What component selectively focuses the electron beam toward the anode in an x-ray tube?

The component that selectively focuses the electron beam toward the anode in an x-ray tube is the cathode. The cathode is made up of a filament and a focusing cup. The filament heats up and emits electrons through thermionic emission when an electrical current passes through it. The focusing cup, which is typically made of metal, serves to shape the emitted electron beam, directing it towards a small area on the anode where the x-rays are produced. By focusing the electron beam, the cathode ensures that the x-rays produced are of high intensity and have better resolution, which is critical for obtaining quality images in radiography.

This function differentiates the cathode from the anode, which is responsible for the actual production of x-rays when the electron beam strikes it, as well as from other components like the glass envelope, which provides a vacuum environment necessary for the efficient operation of the x-ray tube, and the filament, which primarily serves to emit electrons rather than focus them.