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Physics, Techniques and Procedures

Filament

the electron source part of the cathode in an X ray tube. The X-ray tube filament is made of coiled tungsten wire which is surrounded by a metallic cup for the focusing of the electron beam onto the anode focal spot. When made of 0.2 mm thin tungsten wire, it is coiled to the form of a spiral of about 2 mm in diameter and 10 mm in length. It is heated incandescent with the filament heating current coming from the filament circuit, resulting in the production of an electron cloud by thermionic emission. Frequently in diagnostic X-ray tubes, there are two filament wires in the cathode, each in its own focusing cup (double focus tube). See also residual space charge.

AK