HYBRID LINEAR ACCELERATOR WITH A BROAD RANGE OF REGULATED ELECTRON AND X-RAY BEAM PARAMETERS INCLUDES BOTH STANDING WAVE AND TRAVELING WAVE LINEAR SECTIONS FOR PROVIDING A MULTIPLE-ENERGY HIGH-EFFICIENCY ELECTRON BEAM OR X-RAY BEAM USEFUL FOR SECURITY INSPECTION, NON-DESTRUCTIVE TESTING, RADIATION THERAPY, AND OTHER APPLICATIONS

Abstract

A Hybrid (SW+TW) Linear Acellerator is disclosed having high beam efficiency and broad energy regulation that is useful for security inspection, non-destructive testing, radiotherapy, and electron beam irradiation of objects. The Hybrid Linear Accelerator (LINAC) provides superior energy regulation, and includes a reversed RF power distribution which substantially improves RF power utilization, thereby eliminating need for an output RF load, and ensuring broad electron beam energy regulation operating in a broad range of input RF power, thereby efficiently running at a variety of input electron beam current intensities at high efficiency. The Hybrid LINAC may be equipped with a fast and/or slow phase shifter and/or a power regulator having a phase shifter and a current regulator, while operating much more efficiently than known LINACS. The Hybrid LINAC permits efficient operation without an external magnetic field, thereby avoiding use of a power-consuming solenoid, consequently reducing cost of production, operation, and maintenance.

Claims

1. A Hybrid LINAC with high beam efficiency and broad energy regulation for security inspection, non-destructive testing, radiotherapy, and electron beam irradiation of objects, the Hybrid LINAC comprising: an electron gun configured to provide an input beam of electrons; a standing wave linear accelerator section (SW Buncher) configured to receive the input beam of electrons and accelerate the electrons, the SW Buncher including an SW Input RF Coupler, the SW Buncher providing an intermediate beam of accelerated electrons; a traveling wave linear accelerator section (TW accelerator) configured to receive the intermediate beam of accelerated electrons, and to further increase the momentum and energy of the accelerated electrons, the TW accelerator including a TW Input RF Coupler and a TW Output RF Coupler, the TW accelerator providing an output beam of electrons; a drift space configured to provide RF decoupling between the SW buncher and the TW accelerator, while also permitting transit of the intermediate beam of accelerated electrons from the SW buncher to the TW accelerator; an RF source configured to provide RF energy to the TW accelerator via a first RF Transmitting Waveguide and the TW Input RF Coupler; and a second RF Transmitting Waveguide including at least one of: a Switch, a Phase Shifter, and a Power Adjuster, the second RF Transmitting Waveguide being cooperative with both the TW Output RF Coupler and the SW Input RF Coupler, the second RF Transmitting Waveguide allowing the SW Buncher to serve as an adjustable resonant load so as to provide broad energy regulation of the output beam of electrons, the second RF Transmitting Waveguide also enabling the SW Buncher to be fed with RF power remaining after attenuation in the TW accelerator so as to provide high beam efficiency of the output beam of electrons.

2. The Hybrid LINAC of claim 1, wherein the standing wave linear accelerator section (SW Buncher) is cooperative with a first external magnetic system.

3. The Hybrid LINAC of claim 1, wherein the traveling wave linear accelerator section (TW accelerator) is cooperative with a second external magnetic system.

4. The Hybrid LINAC of claim 1, wherein the first RF Transmitting Waveguide includes a High Power Circulator so as to prevent reflected RF power from propagating back to the RF source.

5. The Hybrid LINAC of claim 1, wherein the second RF Transmitting Waveguide includes a Low Power Circulator so as to prevent reflected RF power from propagating back to the TW accelerator.

6. The Hybrid LINAC of claim 1, wherein broad energy regulation of the output beam of electrons provides energy regulation from 0.5 MeV to maximum LINAC energy.

7. The Hybrid LINAC of claim 1, further comprising at least one of: an electron beam window and a conversion target for producing Bremsstrahlung radiation.

8. A Hybrid LINAC with high beam efficiency and broad energy regulation for security inspection, non-destructive testing, radiotherapy, and electron beam irradiation of objects, the Hybrid LINAC comprising: an electron gun configured to provide an input beam of electrons; a standing wave linear accelerator section (SW Buncher) configured to receive the input beam of electrons and accelerate the electrons, the SW Buncher including an SW Input RF Coupler, the SW Buncher providing an intermediate beam of accelerated electrons; a traveling wave linear accelerator section (TW accelerator) configured to receive the intermediate beam of accelerated electrons, and to further increase the momentum and energy of the accelerated electrons, the TW accelerator including a TW Input RF Coupler and a TW Output RF Coupler, the TW accelerator providing an output beam of electrons; a drift space configured to provide RF decoupling between the SW buncher and the TW accelerator, while also permitting transit of the intermediate beam of accelerated electrons from the SW buncher to the TW accelerator; an RF Splitter configured to receive RF energy, and to bifurcate the RF energy; an RF source configured to provide RF energy to the RF splitter via a first RF Transmitting Waveguide, the RF Splitter providing a first portion of the bifurcated RF energy to the SW Buncher via a second RF Transmitting Waveguide and the SW Input RF Coupler, the second RF Transmitting Waveguide also enabling the SW Buncher to be fed with RF power not used by the TW Accelerator so as to provide high beam efficiency of the output beam of electrons; and at least one of a Switch, a Phase Shifter, and a Power Adjuster, cooperative with both the the RF Splitter and the TW Input RF Coupler via a third RF Transmitting Waveguide, the at least one of a Switch, a Phase Shifter, and a Power Adjuster being capable of redistributing RF power between the SW Buncher and the TW Acellerator, and/or changing phase relationship between the SW Buncher and the TW Acellerator, thereby allowing the TW Accelerator to serve as an adjustable resonant load so as to provide broad energy regulation of the output beam of electrons.

9. The Hybrid LINAC of claim 8, wherein the standing wave linear accelerator section (SW Buncher) is cooperative with a first external magnetic system.

10. The Hybrid LINAC of claim 8, wherein the traveling wave linear accelerator section (TW accelerator) is cooperative with a second external magnetic system.

11. The Hybrid LINAC of claim 8, wherein the first RF Transmitting Waveguide includes a High Power Circulator so as to prevent reflected RF power from propagating back to the RF source.

12. The Hybrid LINAC of claim 8, further comprising: a Matched RF Load, cooperative with the TW Output RF Coupler, matched so as to absorb RF power remaining after acceleration in the TW Accelerator.

13. The Hybrid LINAC of claim 8, wherein broad energy regulation of the output beam of electrons provides energy regulation from 0.5 MeV to maximum LINAC energy.

14. The Hybrid LINAC of claim 8, further comprising at least one of: an electron beam window and a conversion target for producing Bremsstrahlung radiation.

15. A Hybrid LINAC with high beam efficiency and broad energy regulation for security inspection, non-destructive testing, radiotherapy, and electron beam irradiation of objects, the Hybrid LINAC comprising: an electron gun configured to provide an input beam of electrons; a standing wave linear accelerator section (SW Buncher) configured to receive the input beam of electrons and accelerate the electrons, the SW Buncher providing an intermediate beam of accelerated electrons; a traveling wave linear accelerator section (TW accelerator) configured to receive the intermediate beam of accelerated electrons, and to further increase the momentum and energy of the accelerated electrons, the TW accelerator including a TW Output RF Coupler, the TW accelerator providing an output beam of electrons; a Hybrid RF Coupler configured to provide RF coupling between the SW buncher and the TW accelerator, while also permitting transit of the intermediate beam of accelerated electrons from the SW buncher to the TW accelerator; an RF source configured to provide RF energy to both the SW Buncher and the TW accelerator via an RF Transmitting Waveguide cooperative with the Hybrid RF Coupler; and a Matched RF Load cooperative with at least one of a Switch, a Phase Shifter, and a Power Adjuster, the Matched RF Load also being cooperative with the TW Output RF Coupler, the Matched RF Load being matched so as to absorb RF power remaining after acceleration in the TW Accelerator in accordance with the at least one of the Switch, the Phase Shifter, and the Power Adjuster, thereby allowing the TW Acellerator to serve as an adjustable resonant load so as to provide broad energy regulation of the output beam of electrons, and so as to provide high beam efficiency of the output beam of electrons.

16. The Hybrid LINAC of claim 15, wherein the standing wave linear accelerator section (SW Buncher) is cooperative with a first external magnetic system.

17. The Hybrid LINAC of claim 15, wherein the traveling wave linear accelerator section (TW accelerator) is cooperative with a second external magnetic system.

18. The Hybrid LINAC of claim 15, wherein the first RF Transmitting Waveguide includes a High Power Circulator so as to prevent reflected RF power from propagating back to the RF source.

19. The Hybrid LINAC of claim 15, wherein broad energy regulation of the output beam of electrons provides energy regulation from 0.5 MeV to maximum LINAC energy.

20. The Hybrid LINAC of claim 15, further comprising at least one of: an electron beam window and a conversion target for producing Bremsstrahlung radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] For a fuller understanding of the invention, reference is made to the following Detailed Description, taken in conjunction with the accompanying drawings, in which:

[0050] FIG. 1 is a schematic diagram of a traditional SW linear accelerator (LINAC).

[0051] FIG. 2 is a graph of Electron Beam Energy vs. Peak Electron Beam Current showing changes to the LINAC load line (squares), in comparison with a corrected version based on Parmela simulations of beam dynamic (diamonds), and corresponding dose rate plots (X's and triangles, respectively) in a non-adapted standard single section LINAC, such as reduction of electron beam current and produced dose rate (if X-ray target is installed to produce bremsstrahlung) in a broad energy range due to effects of electron beam dynamics affected by changes in the accelerating RF field distribution in this energy range.

[0052] FIG. 3 is a schematic diagram of an embodiment of the hybrid LINAC of the invention, where an RF power circuit (which includes all elements (1, 2, 3, 18, 14, 19, 5) from RF source (1) to SW Buncher (5)) is configured in series with a “reversed” sequence (6, 18, 14, 19, 5), starting from the TW accelerating section (6) and continuing ultimately into the SW Buncher portion (5), the SW Buncher (5) serving as a final dissipating resonant RF load utilizing RF power productively for formation of the electron beam (10) in the SW buncher.

[0053] FIG. 4 is a schematic diagram of another embodiment of the hybrid LINAC of the invention with broad energy regulation, this embodiment having a variable RF Splitter (20) cooperative with a parallel RF feed (##) that includes at least one of: a switch, a phase shifter, and a power adjuster (15).

[0054] FIG. 5 is a schematic diagram of another embodiment of the hybrid LINAC of the invention having a single input RF coupler (4) and a matched RF load (9) cooperative with the TW Output Coupler (7) via an optional RF Switch (8).

DETAILED DESCRIPTION

[0055] In an embodiment of the present invention shown in FIG. 3, RF power from the RF Power Source (1) propagates through an RF Transmitting Waveguide (2) via an optional High Power Circulator (3) (used at the RF power source, where propagating power is at its highest value) into the TW Input RF Coupler (18) of the TW Linear Accelerator Section (6). The TW Linear Accelerator Section (6) is RF-decoupled from a Standing Wave Buncher (5) by a Drift Space (14). While the RF Power Source (1) can run RF power into the TW Input RF Coupler (18) without an isolating device in steady state mode, a High Power Circulator (3), installed between the RF Power Source (1) and the TW Input RF Coupler (18), is desirable.

[0056] The RF Couplers (19, 18, 7) are configured to match impedance of the external and internal RF circuit so as to minimize power reflections at the operating RF frequency while running at nominal energy and beam current values. The High Power Circulator (3) prevents reflected power from propagating back to the RF source (1). Therefore, most or all of the RF power from the RF Power Source (1) enters the TW Input RF Coupler (18), propagates within the TW LINAC Section (6), thereby forming an accelerating TW field distribution, and is also transferred to the electron beam. The remaining power, which exits through TW Output RF Coupler (7) is transmitted into the SW Buncher (5) through the RF Transmitting Waveguide (2), connecting Switch and/or Phase Shifter and/or Power adjuster (16) and optional Low Power Circulator (17) (installed after the propagating power has become much lower than right after the magnetron due to some reflections, attenuation in the TW LINAC, and power consumed by the electron beam), then entering the SW Buncher (5) through the SW Input RF coupler (19).

[0057] Thus, the Hybrid LINAC of the invention is divided into two parts—the Standing Wave (SW) Buncher (5) and the Traveling Wave (TW) Accelerating Section (6), with Reverse Feeding Sequence (RFS) via the RF Transmitting Waveguide (2), Switch and/or Phase Shifter, and/or Power Adjuster (16) and the optional Low Power Circulator (17), such that the SW Buncher (5) is fed with RF power remaining after attenuation and e-beam acceleration in the TW section (6), thereby increasing the efficiency of the LINAC.

[0058] The Magnetic System (13), such as an external focusing solenoid or a permanent periodic magnet (PPM) system, is optional. The Magnet System (13) is preferably omitted, because including it increases complexity, power consumption, and consequently increases the cost of the LINAC system. Simulations of several specific examples demonstrated that use of an external focusing system (13) will improve current transmission by only 20% or similar percentage, while adequate characteristics of electron beam can be achieved without the use of such a system (13).

[0059] Electron beam energy and other output characteristics are regulated by means of changing phase and/or power by the Switch and/or Phase Shifter and/or Power Adjuster (16) installed in the RF Transmitting Waveguide (2) between the TW Output RF Coupler (7) and the SW Output RF Coupler (19), which may include at least one of: a switch, a fast and/or slow phase shifter, and a power regulator (16). Use of a Power Adjuster may be combined with regulation of beam current and/or input power so as to optimize the ouput RB characteristics. The electron beam current and the RF power can be optimally adjusted for each desired set of operating parameters. Along the RF Transmitting Waveguide (2), after the Switch and/or Phase Shifter and/or Power Adjuster (16) there may be an optional Low Power Circulator (17) installed, which is not critical to system operation, but may improve its performance, in certain aspects.

[0060] This combination of the SW and TW sections exploits several advantages of both. For example, the main operational frequency of the LINAC is largely defined by the SW buncher (5), while the TW section (6) is more broadband and is easily tuned to the required resonance frequency of the SW buncher (5). Therefore, the Automatic Frequency Control (AFC) is based on the SW buncher section (5), which is common for the SW LINACS, and it is a straightforward, proven configuration, while if it is only based on the TW section, the AFC is much more complex so as to ensure steady operation of the LINAC. The SW buncher section (5) permits effective RF focusing of the electron beam while reaching the relativistic speed, and further acceleration in the TW section (6) can also be done without any external magnetic system, as we described earlier.

[0061] Exploring a design example at 9300 MHz, using a PM-1110X X-band magnetron manufactured by L-3, the design parameters for a 60 cm long hybrid RF structure have shown to be superior to the existing non-hybrid configurations with similar characteristics, delivering a steady beam at energy in broad energy range of 1 MeV to 7 MeV, with a maximum output dose rate of 1100 R/min at 1 m, which corresponds to over 1700 R/min @ 80 cm, while delivering a substantial dose rate at low energy, estimated in tens of R/min at 1 m. Such a compact LINAC system with record high radiation beam characteristics can find its applications useful in many fields, such as Non-Destructive Testing (NDT), Security Screening (SI), Radiation Therapy (RT), etc.

[0062] Referring to FIG. 4, in another embodiment of the invention, the hybrid LINAC structure includes a parallel feed. In this configuration, the RF Source (1) provides RF power through an RF Transmitting Waveguide (2), via a High Power Circulator (3), which is then split by the RF splitter (20). A portion of the RF power determined by the dividing ratio of the RF Splitter (20) is forwarded to the SW Output RF Coupler (19), and the remaining power is forwarded through the second arm of the RF Splitter (20) to the TW Input RF Coupler (18) through the Switch/Phase-shifter (16) similar to that used in the preferred embodiment described in FIG. 3.

[0063] In the embodiment of FIG. 4, RF power remaining after acceleration in Traveling Wave Linear Accelerator Section (6) is forwarded to and absorbed by the matched RF load (9). The embodiment of FIG. 4 is not as efficient as the embodiment of FIG. 3. For example, using the similar PM-1100X magnetron based design example, the LINAC output dose rate of the embodiment of FIG. 4 will be approximately 10% less than in the case of the embodiment of FIG. 3, while maintaining the other qualities of the embodiment of FIG. 3.

[0064] With reference to FIG. 5, in another embodiment of the present invention, a Hybrid Input RF Coupler (4) serves as a combined single RF power input for both the SW and TW sections. The radiation beam parameter RF Switch (8) can be installed at the RF output of the TW section, right after the TW Output RF Coupler (7), and before the matched RF Load (9).

[0065] Other modifications and implementations will occur to those skilled in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the above description is not intended to limit the invention, except as indicated in the following claims.