Reflex klystron oscillation condition – Role of anode and repeller voltages State whether a reflex klystron oscillates only for those combinations of anode voltage and repeller (reflector) voltage that yield a favorable electron transit time through the cavity–reflector–cavity path.

Introduction:
A reflex klystron is a single-cavity oscillator that relies on velocity modulation at the cavity gap and subsequent reflection of the electron beam by a negatively biased repeller electrode. Sustained oscillation requires that bunched electrons return to the gap in the correct phase to deliver energy to the RF field.

Given Data / Assumptions:

• Single resonator (re-entrant cavity) and a repeller electrode with variable negative voltage.
• Anode voltage sets beam energy; repeller voltage sets turn-around distance/time.
• Small-signal oscillation requires loop phase and loop gain conditions (Barkhausen) to be met.

Concept / Approach:

For oscillation, the electron transit time T from the first pass through the gap, to reflection, and back to the gap must satisfy a phase condition commonly written as ωT ≈ (2πn + 3π/2) for integer n (modes often labeled n + 3/4). Only certain combinations of anode and repeller voltages produce a suitable T that yields positive power transfer to the cavity.

Step-by-Step Solution:

Verification / Alternative check:

Practical tuning curves show discrete voltage regions (modes) where output power peaks; between them, oscillation stops or weakens.

Why Other Options Are Wrong:

Claims about cryogenic temperatures, multiple resonators, or space-charge prerequisites are not fundamental to the oscillation condition in reflex klystrons.

Common Pitfalls:

Confusing the single-cavity reflex oscillator with multi-cavity klystron amplifiers; overlooking that repeller tuning controls frequency and output power via transit time.

Final Answer:

True.