X-ray generation

Abstract

An apparatus for generating x-rays includes an electron beam generator and a first device arranged to apply an RF electric field to accelerate the electron beam from the generator. A photon source is arranged to provide photons to a zone to interact with the electron beam from the first device so as to generate x-rays via inverse-Compton scattering. A second device is arranged to apply an RF electric field to decelerate the electron beam after it has interacted. The first and second devices are connected by RF energy transmission means arranged to recover RF energy from the decelerated electron beam as it passes through the second device and transfer the recovered RF energy into the first device.

Claims

1. An apparatus for extracting energy from a particle beam comprising: a particle beam generator; a first superconducting device arranged to apply an electric and/or magnetic field to accelerate the particle beam; an arrangement configured to extract energy from the accelerated particle beam through an interaction process; a second superconducting device arranged to apply an electric and/or magnetic field to decelerate the particle beam after it has interacted; and a superconducting electromagnetic coupling arranged to recuperate energy from the particle beam as it passes through the second device and transfer the recuperated energy into the first device; wherein the first and second devices are arranged substantially in parallel and side-by-side; and wherein at least the first device, second device and superconducting coupling are provided together in a cryostat.

2. The apparatus of claim 1, wherein the first and second superconducting devices comprises a plurality of RF cavities in which an RF electric field is applied to accelerate/decelerate the electron beam.

3. The apparatus of claim 1, wherein the superconducting coupling arranged to recuperate energy from the particle beam comprises one or more waveguides that connect the first and second devices to transfer energy in the form of RF electromagnetic radiation.

4. The apparatus of claim 1, wherein at least one of the particle beam generator or the arrangement configured to extract energy from the particle beam is provided in the cryostat.

5. The apparatus of claim 1, wherein the particle beam comprises one or more of: electrons, positrons, protons, or ions.

6. The apparatus of claim 1, wherein the first and second devices are arranged substantially in parallel or side-by-side.

7. The apparatus of claim 1, wherein at least one of the first device or the second device is a linear accelerator.

8. The apparatus of claim 7, wherein the first device and the second device each include an axis, and the axes are arranged substantially parallel to one another.

9. The apparatus of claim 1, further comprising an arrangement configured to turn the beam substantially through 180° between the first device and the second device.

10. The apparatus of claim 9, wherein a photon source is arranged to provide photons to interact with the electron beam as the accelerated beam turns through an angle of about 90° after passing out of the first device.

11. The apparatus of claim 1, wherein: the particle beam generator is an electron beam generator; the particle beam is an electron beam; the first superconducting device is arranged to apply an RF electric field to accelerate the electron beam from the generator; the arrangement configured to extract energy from the accelerated article beam is a photon source arranged to provide photons to interact with the electron beam from the first device so as to generate x-rays via inverse-Compton scattering; the second superconducting device is arranged to apply an RF electric field to decelerate the electron beam after it has interacted; and wherein the first and second superconducting devices are connected by the superconducting electromagnetic coupling, which is an RF energy transmission coupling arranged to recover RF energy from the decelerated electron beam as it passes through the second device and transfer the recovered RF energy into the first device.

12. The apparatus of claim 11, wherein the RF energy transmission coupling comprises one or more RF waveguides connecting the first and second devices.

13. The apparatus of claim 11, wherein at least one of the first device or the second device comprises one or more RF cavities arranged in series.

14. The apparatus of claim 13, wherein each RF cavity in the second device is coupled to a corresponding RF cavity in the first device by a respective waveguide.

15. The apparatus of claim 11, wherein the first and second devices each have respective upstream and downstream ends, and wherein the downstream end of the second device is connected to the upstream end of the first device by the RF energy transmission coupling.

16. An apparatus for extracting energy from an electron beam comprising: an electron beam generator; a first device comprising a plurality of superconducting RF cavities in which an RF electric field is applied to accelerate the electron beam; an arrangement configured to extract energy from the accelerated electron beam through an interaction process; and a second device comprising a plurality of superconducting RF cavities in which an RF electric field is applied to decelerate the electron beam after it has interacted; wherein the first and second devices are connected by one or more superconducting RF waveguide(s) arranged to recover RF energy from the decelerated electron beam as it passes through the second device and transfer the recovered RF energy into the first device; wherein the first and second devices are arranged substantially in parallel and side-by-side; and wherein the superconducting RF cavities of the first and second devices and the superconducting RF waveguide(s) are provided in the same cryostat.

17. The apparatus of claim 16, wherein the interaction process comprises at least one of: interacting the electron beam with photons to generate x-rays via inverse-Compton scattering; passing the electron beam through an undulator or applying an alternating magnetic field to generate electromagnetic radiation; directing the electron beam onto a target to cause emission and/or fluorescence; or interacting the electron beam directly with a sample for electron diffractometry or microscopy.

18. The apparatus of claim 16, wherein the superconducting RF cavities of the first and second devices and the superconducting RF waveguide(s) are integrally formed or connected together.

19. The apparatus of 16, wherein the superconducting RF cavities of the first and second devices and the superconducting RF waveguide(s) are provided in the same cryostat.

20. A method for extracting energy from a particle beam comprising the steps of: generating a particle beam; passing the particle beam through a first superconducting device arranged to apply an electric and/or magnetic field to accelerate the particle beam; extracting energy from the accelerated particle beam through an interaction process; passing the particle beam through a second superconducting device arranged to apply an electric and/or magnetic field to decelerate the particle beam after it has interacted; and arranging a superconducting coupling to recuperate energy from the particle beam as it passes through the second device and transfer the recuperated energy into the first device; wherein the first and second devices are arranged substantially in parallel and side-by-side; and wherein at least the first device, second device and superconducting coupling are provided together in a cryostat.

21. The method of claim 20, wherein the particle beam includes one or more of electrons, positrons, protons, or ions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Some preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic flow diagram showing the main components in an x-ray generating apparatus according to embodiments of the present invention;

(3) FIG. 2 is a schematic diagram showing the acceleration, interaction and deceleration of a particle beam with energy recuperation according to an embodiment of the present invention;

(4) FIG. 3 is a schematic diagram showing the acceleration, interaction and deceleration of a particle beam with energy recuperation according to another embodiment of the present invention;

(5) FIG. 4 is a schematic diagram showing detail from FIG. 3 in both plan and sectional views;

(6) FIG. 5a is a schematic diagram of a cryostat module according to an embodiment of the present invention;

(7) FIG. 5b is a schematic diagram of a cryostat module according to another embodiment of the present invention;

(8) FIG. 6 is a schematic diagram of a cryostat module according to yet another embodiment of the present invention;

(9) FIG. 7 is a schematic diagram showing the acceleration and deceleration of a particle beam with energy recuperation after an interaction process according to a first embodiment of the present invention;

(10) FIG. 8 is a schematic diagram showing the acceleration and deceleration of a particle beam with energy recuperation after an interaction process according to a second embodiment of the present invention; and

(11) FIG. 9 is a schematic diagram showing the acceleration and deceleration of a particle beam with energy recuperation after an interaction process according to a third embodiment of the present invention.

DETAILED DESCRIPTION

(12) There is seen from FIG. 1 the basic components of an x-ray generating apparatus 1 depicted in the form of a flow diagram (i.e. not representative of physical layout). An electron beam is generated by an electron gun 2, typically a radiofrequency (RF) photoinjector comprising a RF power supply, a laser source and a photocathode located in a RF cavity to produce bunches of electrons when photons from the laser impact on the photocathode. Such electron guns are well known and will not be described in further detail here. The electron beam (e-beam) generated by the gun 1 may be at an initial energy Emin e.g. around 1 MeV. The electron beam enters a first linear device 4 that is arranged to accelerate the beam up to an interaction energy Emax of about 20 MeV. The accelerator 4 includes a plurality of RF accelerating cavities to which an alternating RF electric field is applied. An RF power supply (not shown) may input around 10 kW of power to drive the acceleration process.

(13) The electron beam leaving the accelerator 4 is at an energy Emax suitable for interaction. At this stage in the apparatus 1 a laser 6 is arranged to direct a photon beam to interact with the electron beam. A laser mirror cavity may provide for collisions between electron bunches and laser pulses. X-rays of keV scale are generated via inverse-Compton scattering and typically emitted in the direction of the electron beam. After the interaction, the electron beam enters a second linear device 8 that is arranged to decelerate the beam. The decelerator 8 also includes a plurality of RF cavities to which an alternating RF electric field is applied. A RF power supply (not shown) may input around 2 kW of power to drive the deceleration process. The RF energy that is given off by the electron beam as it decelerates is recuperated and transferred back to the accelerator 4 via an energy coupling 10. The de-energized electron beam that passes out of the decelerator 8 is sent to a beam dump 12.

(14) The electron beam, after deceleration, is dumped at much lower energy Emin than its maximum energy. The energy Emin at the dump can be as low as 0.1 MeV, which is 200 times less than the maximum beam energy. Correspondingly, the RF power needed to accelerate the electron beam is about two hundred times lower than the reactive power of the electron beam at the point of interaction with the laser light.

(15) A possible range of typical operating parameters is provided, for the sake of illustration, in Table 1 below.

(16) TABLE-US-00001 TABLE 1 Typical parameters, range [ ] Electron beam E, MeV 10 20 30 Electron bunch charge, nC 0.2 0.5 1 e-bunch repetition rage, MHz 50 200 1000 e-beam average current, A 0.01 0.1 1 e-beam reactive power, MW 0.1 2 30 e-beam energy at dump, MeV 0.2 0.1 0.1 laser wavelength 1000 600 300 X-ray max energy, keV 2 12 60 X-ray min wavelength, nm 0.6 0.1 0.02 X-ray flux, ray/s 1.E+15 8.E+15 4.E+16 approx peak brilliance 2.E+20 2.E+21 8.E+21 ph/(s mm{circumflex over ( )}2 mrad{circumflex over ( )}2 0.1% bw) approx RF power, kW 2 10 100 e-Energy recovery coefficient 50 200 300

(17) The energy recuperation provided by such an apparatus 1 greatly reduces the demands on the RF power supplies for the accelerator 4 and decelerator 8. It can be seen from Table 1 that the RF input to each linear device 4, 8 need only be of the order of 10 kW to produce an accelerated electron beam having an energy Emax of around 20 MeV and reactive power of, for example, 200 kW for the interaction process. The power in the beam can therefore be 200 times higher than would be possible without energy recuperation.

(18) It will be understood the block diagram in FIG. 1 does not represent the actual spatial arrangement of the components in the apparatus 1 but is merely a schematic of the energy flow. While the linear decelerator 8 may be provided on the same beam line as the linear accelerator 4, to make the apparatus 1 compact it is preferred that the linear devices 4, 8 are spatially arranged side-by-side e.g. with their axes parallel. Typically a linear accelerator/decelerator device has a length about 10 times its diameter so the determining factor for the overall size of an apparatus is usually the layout of the linear devices. A parallel arrangement of the linear devices minimizes their footprint while the energy recuperation technique enables a final beam energy Emax to be achieved with a shorter accelerator, resulting in a much more compact apparatus than previous proposals. FIGS. 2-9 depict such a compact arrangement and will now be described in more detail.

(19) FIG. 2 provides a first example of an energy recuperation arrangement. A linear accelerator 4 and a linear decelerator 8 are provided in parallel, each with its own RF input 14. It is shown schematically that the linear devices 4, 8 each have a multi-cell structure comprising a number of RF cavities 16 arranged in series along the axis of the device 4, 8. Each RF cavity 16 is a waveguide tuned to create RF standing waves. The RF field is applied to electrodes (not shown) arranged along the length of the device 4, 8.

(20) An electron (or other particle) beam enters the accelerator 4 with an initial energy Emin and exits with an interaction energy Emax. The accelerated beam is turned 180° so that it can enter the decelerator 8 after undergoing an interaction process. While the beam is being turned through the first 90° it is focused and compressed ready for interaction, for example in a laser cavity located at the 90° point in the beam's trajectory. Energy is extracted from the beam, for example in the form of x-rays generated by inverse-Compton scattering. While the beam is turned through another 90° it is de-compressed before passing into the decelerator 8. The beam may be turned by applying magnetic fields.

(21) It can be seen from FIG. 2 that energy recuperated in the decelerator 8 is transferred back into the accelerator 4 by a plurality of RF waveguides 18 that couple the cavities 16 together. As the linear devices 4, 8 are arranged side-by-side, the RF couplings 18 can be relatively short so energy losses can be minimized. FIG. 3 shows another arrangement for recuperating energy. In this example, the accelerator 4 and decelerator 8 are coupled by a single RF waveguide 18 that connects the RF cavities 16 in one device to the other. It will be appreciated that the RF coupling 18 may take any suitable form, including single or multiple waveguides, separate or joined waveguides, or other channels suitable to transfer energy from the decelerator 8 to the accelerator 4.

(22) FIG. 4 shows a cryostat module 20 in which the accelerator 4 and decelerator 8 are embedded, together with their RF input supplies 14. Although only a single RF waveguide 18 is shown coupling together the RF cavities 16, there could of course be multiple couplings 18 as seen from FIG. 2. The RF coupling waveguide 18 is also embedded in the cryostat module 20. Each of the RF components can be formed of a superconducting material with the cryostat 20 used to maintain an operating temperature of around 2 K. An advantage of integrating the accelerator 4, the decelerator 8 and the RF coupling 18 into the same cryostat module 20 is that energy losses are minimized and the RF input power can be reduced. It is seen from the sectional view in FIG. 4 that arranging the two linear devices 4, 8 side-by-side in the same cryostat 20 results in a very compact module. The RF coupling 18 between the devices 4, 8 does not necessarily take up any additional space.

(23) FIG. 5 provides some further examples of a cryostat module 20. In FIG. 5a it can be seen that both the electron gun 2 (or other particle generator) and the beam dump 12 are provided outside of the cryostat 20. The electron gun 2 may comprise a room temperature cavity or a superconducting cavity for the RF photoinjector. One advantage of using a superconducting cavity is that the electron beam can be either pulsed or continuous-wave. In FIG. 5b it can be seen that the electron gun 2, for example a superconducting photoinjector, is provided inside the cryostat 20 with the linear devices 4, 8. The beam dump 12 is kept outside the cryostat 20 to help minimise the cryo-cooling power. The built-in electron gun 2 shares the cryo-cooling with the other components so that less power is required for the superconducting components. In this case the required external RF power will be defined only by the energy to which the beam can be decelerated in the second linear device 8, while the full power of the beam at Emax can be orders of magnitude higher.

(24) FIGS. 6-9 exemplify some of the possible interaction processes for the electron (or other particle) beam as it passes between the accelerator 4 and the decelerator 8. One or more of these interaction processes may be arranged to take place in the interaction block of the flow diagram shown in FIG. 1.

(25) In FIG. 6 an array 22 of superconducting magnets is embedded is the same cryostat 20 as the linear devices 4, 8 and used to transport, focus and compress the particle beam. As is shown, the beam may pass through a laser mirror cavity 26 where it interacts with photons to generate x-rays via inverse-Compton scattering. FIG. 7 shows a different version of the layout seen in FIG. 6. Instead of superconducting magnets, an array 24 of normal magnets provides for transport, focus and compression of the particle beam before it passes through the interaction zone 26. This magnetic array 24 is located outside the cryostat 20 that houses the linear devices 4, 8 and their RF coupling 18.

(26) In FIG. 8 there is shown an alternative interaction process. Instead of using inverse-Compton scattering to generate x-rays, the energized electron beam is transported by magnets and passed through an undulator 28 so as to generate x-rays on the principle of a free electron laser. FIG. 9 shows yet another interaction process, wherein the electron beam is not used to generate x-rays but instead is used directly to study a sample 30, e.g. via electron diffraction.

(27) In all of the interaction processes described above the electron (or other particle) beam benefits from the RF energy recuperation between the decelerator and accelerator devices. Furthermore it will be appreciated that the schematic diagrams are not to scale and in reality each linear device may be of the order of 1 m long with a diameter an order of magnitude smaller. The side-by-side arrangement and integration of the linear devices can therefore provide a massive space-saving as compared to conventional linear layouts.

(28) Although the preferred embodiments have been described above in relation to an electron beam, it will be understood that various features of these embodiments may be applied to other types of charged particle beam, including proton beams and ion beams. It will be appreciated that the electron or other particle beam may also be used for numerous interaction processes beyond those described.

(29) Embodiments of the present invention have numerous industrial applications, including bio-medical applications e.g. clinical high resolution imaging and phase-contrast imaging, micro-tomography and x-ray protein crystallography, cultural/heritage applications e.g. imaging ancient artefacts, security monitoring e.g. nuclear resonance fluorescence, and extreme ultraviolet lithography.