What are the three main components of the cathode (-) in an x-ray tube?

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The cathode is where electrons come from, and its three main pieces are the tungsten filament, the molybdenum focusing cup, and the power supply. The tungsten filament is heated by the current from the power supply, and its high temperature causes thermionic emission so electrons are released. The molybdenum focusing cup sits around the filament and uses electrostatic fields to focus and direct those electrons into a tight beam toward the anode. The power supply provides both the heater current to keep the filament hot and the high voltage to accelerate the emitted electrons toward the target. The anode and the tube’s vacuum are essential to the x-ray tube as a whole, but they’re not part of the cathode assembly itself.