Efficient distributed coupled linear accelerator design

Abstract

A linear accelerator having a plurality of cavities along a beam line supplied with power by a pair of distribution waveguide manifolds having a sequence of feed arms connecting the manifolds to unit portions and a single RF (Radio Frequency) feed is described herein. The distribution waveguide manifolds are connected to the unit portions such that alternating pairs of unit portions are connected to opposing distribution waveguide manifolds. Each cavity is individually optimized according to the electron velocity along the beam line. The geometry of the unit joints and connection channels between the manifolds and cavities may be individually optimized along beam lines, and may include serpentine configurations to provide consistent RF channel lengths between the manifolds and different cavities. Methods of designing linear accelerators and manufacturing accelerators are also provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This PCT application claims the benefit of priority to U.S. Provisional Application No. 63 / 344,322, filed on May 20, 2022, which is incorporated herein by reference in its entirety. STATEMENT AS TO RIGHTS TO INVENTS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0002] This invention was made with government support under DE-SC0017771 awarded by the U.S. Department of Energy. The government has certain rights in this invention. Technical Field

[0003] The present invention relates generally to linear accelerator design and associated features, systems and methods of use, design and manufacture. Background Art

[0004] Conventional linear particle accelerators typically have low RF-to-beam efficiency, with only about 20%-30% of the RF power used for beam acceleration, while the rest of the power is deposited as heat in the copper structure. These conventional designs either aim to produce high gradients and involve cavities that are coupled to adjacent cavities via beam tunneling (see, e.g., (1) C. Karzmark, C. Nunan, and E. Tanabe, Medical Electron Accelerators. Chapter 3, ISBN: 97 071054102 (McGraw-Hill Companies, Health Professionals Division, 1993); (2) T. Wangler, Rf Linear Accelerators. Chapter 4 (Wiley, New York, 2008); (3) T. Maury and C. Wu, Handbook Of Accelerator Physics And Engineering, 3rd Edition (World Scientific, Singapore, 1999)), or avoid such coupling problems by using dual-period or side-coupled cavities, but cannot handle high gradients (see, e.g., (4) EAKnapp, Linear Accelerator Conference. Conference, MURA-714, p. 31. (1964); (5) E. A. Knapp, B. C. Knapp, and J. M. Potter, Standing wave high energy linear accelerator structures, Rev. Scient. Ins. 39, 979 (1968). In the first case, coupling of adjacent cells limits the ability to optimize the cavity shape. Side-coupled and dual-period linear accelerators are more amenable to cavity optimization but suffer from RF losses in these coupler cavities. These cavities are considered to be idle cavities with no energy stored in them, but this is a misconception because Poynting vector theory dictates that power must flow through these side cavities to provide power to the accelerating cavity, which is separated from the feed waveguide of the structure by many of these side-coupled cavities. The basic concept of distributed coupling solves some of these problems. Distributed coupling allows each accelerator cell to be fed independently using a periodic feed RF network.(See, e.g., 1) U.S. Patent 9,386,682; (2) Sami Tantawi, Mamdouh Nasr, Li Zenghai, Cecile Limborg, and Philipp Borchard, “Design and demonstration of a distributed-coupling linear accelerator structure,” Phys. Rev. Accel. Beams 23, 092001, September 10, 2020; (3) Peter G. Maxim, Sami G. Tantawi, and Billy W. Loo Jr., “PHASER: A platform for clinical translation of FLASH cancer radiotherapy,” Radiotherapy and Oncology 139, October 2019. However, this approach presents challenges that, so far, have imposed practical limits on the scale and efficiency of such accelerators.

[0005] Therefore, there is a need for an improved LINAC design that has improved efficiency and is relatively compact. There is a further need for such a LINAC design that has simplified power source requirements. There is an additional need for such a LINAC design that can be optimized for a wide range of capabilities in a practical manner in terms of design and manufacturing. Summary of the invention

[0006] The present invention relates to a highly efficient distributed coupling linear accelerator, in particular to a linear accelerator having a plurality of cavities which are distributedly coupled to a pair of RF waveguide manifolds.

[0007] In one aspect, the invention relates to a linear accelerator comprising a Y-coupler RF waveguide in combination with a vacuum port and an RF window.

[0008] In some embodiments, the linear accelerator includes a single RF feed shared by two manifolds. The single RF feed may include a Y-coupler RF waveguide that distributes the RF input along its middle portion to each of a pair of manifolds, which in turn feeds each cavity through distributed coupling. In some embodiments, a plurality of cavities include a buncher and a capture cavity portion and an acceleration portion with an acceleration cavity, and the single RF feed is common to the entire accelerator structure. In some embodiments, by iteratively applying the scattering matrix to the design of each cavity, each cavity in the cavity of the entire structure is optimized. In some embodiments, the accelerator design is such that the accelerator body includes all cavities, manifolds, and joint couplers, and can be made by a CNC machine. Similarly, the RF power supply assembly may include a Y-coupler made by a CNC machine and having minimal parts.

[0009] In one aspect, the present invention relates to a linear accelerator comprising: a body defining: a plurality of cavities along a beam line extending between an input and an output; a pair of distribution waveguide manifolds; a sequence of feed arms connecting the manifolds to the plurality of cavities; wherein the distribution waveguide manifolds are connected so that alternating pairs of unit sections are connected to opposing distribution waveguide manifolds; and a single RF power feed common to both the pair of distribution waveguide manifolds and the plurality of cavities. In some embodiments, the single RF power feed comprises a Y-coupler RF waveguide. In some embodiments, the Y-coupler RF waveguide comprises a body divided into two arms, each of the two arms extending to an RF port of a corresponding manifold of a pair of waveguide manifolds. In some embodiments, the Y-coupler RF waveguide comprises an RF window for a single RF input. Optionally, the Y-coupler is designed to be machinable on a CNC machine. In some embodiments, each of the plurality of cavities is optimized. In some embodiments, the design of each of the plurality of cavities is individually optimized by application of a scattering matrix.

[0010] In some embodiments, each of the plurality of cavities is individually optimized by adjusting their length and shape for electron velocity at the location of the corresponding cavity along the beam line. In some embodiments, the plurality of cavities includes one or more cavities defined for the buncher and capture sections such that the length is optimized to match the beam arrival time to the RF phase for varying sub-velocities of the beam velocity along these sections. In some embodiments, the buncher and capture sections include at least one cavity configured for both the buncher and capture functions with varying lengths (periods) to accommodate slowly varying beam velocities as they approach the speed of light.

[0011] In some embodiments, the plurality of cavities comprises a plurality of subsequent cavities along a beamline defined as an acceleration section. In some embodiments, a common RF feed provides power to both the buncher and the capture section and the acceleration section. In some embodiments, a sequence of feed arms is defined as a plurality of T-cell joints. In some embodiments, the geometry of each of the plurality of T-cell joints coupling the manifold to the plurality of cells is optimized such that its dimensions vary along the length of the beamline to appropriately provide power of the correct phase to each cavity. In some embodiments, the geometry of each of the plurality of T-cells coupling the manifold to the plurality of cells is designed to be machinable on a CNC machine. In some embodiments, each waveguide manifold comprises a plurality of apertures and mitered elbows to allow for uniform distribution of power in the forward direction with minimal losses.

[0012] In another aspect, the present invention relates to a method for designing an efficient distributed linear accelerator. This method may include: determining the geometry of a linear accelerator body to be defined by a conductive metal block, the body having a plurality of cavities aligned along a central beam line and a pair of manifold waveguides on opposite sides of the central beam line, the pair of manifold waveguides being used to distribute power to the plurality of cavities from a single common RF feed; and determining the geometry of a plurality of waveguide coupling joints between the pair of manifolds and each of the cavities to transmit RF from the pair of manifolds to the plurality of cavities. In some embodiments, the corresponding cavities are individually optimized by applying a scattering matrix, and this same optimization method is iteratively applied to each of the other cavities in the plurality of cavities, so that the geometry of each of the plurality of cavities is optimized for the electron velocity associated with a given position along the beam line.

[0013] In some embodiments, due to different geometries of the plurality of cavities, the distances between the plurality of cavities and the respective manifolds coupled thereto vary along the beam line. In such embodiments, the method may further include determining the geometry of the plurality of waveguide coupling joints to include a serpentine portion such that the length of the waveguide channel of each of the plurality of waveguide coupling joints is consistent along the beam line. In some embodiments, the method may further include determining the geometry of a Y-coupler RF waveguide for a single RF feed to supply RF power to both the manifold and the plurality of channels throughout the linear accelerator.

[0014] In yet another aspect, the present invention relates to a method of making a highly efficient distributed linear accelerator. Such a method may include: manufacturing a linear accelerator body from a conductive metal such as copper, the body having a plurality of cavities aligned along a central beam line and a pair of manifolds on opposite sides of the central beam line, the pair of manifolds being used to distribute power supply to the plurality of cavities, wherein the linear accelerator body is defined by an upper half and a lower half; manufacturing a plurality of waveguide coupling joints between the pair of manifolds and each of the cavities to transfer supply RF power from a single common RF power feed coupled to the pair of manifolds to the plurality of cavities, wherein each of the cavities is individually optimized by applying a scattering matrix so that the geometry of each of the cavities is optimized for an electron velocity associated with a given position along the beam line; and manufacturing a Y-coupler RF waveguide for coupling a single RF power feed to the pair of manifolds.

[0015] In some embodiments, one or both of the following: multiple cavities, a pair of manifolds, and multiple RF waveguide coupling joints are manufactured by a 3-axis CNC machine in two conductive metal blocks defining an upper half and a lower half; and a Y-coupler RF supply is formed by a 3-axis CNC machine, optionally in three or fewer parts.

[0016] In some embodiments, the linear accelerator is configured such that the connection between the T-junction and the cavity is achieved through a narrow, folded waveguide section of very specific length, which achieves any or all of the following goals: (1) preventing choking conditions on the T-junction when the cavity is tuned to non-resonance due to manufacturing errors or fault events; (2) the length of the folded waveguide provides a constant phase from the manifold to the cavity; and (3) using the folding of the waveguide as an additional degree of freedom to keep the total length between the manifold and the cavity independent of the position of the manifold exit to the cavity entrance; these distances between the manifold exit and the cavity entrance vary due to changes in the period of the cavity and the period of the T-junction.

[0017] In some embodiments, the first cavity of the linear accelerator can be fed independently with much lower power and varying phase to bunch the initial beam and thus affect the electrons captured from the DC gun. This is achieved by a separate waveguide coupling located on the top of the linear accelerator with separate feeding. In some embodiments, the feeding of the first cavity can be done by a tap from one of the manifolds so that it also couples power to the top of the linear accelerator from the outside, and the connection between this tap and the cavity can be done by a variable phase shifter and a variable attenuator in order to adjust the power to the first cavity. In some embodiments, power can also be supplied to the first cavity from a separate lock-in amplifier or oscillator. In some embodiments, power can also be supplied to the first cavity by tapping from the main power to the linear accelerator.

[0018] In some embodiments, not only can power be independently supplied to the first cavity as described above, but power can also be independently supplied to a group of initial cavities so that capture is not affected by the main power supplied to the linear accelerator. In some embodiments, the topology of such a linear accelerator described will allow the main power of the linear accelerator to be changed to produce a variable energy linear accelerator. In some embodiments, the initial cavity group can be supplied with power by their own Y-coupler and two manifolds as a sub-linear accelerator part of the main linear accelerator, thereby allowing capture to be changed by changes in power and phase between the first cavity and the remaining initial cavity group in addition to the change in energy in the embodiments described above, thereby allowing variable current. In some embodiments, by changing the phase and amplitude of the first cavity, the current to the main linear accelerator can generally be modified using only the bunching cavity used for variable dose linear accelerators.

[0019] It will be appreciated that the innovations described herein enable large-scale production of distributed linear accelerators with high yields, which have advantages in terms of compactness, weight and required RF power, and further allow them to be easily designed and manufactured. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A linear accelerator design according to some embodiments is shown.

[0021] Figure 2A and Figure 2B Shows Figure 1 A cross-sectional view of the accelerator design in Figure 1.

[0022] Figure 3 Shown is a detailed view of a common RF feed input assembly that may be attached to the middle portion of the linear accelerator body to provide RF power to the pair of manifolds, according to some embodiments.

[0023] Figure 4 A detailed view of a Y-coupler of an RF feed assembly is shown in accordance with some embodiments.

[0024] Figure 5A-5D Different cavity designs are shown for exemplary linear accelerator designs in accordance with some embodiments.

[0025] Figure 6 Shown is a side view of an RF waveguide manifold having multiple T-junction couplers feeding adjacent cavities of a beamline according to some embodiments.

[0026] Figure 7A T-junction coupler between a manifold and a cavity is shown, the T-junction including a serpentine portion, according to some embodiments.

[0027] Figure 8 An electric field model of an exemplary linear accelerator design is shown in accordance with some embodiments. DETAILED DESCRIPTION

[0028] The present invention relates to a highly efficient distributed coupling linear accelerator, in particular a linear accelerator having multiple cavities that are distributed coupled to a pair of manifolds. The topology of this distributed coupling allows the coupling between units to have a wide range of acceptable values, including being negligibly coupled. The accelerator cells can then be optimized individually to achieve the highest shunt impedance and / or to provide high field gradients by adjusting the fields on the cell walls (see, for example, 1) U.S. Patent 9,386,682; (2) Sami Tantawi, Mamdouh Nasr, Li Zenghai, Cecile Limborg, and Philipp Borchard, “Design and demonstration of a distributed-coupling linear accelerator structure,” Phys. Rev. Accel. Beams 23, 092001, September 10, 2020; (3) Peter G. Maxim, Sami G. Tantawi, Billy W. Loo Jr., “PHASER: A platform for clinical translation of FLASH cancer radiotherapy,” Radiotherapy and Oncology 139, October 2019. To date, the designs adopted for distributed coupled linear accelerators use π phase shifts between adjacent cavities to achieve maximum isolation between cavities. This allows the RF to be fed through two sets of manifolds. In this example, the manifold can be further simplified by providing power from the manifold to one cavity every λg / 2, resulting in the dual-cavity alternating tap design shown. Existing designs for conventional linear accelerators have a dedicated buncher section with its own RF feed, and a speed of light (SOL) section with the same cavity and a manifold for providing RF power to these cavities. In this example, the buncher and the accelerating cavity can be unified into a compact and efficient structure with a common RF feed. This approach is very desirable for producing such a linear accelerator, especially if it is a stand-alone device starting with a low-pressure gun. However, the proposed concept of distributed coupling may bring certain design challenges, which can be solved by utilizing various novel layout methods and design features, as discussed in further detail below. I. Linear Accelerator Structure

[0029] Figure 1An exemplary linear accelerator design 100 utilizing the concepts described above is shown. Figure 2A and Figure 2B Shows Figure 1 Cross-sectional view of the linear accelerator design in Figure 2. Figure 2A A vertical cross section 101 along beam line B is shown, and Figure 2B A horizontal cross section 102 along beam line B is shown. This design includes a body consisting of an upper half and a lower half, which define dual waveguide manifolds 10a, 10b disposed on opposite sides of a central beam line 10c. An electron gun 21 (e.g., eGun) is disposed at the proximal end of the body 10, an input monitor 20 can be coupled to the buncher cavity 10c-1, and an RF power supply assembly 30 is attached to the middle portion of the body 10 within the acceleration section having the acceleration cavity 10c-2 and feeds the corresponding RF power ports in each manifold (see RF port 11b of manifold 10b in FIG. 2 ). A beam monitor 40 is disposed at the top of the beam monitoring cavity 10c-3 before the beam exits the beam outlet 50 at the distal end of the body 10. In one noteworthy aspect, the linear accelerator body combines the buncher portion and the rest of the linear accelerator in one structure (no need for a separate buncher portion with a separate power supply), which is advantageous in many respects compared to conventional distributed coupled linear accelerators. As can be seen from Figure 2B As seen in Figure 1, the body 10 includes a T-junction coupler that provides an RF path between the manifold and the cavity 10c. In this design, the cavities are coupled to adjacent manifolds in pairs. Since the various portions of the manifold between the couplers 11 and the various cavities 10c are optimized, the geometry of each is different along the beam line, complicating the geometry of the coupler 11. The serpentine section 13 is included to provide a consistent RF path length between the manifold and the cavity, allowing a single RF source to power the entire structure.

[0030] Figure 3 A single RF supply assembly 30 is shown that brings power from the RF source to the Figure 1 Two manifolds in a linear accelerator. Figure 4A detailed view of the Y-coupler 31 of the RF assembly is shown. The RF window 35 at the top of the RF supply assembly 30 allows RF power to be transmitted therethrough, thereby providing power to the linear accelerator manifold. The Y-coupler 31 can be formed as one or more components. The Y-coupler includes a body and two distal arms 31a, 31b, which extend to corresponding RF ports of each of a pair of manifolds 10a, 10b, and may include interface features 32a, 32b and 33, 34. In some embodiments, the Y-coupler 31 is designed to be machined on a 3-axis CNC machine and has a minimum number of parts (e.g., less than three or fewer parts, two parts, a single integral component).

[0031] For a distributed coupled linear accelerator, the structure including the RF distribution manifold and the cascaded T-junctions is designed so that the power in the feed line has the least effect on the cavity cells. This can be achieved when the RF wave reaches a minimum standing wave ratio (SWR) in the feed line of the cavity. In addition, in this π-mode operation, the cavities are independent of each other. This results in two almost isolated systems: the RF feed network and the individual cavities, allowing them to be optimized independently. Advantageously, a unit-by-unit optimization can be performed to extend this topology to the bunching and capture section, during which the velocity of the electrons changes very quickly. In one aspect, the cavity size and its position along the beam path and the choice of manifold and meandering feed line sizes are optimized to obtain maximum RF to beam efficiency. In some embodiments, this approach allows the accelerator to perform optimal capture without focusing magnets and with minimal sensitivity to dimensional tolerances. In some embodiments, the beam tunnel, especially in the initial section, is optimized and modified to maximize the capture of electrons. II. Design 1. Cavity optimization

[0032] In one aspect, the linear accelerator design of this article modifies the existing distributed coupling-based linear accelerator (linac) topology and design method. This modified method allows the optimization of unit shapes (e.g., high shunt impedance) for efficiency and improves gradient handling capabilities. For a 10MeV, 300mA linear accelerator, the design utilizes a genetic optimization algorithm that can produce the highest possible gradient. In this embodiment, it is configured to produce a cavity shape with a shunt impedance of about 180MΩ / m. In another aspect, the design makes it easy to process. For example, when assembling a linear accelerator from these cavities, the minimum practical wall thickness is maintained between the structures to maintain mechanical integrity during processing, and the design of the concave features complies with the processing rules of a conventional 3-axis milling machine. In some embodiments, the first buncher cavity is additionally designed and simulated in conjunction with the electron gun, and its position is optimized to achieve maximum electron capture.

[0033] Figure 5A-5D Different cavity designs generated by the algorithm are shown. Figure 5A Shown are the first buncher cavity (green, on the right) and the electron gun, where the first buncher cavity is located at an optimal distance from the electron gun to maximize electron capture. Figure 5B-5D The electric field in examples of different cavity shapes is shown. Each of these cavities is individually optimized for a different electron velocity along the beam line. As the electrons are accelerated and their average velocity increases, a different cavity type optimized for that velocity is used until the velocity reaches approximately the speed of light. The linear accelerator then continues to use only one cavity type, Figure 5B The lightspeed cavity shown. This judicious combination of different cavity shapes along the length of the linear accelerator allows for a unified bunching and acceleration section with a common RF feed, a unique feature that clearly deviates from conventional designs. 2. Manifold design

[0034] In another aspect, the optimal cavity type and location are selected through an iterative process to maximize electron capture along the length of the linear accelerator. In particular, it is desirable to maintain the π-mode characteristics of the structure while allowing the cavity fields to synchronize with the electron beam despite their rapid changes. In order to keep the phase advance between the cavities constant, the distance between the cavities must be changed from a smaller value to a larger value as the speed of the electrons increases to reach the speed of light. The distance between the cavities can then be maintained at half the free space wavelength. As described above, the cavities have been optimized with different lengths to allow for this design approach. Therefore, in such embodiments, the RF feed network must have a varying distance between the tap points to follow the cavity position. This can be achieved by varying the size of the manifold feed network to change the guide wavelength along the manifold, so that the distance between the taps is maintained at half the guide wavelength, while the physical distance is varied to adapt to the cavity position. Therefore, the sections between the tap points are also optimized along the beam line.

[0035] Optimal design of manifold junctions requires achieving minimal standing waves within the manifold waveguide. To achieve this, each three-port network representing the manifold with the feed point must have an accurate scattering matrix representation. This mathematical representation can be achieved by adding features at the junctions so that the manifold exerts minimal influence on the cavity. This allows the cavity coupling to be tuned individually.

[0036] In another aspect, the exemplary system is designed to have a single RF feed for the entire system, including the capture and bunching sections. This is a considerable improvement over conventional designs that require multiple separate power feeds for the different sections. In this embodiment, each RF manifold block connected to each linear accelerator cavity has been optimized individually. The RF manifold block includes a T-shaped unit / junction 11 and a waveguide section 10b extending between the junctions, such as Figure 6 As shown. Since each T-cell junction has a different size, the guided wavelength is adjusted according to the position, ensuring a smooth transition between one T-cell junction and its neighbors to prevent sharp steps along the manifold that would otherwise cause RF reflections and manufacturing difficulties. The depth and height of each T-cell can be adjusted individually on either side of the T-junction coupler 11, and a cutout 12 or aperture feature is included at the junction of the 3-port structure to compensate.

[0037] Figure 6-Figure 7 A series of such T-junctions are shown. Figure 6 A portion of an RF manifold 10b is shown, showing an RF manifold block including a single T-unit connector 11 that is seamlessly connected together. Each T-unit connector 11 extending from the RF manifold feeds an adjacent cavity of the beam line to which it is connected. In some embodiments, the manifold block opposite the T-unit connector includes an inwardly curved portion 12 to prevent RF reflections. In addition, the manifold and T-unit connectors can include various design features to optimize RF transmission and avoid reflections, such as avoiding any sharp corners (e.g., by utilizing rounded corners). As described above, due to changes in the cavity geometry of the optimized cavity, the distance from the manifold must change, so in order to maintain a consistent distance for the RF path between the manifold and the cavity, the T-unit connector can include a non-linear channel of any suitable geometry, such as a serpentine channel. Figure 7 A half cross section of the accelerating chamber 10c-2 along the beam line connected to the manifold T-unit junction 11 using an optimized meandering section 13 is shown.

[0038] In some embodiments, the entire manifold is constructed using this design approach. In addition, a Y-coupler can be added in the center of the manifold so that the linear accelerator is fed by a single input waveguide. Figure 8The electric field model of this design is shown in (the beamline cavity is not shown). The electric field values ​​in the color map are identified as red (r), orange (o), yellow (y), green (g), blue (b), and indigo (i). Indicated as In one aspect, the geometry of each RF section between adjacent T-coupled joints is optimized so that the size of each RF section varies along the length of the beamline. In some embodiments, this linear accelerator design includes judicious selection of apertures and mitered elbows to allow uniform distribution of power with minimal loss in the forward direction. The resulting S matrix for the manifold structure is shown in Table 1. It is noteworthy that despite the lack of uniformity in the distance between the taps, the scattering matrix indicates a very uniform power distribution while maintaining the correct π phase advance. In addition, in this approach, the reflection S11 is minimal. It should be understood that the scattering matrix in U.S. Patent 9,386,682 or variations thereof can be utilized to design a linear accelerator, for example by iterative application to each cavity so as to optimize each cavity for a given electron velocity along the beamline. For example, the optimal design of the manifold joint should achieve the minimum standing wave in the manifold waveguide. To this end, each three-port network representing the manifold with a feed point can be fitted with the following scattering matrix: Where n is the number of cavities fed by a single manifold. This will ensure that a minimum VSWR is obtained along the manifold. To achieve this matrix, the shape of the waveguide around the manifold can be modified by using one or more features. One feature may include a protrusion on the wall of the waveguide that is opposite the wall of the feed with a joint. Another feature may include widening the feed from a narrow section to a wide section. It should be understood that various other features can be implemented in a similar manner. This approach can be used to design and scale linear accelerators to accommodate any desired capabilities, such as designing linear accelerators from 1MeV to 1GeV and above.

[0039] Table 1: Scattering matrix 3. Beam dynamics

[0040] In yet another aspect, linear accelerator beam dynamics are simulated using full 3D particle tracking techniques, allowing simulation of nonlinear and space charge effects of charged particle dynamics in electromagnetic fields. As described in the cavity section, electromagnetic fields of several different cavity types are generated. An iterative method is used to select the cavity type and the distance between consecutive cavities. As the beam propagates along the length of the linear accelerator, particles are lost. The loss rate is high in the first few cavities and then becomes minimal. Nevertheless, this causes the beam load to vary from cavity to cavity. Therefore, the external coupling of the cavity needs to be adjusted. The appropriate coupling coefficient for each cavity can be calculated separately. Then, not only does the cavity type vary along the linear accelerator, but the geometry of the coupling hole also varies from cavity to cavity. This is an extremely tedious process, however, automating the process allows sufficiently fast design cycles to become feasible. 4. Linear Accelerator Integration

[0041] In yet another aspect, the preceding sections have described a process for designing and tuning the cavity and manifold tees for optimal beam propagation. Thus, methods have been developed to optimize the connection of the manifold tees to the cavity while maintaining the phase relationship and isolation between the two structures. In some embodiments, the shape of the connecting channel is selected to satisfy several conditions: (1) it must connect seamlessly with both the cavity and the tee openings; (2) the feature needs to be easily machined on a conventional CNC machine; and (3) it must have a minimal lateral width so that the linear accelerator is narrow and, therefore, compact and lightweight. In some embodiments, these conditions are met by using a serpentine structure, such as Figure 7 The length of the meander is optimized by splitting the structure in half along the middle of the U-shaped bend in the meander (see Figure 7 The two structures thus created: cavity + half-meander and T-junction plus half-meander section were analyzed for frequency and phase at the U-bend port. The sum of the phases of the RF beams arriving at this location from either side should be 90°. The length of the meander was then adjusted until a 90° phase was achieved. This ensured minimal loss of power transmitted down the manifold, as well as minimal coupling between adjacent cavities. 5. Beam tunnel design

[0042] In yet another aspect, particle acceptance and forward propagation require maximum capture of charged particles at each stage, especially in the bunching section. The size of the beam tunnel that allows the particles to travel forward needs to be optimized to minimize interaction with the walls and maximize interaction with the cavity field. Typically, a single tunnel diameter is used throughout the interaction length of the entire linear accelerator. It can be found that changing the diameter of the tunnels in various parts of the linear accelerator, especially in the buncher region, can significantly improve the efficiency of the linear accelerator. This feature is another fundamental departure from traditional linear accelerator design.

[0043] The methods, systems, and devices discussed above are examples. It should be understood that each of the above aspects can be incorporated into a linear accelerator design to impart certain advantages described herein, either alone or in combination with any other design features discussed herein. Various configurations may omit, replace, or add various procedures or components as appropriate. For example, in an optional configuration, the method may be performed in an order different from that described, and / or various stages may be added, omitted, and / or combined. In addition, the features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. And further, technology is constantly evolving, and some of the elements described are provided as non-limiting examples, and therefore do not limit the scope of the present disclosure or claims.

[0044] Specific details are given in the description to provide a thorough understanding of the exemplary configurations (including implementations). However, the configurations can be made without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary details to avoid obscuring the configurations. This description provides exemplary configurations that do not limit the scope, applicability, or configurations of the claims. Instead, the foregoing description of the configurations will provide those skilled in the art with an implementation description for implementing the described techniques.

[0045] In addition, the configuration can be described as a process or method. Although the various steps can be described as a continuous process, some operations can be performed in parallel or concurrently. In addition, examples of methods can be implemented by hardware, software, firmware, middleware, microcode, hardware description language, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments for performing the necessary tasks can be stored in a non-transient computer readable medium, such as a storage medium. The processor can perform any or all of the steps.

[0046] Having described several exemplary configurations, various modifications, alternative structures, and equivalents may be used without departing from the spirit of the present disclosure. The above elements may be components of a larger system, in which other rules may take precedence over or modify the application of the present invention. Therefore, the above description does not limit the scope of the claims. All patents, patent applications, and other publications cited in this application are incorporated by reference in their entirety for all purposes.

Claims

1. A linear accelerator, comprising: A subject, the subject defining: a plurality of cavities along a beam line extending between an input and an output; a pair of distribution waveguide manifolds; connecting the manifold to a sequence of feed arms of the plurality of cavities; wherein the distribution waveguide manifolds are connected such that alternating pairs of unit sections are connected to opposing distribution waveguide manifolds; and The pair of distribution waveguide manifolds and the plurality of cavities share a single RF power feed.

2. The linear accelerator according to claim 1, characterized in that The single RF power feed includes a Y-coupler RF waveguide.

3. The linear accelerator according to claim 1, characterized in that: The Y-coupler RF waveguide includes a body divided into two arms, each of the two arms extending to an RF port of a corresponding one of the pair of waveguide manifolds.

4. The linear accelerator according to claim 3, characterized in that: The Y-coupler RF waveguide includes an RF window for a single RF input.

5. The linear accelerator according to claim 3, characterized in that: The Y-coupler is designed to be machined on a CNC machine.

6. The linear accelerator according to claim 1, characterized in that: Each cavity of the plurality of cavities is optimized.

7. The linear accelerator according to claim 6, characterized in that: The design of each of the plurality of cavities is individually optimized by applying a scattering matrix.

8. The linear accelerator according to claim 6, characterized in that: Each of the plurality of cavities is individually optimized by adjusting their length and shape for electron velocity at the location of the corresponding cavity along the beam line.

9. The linear accelerator according to claim 1, characterized in that: The plurality of cavities includes one or more cavities defined for buncher and capture sections such that the lengths are optimized to match the beampack arrival times to the RF phase of the varying sub-velocities of the beam velocity along these sections.

10. The linear accelerator according to claim 9, characterized in that The buncher and trapping portion includes at least one cavity configured for both buncher and trapping functions with varying length or period to accommodate slowly varying beam velocities as they approach the speed of light.

11. The linear accelerator according to claim 9, characterized in that: The plurality of cavities includes a plurality of subsequent cavities along the beam line defined as an acceleration section.

12. The linear accelerator according to claim 11, characterized in that The common RF feed provides power to both the buncher and capture section and the acceleration section.

13. The linear accelerator according to claim 1, characterized in that: The series of feed arms is defined as a plurality of T-shaped unit junctions.

14. The linear accelerator according to claim 13, characterized in that: The geometry of each of the plurality of T-cell joints coupling the manifold to the plurality of cells is optimized such that the size of the T-cell joints varies along the length of the beamline to properly supply power of the correct phase to each respective cavity of the plurality of cavities.

15. The linear accelerator according to claim 13, characterized in that: The geometry of each of the plurality of T-shaped units coupling the manifold to the plurality of units is designed to be machined on a CNC machine.

16. The linear accelerator according to claim 1, characterized in that Each waveguide manifold includes multiple apertures and mitered elbows to allow for even distribution of power in the forward direction with minimal losses.

17. A method for designing an efficient distributed linear accelerator, the method comprising: determining the geometry of a linear accelerator body to be defined by a conductive metal block, the body having a plurality of cavities aligned along a central beam line and a pair of manifold waveguides on opposite sides of the central beam line for supplying power to the plurality of cavities from a single common RF feed; determining a geometry of a plurality of waveguide coupling junctions between the pair of manifolds and each of the cavities to transmit RF from the pair of manifolds to the plurality of cavities, wherein the respective cavities are individually optimized by applying a scattering matrix, and this same optimization method is iteratively applied to each of the other cavities in the plurality of cavities such that the geometry of each of the plurality of cavities is optimized for an electron velocity associated with a given position along the beam line.

18. The method according to claim 17, characterized in that Due to different geometric shapes of the plurality of cavities, distances between the plurality of cavities and respective manifolds coupled thereto vary along the beam line, the method further comprising: The plurality of waveguide coupling junctions are geometrically shaped to include a serpentine portion such that a length of a waveguide channel of each of the plurality of waveguide coupling junctions is consistent along the beam line.

19. The method according to claim 17, The geometry of the Y-coupler RF waveguide for the single RF feed is determined to supply RF power to both the manifold and the plurality of channels throughout the linear accelerator.

20. A method for manufacturing a high-efficiency distributed linear accelerator, the method comprising: fabricating a linear accelerator body from a conductive metal such as copper, the body having a plurality of cavities aligned along a central beam line and a pair of manifolds on opposite sides of the central beam line for supplying power to the plurality of cavities, wherein the linear accelerator body is defined by an upper half and a lower half; making a plurality of waveguide coupling junctions between the pair of manifolds and each of the cavities to deliver supply RF power to the plurality of cavities from a single common RF power feed coupled to the pair of manifolds, wherein each of the cavities is individually optimized by applying a scattering matrix such that the geometry of each of the cavities is optimized for an electron velocity associated with a given position along the beam line; and A Y-coupler RF waveguide is fabricated for coupling the single RF power feed to the pair of manifolds.

21. The method according to claim 20, characterized in that One or both of the following: The plurality of cavities, the pair of manifolds, and the plurality of RF waveguide coupling junctions are fabricated by a 3-axis CNC machine in two pieces of conductive metal defining the upper half and the lower half; and The Y-coupler RF supply is formed by a 3-axis CNC machine, optionally in three or fewer parts.

22. The linear accelerator according to claim 13, characterized in that The connection between the T-junction and the cavity is achieved through a narrow, folded waveguide section having a specific or optimized length, which achieves any or all of the following objectives: (1) preventing a choke condition on the T-junction when the cavity is tuned to non-resonance due to manufacturing errors or fault events; (2) the length of the folded waveguide provides a constant phase from the manifold to the corresponding cavity; (3) the use of the folding of the waveguide provides an additional degree of freedom to maintain the total length between the manifold and the cavity independent of the position of the outlet of the manifold to the entrance of the corresponding cavity, wherein the distance between the outlet of the manifold and the entrance of the corresponding cavity varies due to changes in the period of the cavity and the period of the T-junction.

23. The linear accelerator according to claim 1, characterized in that The linear accelerator is configured so that a first cavity of the multiple cavities can be independently fed with much lower power and varying phase in order to bunch the initial beam and thereby influence the trapped electrons from the DC gun, optionally this can be achieved by coupling a separate waveguide at the top of the linear accelerator with a separate feed.

24. The linear accelerator of claim 23, further comprising a tap from one of the manifolds to couple the power externally to the top of the linear accelerator, and the connection between the tap and the corresponding cavity is enabled by a variable phase shifter and a variable attenuator to adjust the power to the first cavity.

25. The linear accelerator according to claim 23, characterized in that The linear accelerator is configured such that power can also be supplied to the first cavity from a separate lock-in amplifier or oscillator.

26. The linear accelerator according to claim 23, characterized in that The linear accelerator is configured such that power can also be supplied to the first cavity by tapping from the main power to the linear accelerator.

27. The linear accelerator according to claim 23, characterized in that The linear accelerator is configured such that the first cavity can be independently powered, and optionally an initial set of cavities can be independently powered, such that the capture is not affected by the main power supplied to the linear accelerator.

28. The linear accelerator according to claim 27, characterized in that The configuration allows the main power of the linear accelerator to be varied so as to provide a variable energy linear accelerator.

29. The linear accelerator according to claim 27, characterized in that The linear accelerator is configured so that the initial set of cavities can be supplied with power by their own Y-couplers and two manifolds as sub-sections of the main linear accelerator, thereby allowing, in addition to providing variability in energy, to vary the capture by variations in power and phase between the first cavity and the remaining cavities in the initial set of cavities, thereby allowing variable current.

30. The linear accelerator according to claim 29, characterized in that For operation as a variable dose linear accelerator, the linear accelerator is configured such that the current to the main linear accelerator can be modified using only the buncher cavity by varying the phase and the amplitude of the first cavity.

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