Evaporation of tungsten from the filament can deposit on the window of the glass envelope and may cause which issue?

• A. Arcing and tube puncture
• B. Increased image sharpness
• C. Decreased exposure time
• D. Improved beam quality

Answer: (A)

When tungsten from the filament evaporates and settles on the glass envelope window, it creates a thin conductive layer inside the tube. This conductive spot disrupts the high-voltage vacuum conditions and can establish leakage paths between the filament and other components. Under operation, these pathways promote electrical arcing, a sudden discharge that can generate intense heat and stress on the glass. The resulting arc can damage and eventually puncture the envelope, leading to failure of the tube.

The other outcomes wouldn’t follow from tungsten deposition. It wouldn’t improve image sharpness, reduce exposure time, or enhance beam quality; in fact, it would likely degrade image quality and reliability due to compromised vacuum and potential tube damage.