klystron

High-power microwave vacuum-tube amplifier. Generates the RF energy that accelerates electrons in the linac waveguide.

Why it matters to buyers: Finite lifespan. Most expensive scheduled wear item on Clinac iX. Filament current drop = interlock.

Why it matters to engineers: Never bypass klystron interlocks. Arcing risks collateral damage to waveguide / circulator / bend magnet.