Final answer:
The tube filament is found on the cathode side of an X-ray tube, where it emits electrons that then generate X-rays upon interaction with the anode material.
Step-by-step explanation:
The tube filament in an X-ray machine is located on the cathode side. The cathodic side is where electrons originate, and these electrons are then accelerated toward the anode side, where they interact with the anode material to produce X-rays. This process includes bremsstrahlung radiation when electrons are decelerated, and characteristic x-rays that are unique to the material of the anode.