Portable accelerator based X-ray source for active interrogation systems

Abstract

In embodiments, a linac electron beam excited X-ray source weighing less than 50 pounds, and having a volume less than 1 cubic foot, injects electrons from an RF-excited, diamond tip cathode into a dielectric accelerator tube of diameter less than 10 mm, where the electrons are RF-accelerated to 1-4 MeV. A focusing channel having a plurality of annular permanent magnets can surround the dielectric tube, and a vacuum can be maintained in the tube by a getter pump. The accelerating RF can be 10 GHz or higher. The X-ray source can be powered by a rechargeable battery for more than an hour. Embodiments can be transported within a case having a display attached to an interior surface of its lid. An X-ray head can be removed from the case and extended up to 10 feet while remaining interconnected with the case by a flexible conduit.

Claims

1. An X-ray source comprising: a cathode configured to emit electrons when RF energy is applied to the cathode; a dielectric accelerator comprising: an accelerator tube formed from a dielectric material and having an outer diameter of less than 10 mm, the accelerator tube having a low energy input and a high energy output, said low energy input being in vacuum communication with the cathode and being configured to accept the electrons emitted from the cathode; a magnetic focusing channel surrounding the accelerator tube; an RF source configured to apply RF energy to the accelerator tube, said RF energy having a mode and phase velocity configured to cause the electrons emitted by the cathode to be accelerated so as to become high energy electrons of between 100 keV and 4 MeV as they travel within the accelerator tube from the low energy input to the high energy output, said RF energy being applied by the RF source simultaneously to the cathode and to the accelerator tube, so that the electrons are emitted by the cathode only when they will also be accelerated within the accelerator tube; a target in vacuum communication with the high energy output of the accelerator tube and configured to emit X-rays when impacted by the high energy electrons; and a power supply configured to provide all power requirements of the X-ray source; the X-ray source having a total weight of less than 100 pounds.

2. The X-ray source of claim 1, wherein the X-ray source has a total weight of not more than 50 pounds.

3. The X-ray source of claim 1, wherein the X-ray source has a total volume of not more than two cubic feet.

4. The X-ray source of claim 1, wherein the X-ray source has a total volume of not more than one cubic foot.

5. The X-ray source of claim 1, further comprising a case configured to contain the entire X-ray source in a storage configuration.

6. The X-ray source of claim 5, wherein the accelerator tube is included in an X-ray head module, which is configured to be removed from the case while retaining interconnections through a flexible conduit with a remaining portion of the X-ray source in the case.

7. The X-ray source of claim 5, wherein the case comprises a display affixed to an interior surface of a lid of the case.

8. The X-ray source of claim 1, wherein the X-ray source is configured to accelerate electrons emitted by the cathode so that the electrons become high energy electrons of at least 1 MeV as they travel through the accelerator tube.

9. The X-ray source of claim 1, wherein the power supply is a rechargeable battery, and the X-ray source further comprises a modulator configured to convert energy from the battery into high voltage pulses directed to the RF source.

10. The X-ray source of claim 1, wherein the cathode comprises a plurality of diamond tips having largest dimensions of between 1-10 nm, said diamond tips being configured to emit electrons when irradiated by the RF energy from the RF source.

11. The X-ray source of claim 1, wherein the magnetic focusing channel comprises a plurality of annular permanent magnets surrounding the accelerator tube.

12. The X-ray source of claim 1, further comprising a getter pump configured to maintain a vacuum within the accelerator tube.

13. The X-ray source of claim 1, wherein the accelerator tube has an interior diameter that is uniform, and an exterior diameter that is varied along its length in a manner that is configured to maintain a match between the phase velocity of the applied RF within the accelerator tube and the electrons as they are accelerated through the accelerator tube by the applied RF.

14. The X-ray source of claim 1, wherein an entire outer surface of the accelerator tube is metalized.

15. The X-ray source of claim 14, wherein vacuum and electromagnetic seals are provided at both the input and output ends of the accelerator tube without braised joints.

16. The X-ray source of claim 1, wherein the RF energy applied by the RF source to the accelerator tube has an RF frequency of at least 10 GHz.

17. The X-ray source of claim 1, wherein the RF source includes an X-band 200-250 kW peak air traffic control radar magnetron.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a perspective view drawn to scale of an embodiment of the present invention shown packed in a suitcase;

(2) FIG. 1B is a perspective view drawn to scale of the embodiment of FIG. 1A shown with the X-ray head module removed and placed in front of the suitcase;

(3) FIG. 2 is a perspective view drawn to scale of a compact X-ray head module according to an embodiment of the invention that includes a DLA;

(4) FIG. 3 is a sectional view drawn to scale of a cathode integrated, brazeless, low energy dielectric accelerator (DLA) in an embodiment of the invention;

(5) FIG. 4A is a cross sectional drawing that illustrates the implementation of a vacuum seal without a brazed joint in embodiments of the present invention; and

(6) FIG. 4B is a magnified sectional view drawn to scale of a portion of the view of FIG. 3, shown as inverted about the vertical axis for better comparison with FIG. 4A.

DETAILED DESCRIPTION

(7) As discussed above, the present invention is a lightweight, low cost, battery-powered, electron beam linear accelerator (linac) driven X-ray system that can be provided as a single module, can be carried by a technician, and can fit into tight spaces.

(8) FIG. 1A is a perspective view that illustrates an embodiment of the X-ray system (100) of the present invention in its storage mode, whereby the entire X-ray system is contained in one reusable, transportable case that can be carried by a single person, referred to herein generically as a suitcase 102, whereas FIG. 1B is a perspective view of the same embodiment when configured in its operation mode, wherein the X-ray head assembly (101), which includes the DLA and is separately housed, has been removed from the suitcase 102 so that it can be placed near the target (not shown). The X-ray head 101 is linked to the other, supporting modules 103 of the system, which remain inside the suitcase 102, via a long, soft cable (not shown) which provides the high voltage that is required by the X-ray head 101. The supporting modules (103) inside the suitcase 102 include the high voltage modulator, the control unit, and the battery pack, among others. A display unit (104) is mounted inside of the lid of the suitcase 102.

(9) Referring to FIG. 2, the portable X-ray head (101) includes a low energy dielectric accelerator assembly (201), referred to herein as a DLA, as well as a magnetron (202) that provides high power RF pulses to drive the DLA. A circulator (203) is installed at the output of the magnetron to protect the magnetron from damage in case it is subject to a full power reflection out of the DLA, for example during the rising and falling edges of an RF pulse, or due to an RF breakdown during operation. The X-ray head (101) further includes a compact directional coupler that monitors the forwarding and reflected RF pulse signal.

(10) The RF pulses that are produced by the magnetron (202) cause the electrons that are emitted from the cathode 307 of the DLA (201) to gain kinetic energy as they pass through the DLA. Once the energetic electrons reach the exit of the DLA, they are stopped by a thin film target (not shown) made of a selected material or materials, which can be or can include tungsten and/or titanium. The collision of the energetic electrons with the atoms of the target material create an X-ray flux, which is known as Bremsstrahlung radiation.

(11) Referring to FIG. 3, the low energy dielectric accelerator assembly (201) (DLA) includes a standing wave dielectric tube (301), a focusing channel (302) surrounding the dielectric tube that includes a plurality of spaced apart permanent magnets, a shielding and support pipe (303), a high power RF window (304), an RF coupler (305), a getter pump (306), a cathode insert (307), and a vacuum gate (308).

(12) Embodiments include any combination of several power saving features that help to reduce size, weight, and power requirements, so that the embodiment can be deployed as a battery powered unit without an external power supply. For example, the cathode which emits the electrons can be a field emission cathode that incorporates a plurality of diamond tips, each of which has a largest dimension of between 1 and 10 nanometers. When high power RF is applied to the cathode, the diamond tips continuously emit electrons. As such, no external heating element is needed to create the cathode electron emissions, as would be the case with a conventional, thermally heated cathode. Furthermore, the emitted electrons are naturally emitted in concentrated bursts that are spaced apart according to the period of the applied RF waves, and therefore enter the DLA only when the RF is present and able to accelerate them. In embodiments, the cathode is part of a cathode insert (307), which is designed in embodiments to be easily replaceable when it wears out.

(13) The focusing channel 302 reduces beam losses at the initial stages of acceleration. Rather than implementing one or more electrically excited solenoids to guide the electron beam through the dielectric accelerator, which is the traditional approach, embodiments of the present invention reduce power consumption by implementing a focusing channel (302) that includes a series of periodically spaced-apart, annular permanent magnets that surround the accelerator tube, and generate a strong magnetic focusing field without requiring any electrical power. Implementation of this permanent magnet focusing channel is rendered feasible and cost-effective due to the significant reduction in transverse size of the DLA, as compared to traditional metallic accelerators.

(14) Initially, the vacuum within the DLA is established, for example during its manufacture, by using an external pumping station, after which the gate (308) is closed. At that point, a getter pump (306), which does not require power once it is activated, is used to maintain the vacuum inside the DLA.

(15) The RF coupler (305) is used to efficiently convert the electromagnetic mode in the waveguide into the accelerating mode in the DLA. In embodiments, the RF coupler also includes two accelerating gaps that rapidly extract electrons from the cathode and accelerate them to the injection energy that the DLA requires.

(16) With reference to FIG. 4A, in embodiments the vacuum seal of the DLA can be established without using a brazing process. Instead, the outer surface of the dielectric tube (401) is metalized, usually by copper, except the end surface at the lower energy side (which has a thicker dielectric wall). The lower energy side is then soldered to a copper gasket (402) using a low temperature solder at around 200 C. The solder joint is sealed at the tip of the gasket (403), which is inserted into the RF coupler (405) so as to couple the electromagnetic waves from the coupler into the dielectric tube 401, and also so as to accept the injected electrons from the cathode. A knife edge (404) is formed at the RF coupler side. When the metal tube of the RF coupler (405) is pushed against the copper gasket 402 during assembly, the knife edge bites into the copper gasket 402 to seal the vacuum.

(17) FIG. 4B is a magnified sectional view drawn to scale of a portion of the view of FIG. 3, shown as inverted about the vertical axis for better comparison with FIG. 4A.

(18) The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure.

(19) Although the present application is shown in a limited number of forms, the scope of the invention is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof. The disclosure presented herein does not explicitly disclose all possible combinations of features that fall within the scope of the invention. The features disclosed herein for the various embodiments can generally be interchanged and combined into any combinations that are not self-contradictory without departing from the scope of the invention. In particular, the limitations presented in dependent claims below can be combined with their corresponding independent claims in any number and in any order without departing from the scope of this disclosure, unless the dependent claims are logically incompatible with each other.