The tube cathode (filament) is heated with a low-voltage current of a few amps. The
filament heats up and the electrons in the wire become loosely held. A large electrical
potential is created between the cathode and the anode by the high-voltage
generator. Electrons that break free of the cathode are strongly attracted to the anode
target. The stream of electrons between the cathode and the anode is the tube
current. The tube current is measured in
milliamps and is controlled by regulating
the low-voltage heating current applied to
the cathode. The higher the temperature
of the filament, the larger the number of
electrons that leave the cathode and travel
to the anode. The milliamp or current
setting on the control console regulates
the filament temperature, which relates to
the intensity of the X-ray output.