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X Ray Tube Having Anode With Compound Motion

IP.com Disclosure Number: IPCOM000083043D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Gunn, JB: AUTHOR

Abstract

The limiting factor in the design of high-intensity X-ray tubes is usually the thermal loading of the target due to electron bombardment. Common ways to improve this limit are: (1) Internal water cooling of the anode so as to provide the shortest possible heat path; (2) Movement of the anode during operation, so as to spread out the area of electron impact from a spot into a ring.

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X Ray Tube Having Anode With Compound Motion

The limiting factor in the design of high-intensity X-ray tubes is usually the thermal loading of the target due to electron bombardment. Common ways to improve this limit are: (1) Internal water cooling of the anode so as to provide the shortest possible heat path; (2) Movement of the anode during operation, so as to spread out the area of electron impact from a spot into a ring.

Tubes using one or both of these techniques are avilable commercially. However, even the use of a water-cooled rotating anode is unlikely to provide adequate intensity, for the X-ray lithographic techniques now under development by industry.

In order to permit a further increase in intensity, a water-cooled anode with a compound motion is provided, so that the focal spot moves in a complicated path which overlaps very little, rather than in the ring which overlaps once per revolution as in the conventional rotating anode tube. This has the result of spreading the mean power of the electron beam over a much larger area than can be achieved by mere rotation or nutation (see Fig. 1).

Although any complex path such as a raster would serve this purpose, there are considerable advantages in using a curve compounded out of uniform circular motions, since such motions are easily generated with high velocity, and the resulting inertial forces are easily counterbalanced. The most useful such curve is probably the trochoid, since, with suitable choice of parameters, the velocity can be kept high at all points; the path can be made to cross itself at large angles (near or equal to 90 degrees); and successive crossings in the same place can be made long (infinite if the radii of the generating circles are incommensurable). All of these properties will help to reduce the amount of local dynamic heating of the anode.

Referring to Fig. 2, a simple way to generate a trochoidal path for the focal spot 1 is to have the anode 2 in the form of a disk, rotating about its own axis in a bearing 3, and to have bearing 3 itself rotating about a second axis rotating fixed in bearing 4. In this case, the rotation of anode 2 itself ensures that, with a line focus, the motion of focal spot 1 can be kept reasonably normal to the length of the spot, ensuring that its instantaneous track is kept from becoming too narrow. (If the motion is allowed to become parallel to the length of the spot, the narrowing of the track will negate most of the advantages of the compound motion). However, the rotation has a disadvantage, in that it is impossible to carry cooling water to the inside of the anode itself without using rotating seals, which require a continuously pumped tube.

This difficulty can be overcome if anode 2 is moved without rotation (Fig. 3), and metal bellows 5 can be used as a seal, permitting sealed-off operation of the tube. However, focal spot 1 now...