Extractor cup on a miniature x-ray tube
Methods for connecting electrical potential to an extractor cup at the cathode of a miniature x-ray tube are disclosed. The various connection schemes are designed to form a rugged and conveniently manufacturable connection between the metal extractor cup and one side of the cathode filament, so that the extractor cup shapes the path of electrons as desired en route to the anode of the tube. Some of the disclosed connections involve evaporation of conductive metal or other materials off the filament when the filament is first activated. Others involve applying a paste or paint conductive precursor directly to a base to connect a post and the extractor, the paste being heat-cured after the completion of assembly. Others involve a fine wire or spring strip from one filament post to the walls of the extractor cup. Other schemes include welded or brazed wires or foil, crimping, pinching, swaging and other connections, all made inside the tube enclosure.
1. In a miniature x-ray tube having a cathode with a cathode filament, an anode and an extractor cup adjacent to the cathode, a means of connecting high voltage potential to the extractor cup, comprising:
the cathode filament being supported on posts from a non-conductive cathode base, the posts being conductive and extending into the interior of the extractor cup,
the filament being pre-coated with a conductive metal precursor which will evaporate from the filament and deposit conductive material on adjacent surfaces when the filament is initially heated to a predetermined temperature,
the extractor cup comprising a hollow shape with conductive material at least on an inner surface of the extractor cup, and the extractor cup being secured to the base during assembly of the x-ray tube, and
a shield positioned on one of the filament posts to shadow an area of the base adjacent to the one post from receiving any coating from the conductive material when evaporated off the filament,
whereby after the cathode and the x-ray tube are fully assembled and evacuated, the cathode filament is heated to such predetermined temperature to evaporate the conductive precursor material to deposit the conductive material on the base and on the extractor cup, thereby connecting one side of the filament to the extractor cup via the base, so that the extractor cup will be at the high voltage potential of one side of the filament during operation of the x-ray tube.
2. The miniature x-ray tube of claim 1 , wherein the conductive metal precursor comprises gold, whereby the interior of the extractor cup becomes coated with a reflective coating and thus reduces heat loss into the extractor, reducing power required to operate the filament.
3. In a miniature x-ray tube having a cathode with a cathode filament, an anode and an extractor cup adjacent to the cathode, a means of connecting high voltage potential to the extractor cup, comprising:
the cathode filament being supported on posts from a non-conductive cathode base, the posts being conductive and extending into the interior of the extractor cup,
the filament being pre-coated with a semiconductor material which will evaporate from the filament and be deposited on adjacent surfaces when the filament is initially heated to a predetermined temperature, and
the extractor cup comprising a hollow shape with conductive material at least on an inner surface of the extractor cup, and the extractor cup being secured to the base during assembly of the x-ray tube,
whereby after the cathode and x-ray tube are fully assembled and evacuated, the cathode filament is heated to such predetermined temperature to evaporate and deposit the semiconductor material on the base and on the extractor cup, thereby connecting with semiconductor material the filament to the extractor cup via the base and posts, so that the extractor cup will be essentially at the high voltage potential of the filament during operation of the x-ray tube and excess charge buildup on the extractor cup is drained.
4. The miniature x-ray tube of claim 3 , wherein the semiconductor material as deposited on the base has a resistance of about 200,000 to 300,000 ohms, in a miniature x-ray tube having an outside diameter in the range of about 1 mm to 2 mm.