In cathode ray tube display technologies, in which device do flood guns bombard the phosphor surface to maintain a stored image?

Introduction / Context:
Understanding classic CRT technologies helps explain how early displays stored or refreshed images. This question focuses on the unique flood gun mechanism that continuously bathes the phosphor or storage layer to retain a picture without constant redraw by a refresh controller.

Given Data / Assumptions:

• The question distinguishes among several CRT types.
• We focus on the image retention mechanism rather than modern flat panels.
• Terminology such as flood gun and storage layer is standard in display history texts.

Concept / Approach:

A direct view storage tube uses a writing gun to create a charge pattern on a storage target, while a separate flood gun emits low energy electrons that uniformly illuminate the target. The stored charge pattern modulates the flood electrons so that the image persists for long periods without a full refresh cycle, unlike raster or vector refresh displays.

Step-by-Step Solution:

Verification / Alternative check:

Technical descriptions of DVSTs consistently mention a writing gun plus flood gun architecture that differs from raster scan and vector refresh tubes.

Why Other Options Are Wrong:

Raster scan CRT depends on frame refresh timing. Refresh vector and stroke CRTs use beam deflection commands and lack flood gun based storage. 'None of the above' is incorrect because DVST matches the description.

Common Pitfalls:

Confusing the need for persistence phosphors in raster CRTs with the charge storage mechanism in DVSTs.

Final Answer:

Direct view storage tube