Patent Publication Number: US-2010128848-A1

Title: X-ray tube having liquid lubricated bearings and liquid cooled target

Description:
BACKGROUND OF THE INVENTION 
     This disclosure relates generally to x-ray generation systems, and more particularly to an x-ray tube having liquid lubricated bearings and a liquid cooled anode target assembly. 
     An x-ray tube generally includes a cathode assembly and an anode assembly disposed within a substantially evacuated vacuum vessel. The vacuum vessel is situated within a chamber defined by an outer casing. The outer casing may be lined with lead to shield and prevent any extraneous x-rays from straying from the x-ray tube. The chamber may be filled with a heat absorbing cooling fluid such as, for example, a dielectric oil. During operation of the x-ray tube, the cooling fluid is circulated through the chamber by a pump. The circulating cooling fluid absorbs heat from the vacuum vessel and other components of the x-ray tube, preventing damage thereto. The vacuum vessel is constructed to endure very high temperatures. 
     The cathode assembly is positioned at some distance from the anode assembly, and a voltage difference is maintained therebetween in order to extract and accelerate electrons from the cathode assembly towards the anode assembly. This voltage differential generates an electric field gradient having a strength defined by the voltage differential between the anode assembly and cathode assembly divided by the distance therebetween. 
     The anode assembly typically includes a cylindrical rotor built into a cantilevered shaft that supports a rotatable anode target. A stator coupled to a motor surrounds the rotor and causes rotation of the anode target via the rotor. A seal assembly seals the anode target within the vacuum vessel to substantially keep the vacuum vessel hermetically sealed. The anode target is typically mounted on a bearing assembly that allows rotation of the anode target by the motor. The bearing assembly typically includes ball bearings positioned within raceways. A dry metal lubricant or a liquid metal lubricant may be used on the ball bearings to increase the life of the bearings. The anode target includes a target track that is generally fabricated from a refractory metal with a high atomic number, such as tungsten, molybdenum, niobium, tantalum, rhenium, or alloys thereof. The cathode assembly typically includes a cathode emitter situated opposite the anode target within the vacuum vessel that emits electrons in the form of an electron beam that are accelerated toward the anode target and impact the target track of the anode target at a high velocity. As the electrons impact the target, the kinetic energy of the electrons is converted to high-energy electromagnetic radiation, or x-rays. The x-rays are directed out of the x-ray tube through an x-ray transmissive window in the x-ray tube housing. The x-rays are then transmitted through an object being imaged and intercepted by a detector that forms an image of the object&#39;s internal anatomy, contents or structure. 
     The impact of electrons on the target track of the anode target produces a significant amount of thermal energy that typically results in very high temperatures within the vacuum vessel of the x-ray tube. Because of these high temperatures, the anode target is typically rotated at a high rotational speed. In addition, the anode target and bearing assembly must have sufficient heat dissipation capability. 
     Current anode targets without direct cooling have the limitation of dissipating enough heat under higher power applications. Future imaging systems may require an x-ray tube with higher power capabilities. These higher power applications will likely create even higher temperatures within the vacuum vessel of the x-ray tube. It may be difficult for current anode targets to be used for higher power applications since the target track of the anode target may crack or melt under higher temperatures. 
     Future imaging systems may also require an x-ray tube with higher load capabilities. A higher load capability will increase stress on the bearing assembly. Current bearing assemblies are typically lubricated with a dry metal lubricant or a liquid metal lubricant. These lubricants may provide insufficient lubrication and insufficient cooling of the bearing assembly and anode target, and thereby may limit the life of the anode target and bearing assembly under higher power and higher load applications. 
     Therefore, there is a need for a system and method that provides the anode target and bearing assembly of an x-ray tube with increased lubrication and cooling to withstand higher power, higher temperature and higher load applications. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with an aspect of the disclosure, an x-ray tube comprising a liquid cooled anode target; and a liquid lubricated bearing assembly. 
     In accordance with an aspect of the disclosure, an x-ray tube comprising at least one vacuum vessel forming a substantially evacuated vacuum chamber; an anode assembly disposed at least partially within the vacuum chamber; a cathode assembly disposed at least partially within the vacuum chamber and spaced apart from the anode assembly; the anode assembly comprising a rotatable anode target mounted to a rotatable bearing assembly housing; an end cap coupled around a first end of the rotatable bearing assembly housing, the end cap forming a closed end at the first end of the rotatable bearing assembly housing; a stationary shaft; and at least one bearing assembly coupled between an outer surface of the stationary shaft and an inner surface of the rotatable bearing assembly housing; the x-ray tube further comprising at least one ferrofluidic seal coupled to an outer surface on a second end of the rotatable bearing assembly housing for sealing the rotatable bearing assembly housing within the vacuum chamber; at least one opening extending through the stationary shaft; a gap formed between the outer surface of the stationary shaft and the inner surface of the rotatable bearing assembly housing; and a flow path for circulating a liquid coolant and lubricant through the at least one opening, the gap, and the at least one bearing assembly. 
     In accordance with an aspect of the disclosure, an x-ray tube anode assembly comprising a stationary shaft; at least one bearing assembly coupled around the stationary shaft; a rotatable bearing assembly housing coupled around the at least one bearing assembly; a rotatable anode target mounted to the rotatable bearing assembly housing; an end cap coupled around a first end of the bearing assembly housing forming a closed end thereof; a second end of the rotatable bearing assembly housing coupled to a drive assembly for rotating the rotatable bearing assembly housing and the rotatable anode target; at least one ferrofluidic seal coupled to the second end of the rotatable bearing assembly housing; at least one opening extending through the stationary shaft; a gap formed between the stationary shaft, the end cap and the rotatable bearing assembly housing; a flow path for circulating a liquid coolant and lubricant through the at least one opening, the gap, and the at least one bearing assembly. 
     In accordance with an aspect of the disclosure, an x-ray tube anode assembly comprising a stationary shaft; at least one bearing assembly coupled around the stationary shaft; a rotatable bearing assembly housing coupled around the at least one bearing assembly; a rotatable anode target mounted to the rotatable bearing assembly housing; an open end member coupled around a first end of the bearing assembly housing; a second end of the rotatable bearing assembly housing coupled to a drive assembly for rotating the rotatable bearing assembly housing, the rotatable anode target, and the open end member; a first ferrofluidic seal coupled to the second end of the rotatable bearing assembly housing; a second ferrofluidic seal coupled to the open end member; a gap formed between the stationary shaft and the rotatable bearing assembly housing and the open end member; a flow path for circulating a liquid coolant and lubricant through the gap and the at least one bearing assembly. 
     Various other features, aspects, and advantages will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary embodiment of an x-ray imaging system; 
         FIG. 2  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube; 
         FIG. 3  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube; 
         FIG. 4  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube; 
         FIG. 5  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube; 
         FIG. 6  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube; and 
         FIG. 7  is a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings,  FIG. 1  illustrates a block diagram of an exemplary embodiment of an x-ray imaging system  10  designed both to acquire original image data and to process the image data for display and/or analysis. It will be appreciated by those skilled in the art that this disclosure is applicable to different types of x-ray imaging systems implementing an x-ray tube, such as radiography, mammography, and vascular imaging systems. Other imaging systems such as computed tomography (CT) systems and digital radiography (RAD) systems may also benefit from this disclosure. The following discussion of x-ray imaging system  10  is merely an example of one such implementation and is not intended to be limiting in terms of modality. 
     As shown in  FIG. 1 , x-ray imaging system  10  includes an x-ray source  12  configured to project a beam of x-rays  14  through an object  16  and towards a detector  18 . Object  16  may include human beings, animals, pieces of baggage, or other objects desired to be scanned. X-ray source  12  may include a conventional x-ray tube producing x-ray photons possessing a wide energy spectrum. The x-ray beam  14  generated by x-ray source  12  passes through object  16  and, after being attenuated by object  16 , impinges upon detector  18 . The detector  18  converts x-ray photons received on its surface to lower energy photons, and subsequently to electrical signals that represent the intensity of the impinging x-ray beam, and hence the attenuated x-ray beam, as it passes through object  16 . The electrical signals are transmitted to a computer  20 . 
     The computer  20 , including at least one processor  22  and associated memory  24 , receives the electrical signals from detector  18  and generates images corresponding to the internal anatomy, contents, or structure of the object  16  being imaged. The at least one processor  22  may carry out various functionality in accordance with routines stored in the associated memory  24 . The associated memory  24  may also serve to store configuration parameters, operational logs, raw and/or processed image data, and so forth. 
     The computer  20  may be coupled to a range of external devices via a communications interface. The computer  20  communicates with an operator workstation  26  to enable an operator (not shown), using operator workstation  26 , to control the imaging parameters and to view the acquired images. The operator workstation  26  includes some form of operator interface, such as a keyboard, mouse, joystick, touch enabled device, voice activated controller, or any other suitable input device (not shown) that allows an operator to control the x-ray imaging system  10  and view reconstructed images or other data from computer  20  on a display  28 . Additionally, operator workstation  26  allows an operator to store acquired images in at least one storage device  30 , which may include hard drives, tape drives, floppy discs, compact discs (CDs), digital versatile discs (DVDs), flash memory storage devices, universal serial bus (USB) storage devices, FireWire® storage devices, network storage devices, etc. The operator may also use workstation  26  to provide commands and instructions to computer  20  for controlling operation of an x-ray source controller  32  that provides power and timing signals to x-ray source  12 . The computer  20  is coupled to x-ray source controller  32 , which in turn is coupled to x-ray source  12  for controlling operation of x-ray source  12 . 
     The x-ray tube within x-ray source  12  of x-ray imaging system  10  includes a multilayer assembly providing high x-ray radiation shielding, high backscattered electron absorption, high temperature operation, and high durability. 
     In a typical vacuum environment, an anode target usually has very poor heat dissipation capability, and a bearing assembly has very poor reliability. This disclosure provides various embodiments as shown in  FIGS. 2-7  for new anode assembly designs where the anode target is cooled with a liquid and the bearings of a bearing assembly are lubricated with the same liquid to improve reliability of the anode target and bearing assembly. In an exemplary embodiment, the liquid functions as a liquid coolant and lubricant. The liquid lubricated bearings and liquid cooled anode target ensure that a bearing assembly has a long life and high load capability, and an anode target is able to dissipate more heat. This increases the x-ray tube capacity for higher power, higher loads and increases the life of the x-ray tube. 
       FIG. 2  illustrates a cross-sectional schematic diagram of an exemplary embodiment of a portion of an x-ray tube, typically called an x-ray tube insert  40 . The x-ray tube insert  40  includes at least one vacuum vessel  42  having a frame  44  and forming a substantially evacuated vacuum chamber  46  therein. The at least one vacuum vessel  42  is constructed to endure very high temperatures and includes an anode assembly  48  and a cathode assembly  50 , which are at least partially disposed therein. The anode assembly  48  includes a rotatable anode target  52  mounted to a first end  54  of a rotatable bearing assembly housing  56 . The anode assembly  48  also includes an end cap  58  coupled around the first end  54  of the bearing assembly housing  56  forming a closed end  60  thereof. In an exemplary embodiment, the end cap  58  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the first end  54  of the bearing assembly housing  56 . In an exemplary embodiment, a first sealing element  62  hermetically seals the end cap  58  to the first end  54  of the bearing assembly housing  56 . A second end  64 , opposite the first end  54 , of the rotatable bearing assembly housing  56  is coupled to a drive assembly  66  for rotating the rotatable bearing assembly housing  56  and in turn rotating the rotatable anode target  52  at a very high angular velocity. The rotatable bearing assembly housing  56  and anode target  52  attached thereto rotate around a stationary shaft  68  through the use of at least one bearing assembly  70  surrounding the stationary shaft  68 . In an exemplary embodiment, a second sealing element  72  hermetically seals the second end  64  of the rotatable bearing assembly housing  56  to the drive assembly  66 . 
     In an exemplary embodiment, the at least one bearing assembly  70  includes a first bearing assembly  74  and a second bearing assembly  94 . In an exemplary embodiment, the first bearing assembly  74  is positioned between an outer surface  114  of the stationary shaft  68  and an inner surface  116  of the bearing assembly housing  56 . In an exemplary embodiment, the second bearing assembly  94  is also positioned between the outer surface  114  of the stationary shaft  68  and the inner surface  116  of the bearing assembly housing  56  remote from the first bearing assembly  74 . 
     In an exemplary embodiment, a first groove  118  may be formed in the outer surface  114  of the shaft  68  near the first end  54  and a corresponding second groove  120  may be formed in the inner surface  116  of the bearing assembly housing  56  to hold the at least one bearing assembly  70  therein. In an exemplary embodiment, a spacer element  122  may be positioned around the shaft  68  between the first bearing assembly  74  and the second bearing assembly  94 . A fastener  124  may be located at the end of the shaft  68  and positioned against the first bearing assembly  74  to hold the at least one bearing assembly  70  in place. In an exemplary embodiment, a washer  126  may be positioned between the at least one bearing assembly  70  and the fastener  124 . In an exemplary embodiment, the fastener  124  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the end of the shaft  68 . 
     In an exemplary embodiment, the first bearing assembly  74  is a duplex bearing assembly. The first bearing assembly  74  includes a stationary inner race  76  and a rotatable outer race  78  with at least one bearing element  80  positioned between the stationary inner race  76  and the rotatable outer race  78 . Although the stationary inner race  76  and the rotatable outer race  78  are shown in  FIG. 2  as multi-race elements, the stationary inner race  76  and the rotatable outer race  78  may be formed as single race elements. 
     The stationary inner race  76  is positioned adjacent to the outer surface  114  of the stationary shaft  68 . The inner race  76  is comprised of a first inner race element  82  and a second inner race element  84 . These two inner race elements  82 ,  84  preferably do not contact each other such that an axial gap  86  is formed therebetween. The rotatable outer race  78  is positioned adjacent to the inner surface  116  of the bearing assembly housing  56 . The outer race  78  is comprised of a first outer race element  88  and a second outer race element  90 . These two outer race elements  88 ,  90  preferably do not contact each other such that an axial gap  92  is formed therebetween. A first at least one bearing element  83  is positioned between the first inner race element  82  and the first outer race element  88 . A second at least one bearing element  85  is positioned between the second inner race element  84  and the second outer race element  90 . 
     In an exemplary embodiment, the second bearing assembly  94  is a duplex bearing assembly. The second bearing assembly  94  includes a stationary inner race  96  and a rotatable outer race  98  with at least one bearing element  100  positioned between the stationary inner race  96  and the rotatable outer race  98 . Although the stationary inner race  96  and the rotatable outer race  98  are shown in  FIG. 2  as multi-race elements, the stationary inner race  96  and the rotatable outer race  98  may be formed as single race elements. 
     The stationary inner race  96  is positioned adjacent to the outer surface  114  of the stationary shaft  68 . The inner race  96  is comprised of a first inner race element  102  and a second inner race element  104 . These two inner race elements  102 ,  104  preferably do not contact each other such that an axial gap  106  is formed therebetween. The rotatable outer race  98  is positioned adjacent to the inner surface  116  of the bearing assembly housing  56 . The outer race  98  is comprised of a first outer race element  108  and a second outer race element  110 . These two outer race elements  108 ,  110  preferably do not contact each other such that an axial gap  112  is formed therebetween. A first at least one bearing element  103  is positioned between the first inner race element  102  and the first outer race element  108 . A second at least one bearing element  105  is positioned between the second inner race element  104  and the second outer race element  110 . 
     During operation of the x-ray tube, the vacuum vessel frame  44  and the shaft  68  are stationary, while the bearing assembly housing  56 , end cap  58  and anode target  52  rotate around the stationary shaft  68 . 
     The anode target  52  is sealed within the vacuum chamber  46  of the vacuum vessel frame  44  by a ferrofluidic seal  130 . A ferrofluidic seal generally includes a magnet and two pole pieces. Typically, the magnet is an annular, or hollow cylindrical, permanent type magnet that is axially polarized. Per convention, the magnet is positioned about a housing so as to encircle the housing without physically touching the housing. The two pole pieces, in turn, are typically annular as well and generally comprise magnetically permeable material. As such, the two pole pieces sandwich (i.e., abut) the magnet at the magnet&#39;s two pole ends so that the inner surfaces of the annular-shaped pole pieces respectively both face and encircle the outer surface of the housing, thereby forming (i.e., defining) a close-proximity annular-shaped gap about the housing. In such a configuration, the magnet is able to establish a desired magnetic flux path both in and about the housing for thereby concentrating and retaining ferrofluid in a seal-tight manner in the annular gap about the housing. The ferrofluidic seal  130  is positioned outside of the vacuum chamber  46  between the vacuum vessel frame  44  and the bearing assembly housing  56  to seal the anode assembly  48  within the vacuum chamber  46 . The ferrofluidic seal  130  encircles the bearing assembly housing  56  forming a hermetic seal around the bearing assembly housing  56  to maintain a vacuum within the vacuum chamber  46 . The ferrofluidic seal  130  serves as a barrier to the passage of gas along an outer surface  132  of the bearing assembly housing  56  at the second end  64  thereof, while at the same time permitting rotation of the bearing assembly housing  56  as desired. 
     The stationary shaft  68  includes at least one opening  134  extending therethrough creating a hollow shaft. In addition, a gap  136  is formed between the stationary shaft  68 , end cap  58  and bearing assembly housing  56  extending through the at least one bearing assembly  70 . The at least one opening  134  and gap  136  provides a path  138  as shown by arrows  140  for a liquid coolant and lubricant to flow. The liquid coolant and lubricant enters the anode assembly  48  through an inlet  142  in the opening  134  extending through shaft  68 , flows around the outside of the shaft  68  and inside of the bearing assembly housing  56  through the at least one bearing assembly  70 , and exits through an outlet  144  in the gap  136  between the shaft  68  and the bearing assembly housing  56  to cool the anode target  52  and lubricate and cool the at least one bearing assembly  70 . In an exemplary embodiment, the liquid coolant and lubricant may be circulated through the at least one opening  134  and gap  136  between the shaft  68  and the bearing assembly housing  56  through the at least one bearing assembly  70  by a pump (not shown). In an exemplary embodiment, the inlet  142  and the outlet  144  may be coupled to a reservoir of liquid coolant and lubricant and coupled to the pump for circulating the liquid coolant and lubricant through the flow path  138 . 
     The liquid coolant and lubricant functions both as a coolant for cooling the anode target and as a lubricant and coolant for lubricating and cooling the at least one bearing assembly  70 . In an exemplary embodiment, the liquid coolant and lubricant may be a dielectric oil. In an exemplary embodiment, the liquid coolant and lubricant may be a bearing oil lubricant, such as a mineral oil or a synthetic oil. 
     In an exemplary embodiment, the at least one bearing assembly  70  may include duplex bearings, angular contact bearings, tapped roller bearings, or needle bearings. 
     In an exemplary embodiment, the flow path  138  direction of the liquid coolant and lubricant as indicated by arrows  140  in  FIG. 2  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
       FIG. 3  illustrates a cross-sectional schematic diagram of an exemplary embodiment of an x-ray tube insert  146 . The x-ray tube insert  146  includes at least one vacuum vessel  42  having a frame  44  and forming a substantially evacuated vacuum chamber  46  therein. The at least one vacuum vessel  42  is constructed to endure very high temperatures and includes an anode assembly  148  and a cathode assembly  50 , which are at least partially disposed therein. The only difference between the x-ray tube insert  146  shown in  FIG. 3  from the x-ray tube insert  40  shown in  FIG. 2  is the configuration of the at least one bearing assembly  150  within the anode assembly  148 . The anode assembly  148  shown in  FIG. 3  includes one pair of angular contact bearings, while the anode assembly  48  shown in  FIG. 2  includes two pairs of duplex bearings. 
     The at least one bearing assembly  150  includes a first bearing assembly  152  and a second bearing assembly  162 . The first bearing assembly  152  includes a stationary inner race  154  and a rotatable outer race  156  with at least one bearing element  158  positioned between the stationary inner race  154  and the rotatable outer race  156 . The second bearing assembly  162  includes a stationary inner race  164  and a rotatable outer race  166  with at least one bearing element  168  positioned between the stationary inner race  164  and the rotatable outer race  166 . 
     In an exemplary embodiment, the first and second bearing assemblies  152 ,  162  may be tapped roller bearings or needle bearings. 
     In an exemplary embodiment, the flow path  138  direction of the liquid coolant and lubricant as indicated by arrows  140  in  FIG. 3  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
       FIG. 4  illustrates a cross-sectional schematic diagram of an exemplary embodiment of an x-ray tube insert  170 . The x-ray tube insert  170  includes at least vacuum vessel  42  having a frame  44  and forming a substantially evacuated vacuum chamber  46  therein. The at least one vacuum vessel  42  is constructed to endure very high temperatures and includes an anode assembly  172  and a cathode assembly  50 , which are at least partially disposed therein. The only difference between the x-ray tube insert  170  shown in  FIG. 4  from the x-ray tube insert  40  shown in  FIG. 2  is the configuration of the anode assembly  172 . The anode assembly  172  shown in  FIG. 4  includes a stationary shaft  174  having a first opening  176  extending through the length of the shaft  174  from a first end  178  to a second end  180 , the second end  180  being opposite the first end  178 , and a second opening  182  extending from a sidewall  184  of the shaft  174  through the first end  178  of the shaft. The first and second openings  176 ,  182  through the shaft  174  and the gap  136  formed between the stationary shaft  174 , end cap  58  and bearing assembly housing  56  extending through the at least one bearing assembly  70  provide a path  186  as shown by arrows  188  for a liquid coolant and lubricant to flow. A sealing element  190 , such as an o-ring, is used to hermetically seal the gap  136  between the bearing assembly housing  56  and the stationary shaft  174  at the second end  64  of the rotatable bearing assembly housing  56 . 
     The liquid coolant and lubricant enters the anode assembly  172  through an inlet  192  in the first opening  176  extending through shaft  174 , flows around the outside of the shaft  174  and inside of the bearing assembly housing  56  through the at least one bearing assembly  70 , in the second opening  182  in the sidewall  184  of the shaft  174 , and exits through an outlet  194  in the first end  178  of the shaft  174  to cool the anode target  52  and lubricate and cool the at least one bearing assembly  70 . In an exemplary embodiment, both the inlet  192  and the outlet  194  are through the first end  178  in the shaft  174 . 
     In an exemplary embodiment, the at least one bearing assembly  70  may include duplex bearings, angular contact bearings, tapped roller bearings, or needle bearings. 
     In an exemplary embodiment, the flow path  186  direction of the liquid coolant and lubricant as indicated by arrows  188  in  FIG. 4  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
       FIG. 5  illustrates a cross-sectional schematic diagram of an exemplary embodiment of an x-ray tube insert  196 . The x-ray tube insert  196  includes at least one vacuum vessel  42  having a frame  44  and forming a substantially evacuated vacuum chamber  46  therein. The at least one vacuum vessel  42  is constructed to endure very high temperatures and includes an anode assembly  198  and a cathode assembly  50 , which are at least partially disposed therein. The only difference between the x-ray tube insert  196  shown in  FIG. 5  from the x-ray tube insert  170  shown in  FIG. 4  is the configuration of the anode assembly  198 . The anode assembly  198  shown in  FIG. 5  includes a stationary shaft  200  having a first opening  202  extending through the length of the shaft  200  from a first end  204  to a second end  206 , the second end  206  being opposite the first end  204 , a second opening  208  extending from a sidewall  210  of the shaft  200  through the first end  204  of the shaft, and a third opening  212  extending from the sidewall  210  of the shaft  200  to the first opening  202  extending through the first and second ends  204 ,  206  of the shaft. The anode assembly  198  further includes a nozzle  222  coupled to the second opening  208  and extending through the spacer element  122  between the first bearing assembly  74  and the second bearing assembly  94  for cooling the anode target  52 . In an exemplary embodiment, the nozzle  222  may be a jet spray nozzle. 
     The first, second and third openings  202 ,  208 ,  212  through the shaft  200 , and the gap  136  formed between the stationary shaft  200 , end cap  58  and bearing assembly housing  56  extending through the at least one bearing assembly  70  provide a path  214  as shown by arrows  216  for a liquid coolant and lubricant to flow. A sealing element  190 , such as an o-ring, is used to hermetically seal the gap  136  between the bearing assembly housing  56  and the stationary shaft  200  at the second end  64  of the rotatable bearing assembly housing  56 . 
     The liquid coolant and lubricant enters the anode assembly  198  through an inlet  218  in the first end  204  of the shaft  200  through the second opening  208 , flows through the nozzle  222 , flows around the outside of the shaft  200  and inside of the bearing assembly housing  56  through the at least one bearing assembly  70 , through the first and third openings  202 ,  212 , and exits through an outlet  220  in first opening  202  in the first end  204  of the shaft  200  to cool the anode target  52  and lubricate and cool the at least one bearing assembly  70 . In an exemplary embodiment, both the inlet  218  and the outlet  220  are through the first end  204  in the shaft  200 . 
     In an exemplary embodiment, the at least one bearing assembly  70  may include duplex bearings, angular contact bearings, tapped roller bearings, or needle bearings. 
     In an exemplary embodiment, the flow path  214  direction of the liquid coolant and lubricant as indicated by arrows  216  in  FIG. 5  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
       FIG. 6  illustrates a cross-sectional schematic diagram of an exemplary embodiment of an x-ray tube insert  224 . The x-ray tube insert  224  includes at least one vacuum vessel  226  having a frame  228  and forming a substantially evacuated vacuum chamber  230  therein. The at least one vacuum vessel  226  is constructed to endure very high temperatures and includes an anode assembly  232  and a cathode assembly  50 , which are at least partially disposed therein. The anode assembly  232  includes a rotatable anode target  52  mounted to a first end  54  of a rotatable bearing assembly housing  56 . The anode assembly  232  also includes an open end member  234  coupled around the first end  54  of the bearing assembly housing  56 . In an exemplary embodiment, the open end member  234  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the first end  54  of the bearing assembly housing  56 . In an exemplary embodiment, a first sealing element  62  hermetically seals the open end member  234  to the first end  54  of the bearing assembly housing  56 . A second end  64 , opposite the first end  54 , of the rotatable bearing assembly housing  56  is coupled to a drive assembly  66  for rotating the rotatable bearing assembly housing  56  and in turn rotating the rotatable anode target  52  at a very high angular velocity. The rotatable bearing assembly housing  56  and anode target  52  attached thereto rotate around a stationary shaft  236  through the use of at least one bearing assembly  150  surrounding the stationary shaft  236 . In an exemplary embodiment, the stationary shaft  236  is a solid shaft. In an exemplary embodiment, a second sealing element  72  hermetically seals the second end  64  of the rotatable bearing assembly housing  56  to the drive assembly  66 . 
     The at least one bearing assembly  150  includes a first bearing assembly  152  and a second bearing assembly  162 . The first bearing assembly  152  includes a stationary inner race  154  and a rotatable outer race  156  with at least one bearing element  158  positioned between the stationary inner race  154  and the rotatable outer race  156 . The second bearing assembly  162  includes a stationary inner race  164  and a rotatable outer race  166  with at least one bearing element  168  positioned between the stationary inner race  164  and the rotatable outer race  166 . 
     The anode target  52  is sealed within the vacuum chamber  230  of the vacuum vessel frame  228  by a first ferrofluidic seal  238  coupled to the second end  64  of the bearing assembly housing  56  and a second ferrofluidic seal  240  coupled to the open end member  234 . 
     During operation of the x-ray tube, the vacuum vessel frame  228  and the shaft  236  are stationary, while the bearing assembly housing  56 , open end member  234  and anode target  52  rotate around the stationary shaft  236 . 
     The anode assembly  232  further includes a gap  242  formed between the stationary shaft  236  and the bearing assembly housing  56 , and the open end member  234  extending through the at least one bearing assembly  150 . The gap  242  provides a path  244  as shown by arrows  246  for a liquid coolant and lubricant to flow. The liquid coolant and lubricant enters the anode assembly  232  through an inlet  248  in the gap  242  between the shaft  236  and the open end member  234 , flows through the at least one bearing assembly  150  and exits through an outlet  250  in the gap  242  between the shaft  236  and the second end  64  of the bearing assembly housing  56  to cool the anode target  52  and lubricate and cool the at least one bearing assembly  150 . In an exemplary embodiment, the inlet  248  and the outlet  250  are at opposite ends of the x-ray tube insert  224 . 
     In an exemplary embodiment, the liquid coolant and lubricant may be circulated through the gap  242  by a pump (not shown). In an exemplary embodiment, the inlet  248  and the outlet  250  may be coupled to a reservoir of liquid coolant and lubricant and coupled to the pump for circulating the liquid coolant and lubricant through the flow path  244 . 
     In an exemplary embodiment, the first and second bearing assemblies  152 ,  162  may be tapped roller bearings or needle bearings. 
     In an exemplary embodiment, the flow path  244  direction of the liquid coolant and lubricant as indicated by arrows  246  in  FIG. 6  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
       FIG. 7  illustrates a cross-sectional schematic diagram of an exemplary embodiment of an x-ray tube insert  252 . The x-ray tube insert  252  includes at least one vacuum vessel  254  having a frame  256  and forming a substantially evacuated vacuum chamber  258  therein. The at least one vacuum vessel  254  is constructed to endure very high temperatures and includes an anode assembly  260  and a cathode assembly  50 , which are at least partially disposed therein. The anode assembly  260  includes a rotatable anode target  52  mounted to a first end  322  of a rotatable bearing assembly housing  312 . The anode assembly  260  also includes an end cap  262  coupled around the first end  322  of the bearing assembly housing  312  forming a closed end  324  thereof. In an exemplary embodiment, the end cap  262  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the first end  322  of the bearing assembly housing  312 . In an exemplary embodiment, a first sealing element  62  hermetically seals the end cap  262  to the first end  322  of the bearing assembly housing  312 . A second end  326 , opposite the first end  322 , of the rotatable bearing assembly housing  312  is coupled to a drive assembly  66  for rotating the rotatable bearing assembly housing  312  and in turn rotating the rotatable anode target  52  at a very high angular velocity. The rotatable bearing assembly housing  312  and anode target  52  attached thereto rotate around a stationary shaft  306  through the use of at least one bearing assembly  286  surrounding the stationary shaft  306 . In an exemplary embodiment, a second sealing element  72  hermetically seals the second end  326  of the rotatable bearing assembly housing  312  to the drive assembly  66 . 
     The end cap  262  includes a cantilevered shaft  264  extending outwardly from the closed end  324  thereof towards the vacuum vessel frame  256 . At least one bearing assembly  268  is coupled between the end of the cantilevered shaft  264  and the vacuum vessel frame  256  to support the cantilevered shaft  264  and prevent shaft deflection. The at least one bearing assembly  268  includes a stationary inner race  270  and a rotatable outer race  272  with at least one bearing element  274  positioned between the stationary inner race  270  and the rotatable outer race  272 . In an exemplary embodiment, the at least one bearing assembly  268  may be a solid lubricated bearing assembly. In an exemplary embodiment, the at least one bearing assembly  268  may be a tapped roller bearing or a needle bearing. 
     In an exemplary embodiment, a groove  276  may be formed in an outer surface  278  of the cantilevered shaft  264  to hold the at least one bearing assembly  268  therein. 
     A fastener  280  may be located at the end of the cantilevered shaft  264  and positioned against the at least one bearing assembly  268  to hold the at least one bearing assembly  268  in place. In an exemplary embodiment, a washer  282  may be positioned between the at least one bearing assembly  268  and the fastener  280 . In an exemplary embodiment, the fastener  280  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the end of the cantilevered shaft  264 . 
     In an exemplary embodiment, at least one bearing assembly  286  is positioned between an outer surface  328  of the stationary shaft  306  and an inner surface  330  of the bearing assembly housing  312 . In an exemplary embodiment, a first groove  332  may be formed in the outer surface  328  of the shaft  306  near the first end  322  and a corresponding second groove  334  may be formed in the inner surface  330  of the bearing assembly housing  312  to hold the at least one bearing assembly  286  therein. A fastener  124  may be located at the end of the shaft  306  and positioned against the at least one bearing assembly  286  to hold the at least one bearing assembly  286  in place. In an exemplary embodiment, a washer  126  may be positioned between the at least one bearing assembly  286  and the fastener  124 . In an exemplary embodiment, the fastener  124  may be a bolted, brazed, screwed, soldered, welded, or otherwise mechanically attached to the end of the shaft  306 . 
     In an exemplary embodiment, the at least one bearing assembly  286  is a duplex bearing assembly. The at least one bearing assembly  286  includes a stationary inner race  288  and a rotatable outer race  290  with at least one bearing element  292  positioned between the stationary inner race  288  and the rotatable outer race  290 . Although the stationary inner race  288  and the rotatable outer race  290  are shown in  FIG. 7  as multi-race elements, the stationary inner race  288  and the rotatable outer race  290  may be formed as single race elements. 
     The stationary inner race  288  is positioned adjacent to the outer surface  328  of the stationary shaft  306 . The inner race  288  is comprised of a first inner race element  294  and a second inner race element  296 . These two inner race elements  294 ,  296  preferably do not contact each other such that an axial gap  298  is formed therebetween. The rotatable outer race  290  is positioned adjacent to the inner surface  330  of the bearing assembly housing  312 . The outer race  290  is comprised of a first outer race element  300  and a second outer race element  302 . These two outer race elements  300 ,  302  preferably do not contact each other such that an axial gap  304  is formed therebetween. A first at least one bearing element  295  is positioned between the first inner race element  294  and the first outer race element  300 . A second at least one bearing element  297  is positioned between the second inner race element  296  and the second outer race element  302 . 
     During operation of the x-ray tube, the vacuum vessel frame  256  and the shaft  306  are stationary, while the bearing assembly housing  312 , end cap  262  and anode target  52  rotate around the stationary shaft  306 . 
     The anode target  52  is sealed within the vacuum chamber  258  of the vacuum vessel frame  256  by a ferrofluidic seal  130 . The ferrofluidic seal  130  is positioned outside of the vacuum chamber  258  between the vacuum vessel frame  256  and the bearing assembly housing  312  to seal the anode assembly  260  within the vacuum chamber  258 . The ferrofluidic seal  130  encircles the bearing assembly housing  312  forming a hermetic seal around the bearing assembly housing  312  to maintain a vacuum within the vacuum chamber  258 . The ferrofluidic seal  130  serves as a barrier to the passage of gas along an outer surface  328  of the bearing assembly housing  312  at the second end  326  thereof, while at the same time permitting rotation of the bearing assembly housing  312  as desired. 
     The stationary shaft  306  includes at least one opening  308  extending therethrough creating a hollow shaft. In addition, a gap  310  is formed between the stationary shaft  306 , end cap  262  and bearing assembly housing  312  extending through the at least one bearing assembly  268 . The at least one opening  308  and gap  310  provides a path  314  as shown by arrows  316  for a liquid coolant and lubricant to flow. The liquid coolant and lubricant enters the anode assembly  260  through an inlet  318  in the opening  308  extending through shaft  306 , flows around the outside of the shaft  306  and inside of the bearing assembly housing  312  through the at least one bearing assembly  268 , and exits through an outlet  320  in the gap  310  between the shaft  306  and the bearing assembly housing  312  to cool the anode target  52  and lubricate and cool the at least one bearing assembly  268 . In an exemplary embodiment, the liquid coolant and lubricant may be circulated through the at least one opening  308  and gap  310  between the shaft  306  and the bearing assembly housing  312  through the at least one bearing assembly  268  by a pump (not shown). In an exemplary embodiment, the inlet  318  and the outlet  320  may be coupled to a reservoir of liquid coolant and lubricant and coupled to the pump for circulating the liquid coolant and lubricant through the flow path  314 . 
     The liquid coolant and lubricant functions both as a coolant for cooling the anode target  52  and as a lubricant and coolant for lubricating and cooling the at least one bearing assembly  268 . In an exemplary embodiment, the liquid coolant and lubricant may be a dielectric oil. In an exemplary embodiment, the liquid coolant and lubricant may be a bearing oil lubricant, such as a mineral oil or a synthetic oil. 
     In an exemplary embodiment, the flow path  314  direction of the liquid coolant and lubricant as indicated by arrows  316  in  FIG. 7  may be reversed. 
     In an exemplary embodiment, the anode target  52  may be hollow, allowing the liquid coolant and lubricant to flow through the anode target  52 . 
     This x-ray tube insert design allows the anode target to handle much higher heat and power without having to change the anode target material. Hence this design provides a higher power anode target without the use of new anode target materials. 
     Several embodiments are described above with reference to drawings. These drawings illustrate certain details of exemplary embodiments that implement the apparatus, assemblies, systems, and methods of this disclosure. However, the drawings should not be construed as imposing any limitations associated with features shown in the drawings. 
     In various embodiments, an anode assembly for an x-ray tube is described. However, the embodiments are not limited and may be implemented in connection with different applications. The application of the disclosure can be extended to other areas both industrial and medical, for example medical imaging; diagnostic and therapeutic radiology; semiconductor manufacture and fabrication; material analysis and testing; industrial inspection; security scanning; and particle accelerators, etc. 
     While the disclosure has been described with reference to various embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the disclosure. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the disclosure as set forth in the following claims.