X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
2000-09-07
2003-06-17
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S130000
Reexamination Certificate
active
06580780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to x-ray tube devices. In particular, embodiments of the present invention relate to a cooling system for stationary anode x-ray tubes that employs extended surfaces to increase the rate of heat transfer from the x-ray tube so as to significantly reduce heat-induced damage within the x-ray tube structure and thereby extend the operating life of the device and permit operation of the x-ray tube device at relatively higher power settings than would otherwise be possible.
2. Prior State of the Art
X-ray producing devices are extremely valuable tools that are used in a wide variety of applications, both industrial and medical. Such equipment is commonly used in applications such as diagnostic and therapeutic radiology, semiconductor manufacture and fabrication, and materials testing. While used in a number of different applications, the basic operation of x-ray tubes is similar. In general, x-rays, or x-ray radiation, are produced when electrons are produced, accelerated, and then impinged upon a material of a particular composition.
Regardless of the application in which they are employed, these devices typically include a number of common elements including a cathode, or electron source, and an anode situated within an evacuated enclosure in a spaced apart arrangement. The anode includes a target surface oriented to receive electrons emitted by the cathode. In operation, an electric current applied to a filament portion of the cathode causes electrons to be emitted from the filament by thermionic emission. The electrons thus emitted then accelerate towards a target surface of the anode under the influence of an electric potential applied between the cathode and the anode. Upon approaching and striking the anode target surface, many of the electrons either emit, or cause the anode to emit, electromagnetic radiation of very high frequency, i.e., x-rays. The specific frequency of the x-rays produced depends in large part on the type of material used to form the anode target surface. Anode target surface materials with high atomic numbers (“Z” numbers) are typically employed. The x-rays are then collimated so that they exit the x-ray tube through a window in the tube, and enter the x-ray subject. As is well known, the x-rays can be used for therapeutic treatment, x-ray medical diagnostic examination, or material analysis procedures.
As discussed above, some of the electrons that impact the anode target surface convert a substantial portion of their kinetic energy to x-rays. Many electrons, however, do not produce x-rays as a result of their interaction with the anode target surface, but instead impart their kinetic energy to the anode and other x-ray tube structures in the form of heat. As a consequence of their substantial kinetic energy, the heat produced by these electrons is significant. Still other electrons simply rebound from the target surface and strike other “non target” surfaces within the x-ray tube. These are often referred to as “backscatter” electrons. These backscatter electrons retain a significant amount of kinetic energy after rebounding, and when they impact these other non-target surfaces, heat is generated within the x-ray device. The heat generated as a consequence of electron impacts on the target surface and other x-ray device structures must be reliably and continuously removed. If left unchecked, it can ultimately damage the x-ray tube and shorten its operational life.
Some x-ray generating devices at least partially alleviate this heat problem by employing an anode that continuously rotates within the device. This rotation distributes the heat over a larger area of the anode, allowing for more efficient dispersal of heat in the x-ray tube and reducing the chances of heat damage to the device. However, some applications such as x-ray fluorescence and spectrometry in sample analysis, and product and process control in the metals and cement industries, are best performed using stationary anode x-ray generating devices. Thus, alternative approaches to cooling have been developed for use with these types of devices.
One such approach involves the use of a cooling fluid circulated within the x-ray device. An example of this approach involves circulating a cooling fluid through a passageway formed within the interior of the anode so as to remove heat conducted to the anode from the anode target surface. This process is sometimes referred to as “impinging flow heat transfer” because at least a portion of the coolant flow is caused to impinge upon, or impact, at least one of the surfaces or structures of the x-ray tube from which heat is to be removed. This approach has proven problematic in some instances however, primarily due to the cooling fluids typically employed.
A variety of cooling fluids have been used in such a stationary anode x-ray generating device cooling system. Due to the structural and operational characteristics of the x-ray device, the cooling fluid employed must possess certain characteristics. For example, the cooling fluid must have an acceptable thermal efficiency, i.e., be capable of effectively absorbing and removing the significant heat produced during operation of the x-ray device. Furthermore, the high electric potential between the cathode and the anode necessitates the use of a cooling fluid that is electrically non-conductive, or “dielectric.”
Various dielectric coolants have been employed in the context of stationary anode x-ray devices. For example, deionized water has been found to be an acceptable cooling fluid in some stationary anode x-ray generating devices because of its efficient heat absorption capabilities and non-conductivity. However, deionized water must be constantly monitored and processed to ensure that it retains its dielectric property. Such monitoring and processing increases the cost and complexity of the x-ray device cooling system. In view of the disadvantages of deionized water as a cooling fluid, alternative fluids have been utilized. For example, dielectric oils are commonly employed in stationary anode x-ray generating devices because of their non-conductivity. Further, they are somewhat more desirable than deionized water in that they do not require maintenance or processing to maintain their nonconductive properties.
While dielectric fluids are generally desirable cooling media for x-ray device applications due to their electrical properties, they have proven unable to adequately cool many stationary anode x-ray devices. Thus, a need exists for improving the rate of heat transfer that is currently achieved in typical stationary anode x-ray tubes.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or adequately solved by currently available stationary anode cooling systems. Thus it is an overall object of embodiments of the present invention to resolve at least the aforementioned problems and shortcomings in the art by providing an x-ray tube cooling system that facilitates a relative increase in the rate at which heat is transferred from x-ray tubes. Embodiments of the present invention are especially well-suited for use in the context of stationary anode x-ray tubes. However, it will be appreciated that the features and advantages of the present invention may find useful application in other types of x-ray devices as well
Briefly summarized, the foregoing objects and advantages are provided by an x-ray tube cooling system employing a surface area augmentation structure having a plurality of extended surfaces configured to transfer heat from the stationary anode and other x-ray tube structures to a liquid coolant circulating through the stationary anode.
In a preferred embodiment, the surface area augmentation structure comprises a cooling disk having an annular body defining an aperture, and a plurality of cooling fins disposed about the apert
Dunn Drew A.
Varian Medical Systems Inc.
Workman & Nydegger & Seeley
Yun Jurie
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