X-ray tube target having enhanced thermal performance and method of making same
An x-ray tube includes a frame enclosing a high vacuum, a cathode positioned within the enclosure, and a target assembly. The target assembly includes a target cap, a focal track material positioned on the target cap to receive electrons from the cathode, and a foam material positioned within a cavity of the target cap and positioned proximate the focal track. The x-ray tube also includes a bearing assembly attached to the frame and configured to support the target assembly.
1. An x-ray tube comprising:
a frame enclosing a high vacuum;
a cathode positioned within the enclosure;
a target assembly comprising:
a target cap;
a focal track material positioned on the target cap to receive electrons from the cathode; and
a foam material positioned within a cavity of the target cap and positioned behind the focal track, the foam material having a directional thermal conductivity such that the thermal conductivity axially through the foam material is greater than the thermal conductivity radially through the foam material; and
a bearing assembly attached to the frame and configured to support the target assembly.
2. The x-ray tube of claim 1 wherein the foam material is carbon-based pyrolitic graphite comprising a plurality of continuous ligaments, wherein the continuous ligaments have a thermal conductivity of approximately 1700 W/m-K.
3. The x-ray tube of claim 1 wherein the foam material comprises one of carbon, silicon carbide, a refractory metal, and a ceramic.
4. The x-ray tube of claim 1 wherein the foam material comprises an open-cell foam that is impregnated with a heat storage material.
5. The x-ray tube of claim 4 wherein the heat storage material has a phase-change temperature below 900° C.
6. The x-ray tube of claim 1 wherein the foam material is in direct contact with the focal track material.
7. The x-ray tube of claim 6 wherein the foam material is in direct contact with the focal track material along an entire length of the foam.
8. The x-ray tube of claim 1 wherein the target assembly includes graphite attached to the target cap and positioned on a face of the target cap opposite a face to which the focal track material is attached.
9. The x-ray tube of claim 8 wherein the foam material is in direct contact with the graphite, with the foam material positioned between the focal track and the graphite.
10. The x-ray tube of claim 1 wherein the focal track extends radially on a focal track surface from a first target radius to a second target radius, and wherein the foam material extends radially within the cavity from proximate a bore of the target cap to between the first target radius and the second target radius.
11. The x-ray tube of claim 1 wherein the foam comprises a plurality of ligaments having a thermal conductivity along a primary directional path that is greater than a thermal conductivity in a direction orthogonal to the primary directional path, with the primary directional path parallel to a direction of the thickness of the target cap.
12. An x-ray imaging system comprising:
a detector positioned to receive x-rays that pass through an object; and
an x-ray source positioned to emit x-rays toward the object, the x-ray source comprising:
an electron emitter;
a target assembly comprising:
a target cap;
a focal track attached to the target cap and positioned to receive electrons from the electron emitter; and
a structural foam positioned within a hollow of the target cap that is positioned behind the focal track so as to enhance conduction through the thickness of the target cap, the structural foam comprising a plurality of continuous ligaments having a thermal conductivity greater than 1000 W/m-K, wherein the thermal conductivity of the plurality of continuous ligaments along a primary directional path is greater than the thermal conductivity of the plurality of continuous ligaments in a direction orthogonal to the primary directional path, the primary directional path being parallel to a direction of the thickness of the target cap; and
a bearing assembly attached to a frame of the x-ray source and configured to support the target assembly.
13. An x-ray imaging system comprising:
a detector positioned to receive x-rays that pass through an object; and
an x-ray source positioned to emit x-rays toward the object, the x-ray source comprising:
an electron emitter;
a target assembly comprising:
a target cap;
a focal track attached to the target cap and positioned to receive electrons from the electron emitter; and
a structural foam positioned within a hollow of the target cap that is positioned behind the focal track so as to enhance conduction through the thickness of the target cap, the structural foam comprising an open-cell foam that is impregnated with a heat storage material, the open cell foam comprising a plurality of ligaments having a thermal conductivity along a primary directional path that is greater than a thermal conductivity in a direction orthogonal to the primary directional path, the primary directional path being parallel to a direction of the thickness of the target cap; and
a bearing assembly attached to a frame of the x-ray source and configured to support the target assembly.
14. The x-ray imaging system of claim 13 wherein the heat storage material has a phase-change temperature below 900° C.
15. An x-ray tube comprising:
a frame enclosing a high vacuum;
a cathode positioned within the enclosure;
a target assembly comprising:
a target cap;
a focal track material positioned on the target cap to receive electrons from the cathode; and
a foam material positioned within a cavity of the target cap, the foam material comprising a plurality of ligaments having a thermal conductivity along a primary directional path that is greater than a thermal conductivity in a direction orthogonal to the primary directional path, the primary directional path being parallel to a radial direction of the target cap; and
a bearing assembly attached to the frame and configured to support the target assembly.