Reflex klystron oscillator – Potential of the focusing electrode Consider the focusing electrode used to shape and confine the electron beam near the cathode in a reflex klystron. Is this electrode normally held at a high potential compared to the cathode?

Introduction:
A reflex klystron is a microwave oscillator in which an electron beam emitted by the cathode is velocity-modulated at a cavity gap, then turned back by a negatively biased reflector (repeller) electrode to pass the gap again in phase with the RF. Several electrodes shape the beam near the cathode region, including a focusing electrode (or focusing anode).

Given Data / Assumptions:

• Standard reflex klystron construction with cathode, focusing electrode, resonant cavity, and negatively biased reflector.
• Goal of focusing electrode is beam shaping and confinement close to the cathode.

Concept / Approach:

The focusing electrode is typically at or near cathode potential, sometimes slightly negative relative to the cathode to compress the beam. It is not held at a high positive potential. In contrast, the reflector electrode is at a high negative potential relative to the cathode to reverse the electron beam and set the oscillation frequency through transit-time conditions.

Step-by-Step Solution:

Verification / Alternative check:

Textbook biasing diagrams show the focusing electrode tied to cathode or slightly negative, while the reflector has an adjustable high negative bias controlling mode and frequency.

Why Other Options Are Wrong:

Options C, D, and E suggest special cases that do not reflect normal design practice. The focusing electrode is not the element providing high potential; that function belongs to the reflector.

Common Pitfalls:

Confusing the focusing electrode with the reflector; assuming all control electrodes must be at high potential.

Final Answer:

False.