sustained and power is coupled out. Therefore, oscillations (RF fields) are excited in both the input and output cavities during normal operation.


Step-by-Step Solution:

External RF excites the input cavity → velocity modulation.Beam bunches in drift region; idler cavity improves bunching and gain stability.Bunched beam induces oscillations in the output cavity → RF power output.


Verification / Alternative check:
Oscilloscope or network analyzer measurements (via weak probes) show RF fields in both input and output cavities; the idler cavity is tuned but typically not externally driven.


Why Other Options Are Wrong:

Input only or output only ignores the dual-cavity nature of excitation and extraction.Intermediate only is incorrect; it provides additional gain/tuning but is not the sole locus of oscillations.“Purely DC” is incorrect; RF cavities define the device.


Common Pitfalls:

Conflating amplifier klystrons with klystron oscillators; amplifiers require an input signal but still sustain resonant RF fields in cavities.


Final Answer:

both (a) and (b)
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