Which microwave device employs a helix slow-wave structure to achieve wideband interaction with an electron beam?

Introduction / Context:
Slow-wave structures reduce the phase velocity of RF waves to interact efficiently with electron beams. Recognizing device architectures is essential in microwave engineering.

Given Data / Assumptions:

• Helix supports a slow traveling wave over a broad bandwidth.
• Electron beam interacts continuously along the helix for amplification.

Concept / Approach:
The traveling-wave tube (TWT) uses a helical slow-wave structure to achieve near-constant phase velocity over a wide frequency range, enabling broad bandwidth gain. By contrast, klystrons use resonant cavities (buncher, catcher) and do not rely on a helix.

Step-by-Step Solution:

Verification / Alternative check:
Any microwave textbook shows cross-sections: TWT with helix winding around the beam tunnel; klystrons with cavities.

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer: