Patent Publication Number: US-2023154716-A1

Title: Radiotherapy device and microwave source thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Application No. PCT/CN2021/087063, filed on Apr. 13, 2021, which claims priority of Chinese Patent Application No. 202110184055.2, filed on Feb. 10, 2021, Chinese Patent Application No. 202010731106.4, filed on Jul. 27, 2020, and Chinese Patent Application No. 202120513013.4, filed on Mar. 10, 2021, the contents of each of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure generally relates to a radiotherapy device, and more particularly, relates to a microwave source used in the radiotherapy device. 
     BACKGROUND 
     Radiation therapy is widely used in cancer treatment and also beneficial to several other health conditions. A radiotherapy device (e.g., a linear accelerator) is often utilized to perform the radiation therapy. In such a radiotherapy device, a microwave source including an anode block and a cathode is configured to produce microwave pulses (or radio frequency pulses) for controlling the generation of radiation beams (e.g., X-rays). The microwave source is an important component for the radiotherapy device. Therefore, it is desirable to improve the design of the microwave source used in such a radiotherapy device. 
     SUMMARY 
     According to an aspect of the present disclosure, a microwave source is provided. The microwave source may include a cathode heater and a thermionic emitter. The cathode heater may include a first component, and a second component enclosing at least a portion of the first component. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. At least a portion of the second component of the cathode heater may be in contact with the thermionic emitter. 
     In some embodiments, the at least a portion of the first component of the cathode heater may be in contact with the second component of the cathode heater. 
     In some embodiments, the at least a portion of the first component of the cathode heater may be embedded in the second component of the cathode heater. 
     In some embodiments, the first component of the cathode heater may be made of a high-melting-point and electrically conductive material. 
     In some embodiments, the second component of the cathode heater may be made of an electrically insulating material. 
     In some embodiments, the cathode heater may include a third component. The first component and the second component may be disposed between the third component and the thermionic emitter. 
     In some embodiments, the cathode heater may include at least one fourth component configured to increase a structural stability of the third component. 
     In some embodiments, the first component may be a double helix filament including a first filament and a second filament. When the first filament and the second filament are disposed in a magnetic field and powered by a power source, a first direction of a first current flow in the first filament may be opposite to a second direction of a second current flow in the second filament such that a first force on the first filament due to the magnetic field is in line with and in an opposite direction to a second force on the second filament due to the magnetic field. 
     In some embodiments, a first current value of the first current flow of the first filament and a second current value of the second current flow of the second filament may be equal. 
     In some embodiments, a direction of the magnetic field may be parallel to a filament axis direction of the double helix filament. 
     In some embodiments, a first diameter of the first filament may be less than a second diameter of the second filament along a direction perpendicular to the filament axis direction of the double helix filament. 
     In some embodiments, the first component may include one or more filaments. Each filament of the one or more filaments may be in a cylindrical configuration. When the first component is disposed in a magnetic field, a direction of the magnetic field may be parallel to an extending direction of the each filament of the one or more filaments. 
     In some embodiments, the first component may include a plurality of filaments arranged in a cage configuration. 
     In some embodiments, the microwave source may include a first connection member operably connected to a first end of the first component; and a second connection member operably connected to a second end of the first component. The first component may be powered by a power source via the first connection member and the second connection member. 
     In some embodiments, the thermionic emitter may include a substrate component and an electron emission layer. The cathode heater may be disposed inside the substrate component. The electron emission layer may be disposed on an outer wall of the substrate component that includes at least one discontinuity. 
     In some embodiments, the at least a portion of the second component of the cathode heater may be in contact with the substrate component. 
     In some embodiments, the electron emission layer may include at least one groove configured to cause the at least one discontinuity in the electron emission layer. 
     In some embodiments, the at least one groove may extend along an axial direction or a circumferential direction of the substrate component. 
     In some embodiments, the electron emission layer may include a plurality of grooves. The plurality of grooves may extend in a parallel direction and be equispaced. 
     In some embodiments, a cross section of one of the at least one groove may be rectangular, trapezoidal, or parallelogram. 
     In some embodiments, each of the at least one groove may include a side surface. The side surface and a surface of the electron emission layer may be arranged at an angle. 
     In some embodiments, the electron emission layer may include at least one first groove and at least one second groove. A first extending direction of the at least one first groove may be different from a second extending direction of the at least one second groove. 
     In some embodiments, the thermionic emitter further may include a filling layer disposed in the at least one groove. 
     In some embodiments, the substrate component may be of a cylindrical configuration. 
     In some embodiments, the substrate component may be made of molybdenum. 
     According to an aspect of the present disclosure, a microwave source is provided. The microwave source may include a cathode heater and a thermionic emitter. The cathode heater may include a double helix filament. The double helix filament may include a first filament and a second filament. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. When the first filament and the second filament are disposed in a magnetic field and powered by a power source, a first direction of a first current flow in the first filament may be opposite to a second direction of a second current flow in the second filament such that a first force on the first filament due to the magnetic field is in line with and in an opposite direction to a second force on the second filament due to the magnetic field. 
     In some embodiments, a first current value of the first current flow of the first filament and a second current value of the second current flow of the second filament may be equal. 
     In some embodiments, a direction of the magnetic field may be parallel to a filament axis direction of the double helix filament. 
     In some embodiments, a first diameter of the first filament may be less than a second diameter of the second filament along a direction perpendicular to the filament axis direction of the double helix filament. 
     In some embodiments, the cathode heater may further include a supporting component in which at least a portion of the first filament or the second filament are embedded. 
     In some embodiments, the supporting component may be made of an electrically insulating material. 
     In some embodiments, the first filament and the second filament may be integrated into a single filament. 
     In some embodiments, the first filament and the second filament may be two separate filaments. 
     According to an aspect of the present disclosure, a microwave source is provided. The microwave source may include a cathode heater and a thermionic emitter. The cathode heater may include one or more filaments. Each filament of the one or more filaments may be of a cylindrical configuration. Thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. When the cathode heater is disposed in a magnetic field, a direction of the magnetic field may be parallel to an extending direction of the each filament of the one or more filaments. 
     In some embodiments, the cathode heater may include a plurality of filaments arranged in a cage configuration. 
     In some embodiments, the microwave source may include a first connection member operably connected to a first end of the cathode heater, and a second connection member operably connected to a second end of the cathode heater. The cathode heater may be powered by a power source via the first connection member and the second connection member. 
     In some embodiments, the cathode heater may include a supporting component in which at least a portion of the first filament or the second filament are embedded. 
     In some embodiments, the supporting component may be made of an electrically insulating material. 
     According to an aspect of the present disclosure, a microwave source is provided. The microwave source may include a cathode heater and a thermionic emitter. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. The thermionic emitter may include a substrate component and an electron emission layer. The cathode heater may be disposed inside the substrate component. The electron emission layer may be disposed on an outer wall of the substrate component. The electron emission layer may include at least one discontinuity. 
     In some embodiments, the electron emission layer may include at least one groove configured to cause the at least one discontinuity in the electron emission layer. 
     In some embodiments, the at least one groove may extend along an axial direction or a circumferential direction of the substrate component. 
     In some embodiments, the electron emission layer may include a plurality of grooves. The plurality of grooves may extend in a parallel direction and be equispaced. 
     In some embodiments, a cross section of one of the at least one groove may be rectangular, trapezoidal, or parallelogram. 
     In some embodiments, each of the at least one groove may include a side surface, and the side surface and a surface of the electron emission layer are arranged at an angle. 
     In some embodiments, the electron emission layer may include at least one first groove and at least one second groove. A first extending direction of the at least one first groove may be different from a second extending direction of the at least one second groove. 
     In some embodiments, the thermionic emitter may further include a filling layer disposed in the at least one groove. 
     In some embodiments, the substrate component may be of a cylindrical configuration. 
     In some embodiments, the substrate component may be made of molybdenum. 
     According to an aspect of the present disclosure, a radiotherapy device is provided. The radiotherapy device may include a linear accelerator. The linear accelerator may include an electron generator configured to emit electrons along a beam path, and a microwave source configured to generate microwaves. The microwave source may include an anode block and a cathode centered in the anode block. The cathode may include a cathode heater and a thermionic emitter. The cathode heater may include a first component, and a second component enclosing at least a portion of the first component. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. At least a portion of the second component of the cathode heater may be in contact with the thermionic emitter. 
     According to an aspect of the present disclosure, a radiotherapy device is provided. The radiotherapy device may include a linear accelerator. The linear accelerator may include an electron generator configured to emit electrons along a beam path, and a microwave source configured to generate microwaves. The microwave source may include an anode block and a cathode centered in the anode block. The cathode may include a cathode heater and a thermionic emitter. The cathode heater may include a double helix filament. The double helix filament may include a first filament and a second filament. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. When the first filament and the second filament are disposed in a magnetic field and powered by a power source, a first direction of a first current flow in the first filament may be opposite to a second direction of a second current flow in the second filament such that a first force on the first filament due to the magnetic field is in line with and in an opposite direction to a second force on the second filament due to the magnetic field. 
     According to an aspect of the present disclosure, a radiotherapy device is provided. The radiotherapy device may include a linear accelerator. The linear accelerator may include an electron generator configured to emit electrons along a beam path, and a microwave source configured to generate microwaves. The microwave source may include an anode block and a cathode centered in the anode block. The cathode may include a cathode heater and a thermionic emitter. The cathode heater may include one or more filaments. Each filament of the one or more filaments may be of a cylindrical configuration. Thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. When the cathode heater is disposed in a magnetic field, a direction of the magnetic field may be parallel to an extending direction of the each filament of the one or more filaments. 
     According to an aspect of the present disclosure, a radiotherapy device is provided. The radiotherapy device may include a linear accelerator. The linear accelerator may include an electron generator configured to emit electrons along a beam path, and a microwave source configured to generate microwaves. The microwave source may include an anode block and a cathode centered in the anode block. The cathode may include a cathode heater and a thermionic emitter. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. The thermionic emitter may include a substrate component and an electron emission layer. The cathode heater may be disposed inside the substrate component. The electron emission layer may be disposed on an outer wall of the substrate component. The electron emission layer may include at least one discontinuity. 
     Additional features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The features of the present disclosure may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is further described in terms of exemplary embodiments. These exemplary embodiments are described in detail with reference to the drawings. The drawings are not to scale. These embodiments are non-limiting exemplary embodiments, in which like reference numerals represent similar structures throughout the several views of the drawings, and wherein: 
         FIG.  1    is a schematic diagram illustrating an exemplary medical system according to some embodiments of the present disclosure; 
         FIG.  2    is a schematic diagram illustrating exemplary components of a linear accelerator (linac) according to some embodiments of the present disclosure; 
         FIG.  3 A  illustrates a cross-sectional view of an exemplary microwave source (e.g., a magnetron) according to some embodiments of the present disclosure; 
         FIG.  3 B  illustrates different forms of an anode block in a microwave source according to some embodiments of the present disclosure; 
         FIG.  3 C  illustrates an exemplary profile of a cathode of a microwave source according to some embodiments of the present disclosure; 
         FIG.  4    is a schematic diagram illustrating an exemplary microwave source according to some embodiments of the present disclosure; 
         FIG.  5    is a schematic diagram illustrating an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  6    is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  7    is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  8 A  is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  8 B  is a top view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  9 A  is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIG.  9 B  is a top view of an exemplary cathode according to some embodiments of the present disclosure; 
         FIGS.  10 A and  10 B  are a schematic diagram illustrating an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  11    is an enlarged view of a cross-sectional region  1010  of the double helix filament  1000  shown in  FIG.  10 B  according to some embodiments of the present disclosure; 
         FIG.  12 A  is a schematic diagram illustrating an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  12 B  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  13 A  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  13 B  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  13 C  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure; 
         FIG.  14    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure; 
         FIG.  15    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure; 
         FIG.  16    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure; 
         FIGS.  17 A- 17 C  are schematic diagrams illustrating cross-sectional views of exemplary grooves according to some embodiments of the present disclosure; 
         FIG.  18    illustrates a cross-sectional view of an exemplary microwave source according to some embodiments of the present disclosure; and 
         FIG.  19    illustrates a cross-sectional view of an exemplary microwave source according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well-known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Also, the term “exemplary” is intended to refer to an example or illustration. 
     It will be understood that the terms “system,” “engine,” “unit,” “module,” and/or “block” used herein are one method to distinguish different components, elements, parts, sections or assembly of different levels in ascending order. However, the terms may be displaced by another expression if they achieve the same purpose. 
     Generally, the word “module,” “unit,” or “block,” as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or another storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or from themselves, and/or may be invoked in response to detected events or interrupts. Software modules/units/blocks configured for execution on computing devices may be provided on a computer-readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included in connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks, but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/subunits/sub-blocks despite their physical organization or storage. The description may be applicable to a system, an engine, or a portion thereof. 
     It will be understood that, although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of exemplary embodiments of the present disclosure. 
     Spatial and functional relationships between elements are described using various terms, including “connected,” “attached,” and “mounted.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the present disclosure, that relationship includes a direct relationship where no other intervening elements are present between the first and second elements, and also an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. In contrast, when an element is referred to as being “directly” connected, attached, or positioned to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). 
     These and other features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, may become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this disclosure. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to limit the scope of the present disclosure. It is understood that the drawings are not to scale. 
     The following description is provided with reference to exemplary embodiments that a medical device includes a microwave source (e.g., a magnetron) unless otherwise stated. However, it is understood that it is for illustration purposes only and not intended to limit the scope of the present disclosure. The microwave source disclosed herein may be suitable for other applications (e.g., a microwave oven, a particle accelerator, etc.). Merely by way of example, the medical device may include a radiotherapy device, such as an image-guided radiotherapy (IGRT) device. The IGRT device may include an imaging component (e.g., an MRI device, a PET device, a CT device) and a radiation therapy component (e.g., a linear accelerator). 
     An aspect of the present disclosure relates to a microwave source. The microwave source may include a cathode heater and a thermionic emitter. The cathode heater may include a first component (e.g., at least one filament), and a second component enclosing at least a portion of the first component. For example, the at least a portion of the first component of the cathode heater may be embedded in the second component of the cathode heater. The thermionic emitter may be configured to release electrons when the thermionic emitter is heated by the cathode heater. At least a portion of the second component of the cathode heater may be in contact with the therm ionic emitter. 
     Accordingly, the heat generated by the first component may be transferred to the second component, and then the heat may be transferred from the second component to the thermionic emitter. The heat loss in the heat transfer between the first component and the second component, and the heat loss in the heat transfer between the second component and the thermionic emitter may be relatively small due to the contact between the first component and the second component and the contact between the second component and the thermionic emitter, and the heat transfer efficiency may be relatively high. The volatilization rate of the material of the first component may be reduced, and the stability of the first component may be improved. Furthermore, the second component may limit (e.g., fix) the first component, which may effectively prevent the first component from moving. 
     In some embodiments, the cathode heater may include multiple filaments. The filaments may be arranged such that when the filaments are powered and placed in a magnetic field, the forces (e.g., electromagnetic forces) on the filaments are reduced or counterbalanced to reduce or avoid deformation of the filaments of the cathode heater, thereby prolonging the service life of the cathode heater and reduce or avoid the energy consumption caused by the existence of the forces. For instance, the cathode heater may include a double helix filament. The double helix filament may include a first filament and a second filament. When the first filament and the second filament are disposed in a magnetic field and powered by a power source, a first direction of a first current flow of the first filament may be opposite to a second direction of a second current flow of the second filament, such that a first force on the first filament due to the magnetic field is in line with and in an opposite direction to a second force on the second filament due to the magnetic field. In some embodiments, a first current value of the first current flow of the first filament and a second current value of the second current flow of the second filament may be equal. Accordingly, the first force on the first filament and the second force on the second filament may be (substantially) counterbalanced, which may reduce or avoid the deformation and/or prolong the service life of the cathode heater. Moreover, the energy consumption caused by the existence of the forces may be reduced or avoided. 
     As another example, the cathode heater may include a plurality of filaments. Each filament of the plurality of filaments may be of a cylindrical configuration. The plurality of filaments may be arranged in a cage configuration. When the plurality of filaments are disposed in a magnetic field and powered by a power source, a direction of a current flow of each filament of the plurality of filaments may be (substantially) parallel to a direction of the magnetic field such that the each filament is not subjected to a force due to the magnetic field, which may reduce or avoid the deformation and/or prolong the service life of the cathode heater. Moreover, the energy consumption caused by the existence of the forces may be reduced or avoided. 
     In some embodiments, the thermionic emitter may include a substrate component and an electron emission layer. The cathode heater may be disposed inside the substrate component. The electron emission layer may be disposed on an outer wall of the substrate component. The electron emission layer may include at least one discontinuity (e.g., at least one groove). Accordingly, the at least one discontinuity may provide a space for accommodating a deformation of the electron emission layer due to thermal expansion and contraction. The surface stress caused by the thermal expansion or an uneven surface temperature distribution of the electron emission layer may be alleviated by the at least one discontinuity. The risk of cracking of the electron emission layer may be reduced, and the electron emission efficiency of the thermionic emitter may be improved. The service life of the thermionic emitter may be prolonged. 
     Another aspect of the present disclosure relates to a radiotherapy device including a linear accelerator. The linear accelerator may include an electron generator and a microwave source. The electron generator may be configured to emit electrons. The microwave source may be configured to generate microwaves. The microwave source may include a cathode heater, a thermionic emitter, and an anode block, as described elsewhere in the present disclosure. Accordingly, the working stability of the radiotherapy device may be improved, and the service life of the radiotherapy device may be prolonged. 
       FIG.  1    is a schematic diagram illustrating an exemplary medical system according to some embodiments of the present disclosure. As illustrated, a medical system  100  may include a medical device  110 , a processing device  120 , a storage device  130 , a terminal  140 , and a network  150 . The components of the medical system  100  may be connected in one or more of various ways. Merely by way of example, as illustrated in  FIG.  1   , the medical device  110  may be connected to the processing device  120  directly as indicated by the bi-directional arrow in dotted lines linking the medical device  110  and the processing device  120 , or through the network  150 . As another example, the storage device  130  may be connected to the medical device  110  directly as indicated by the bi-directional arrow in dotted lines linking the medical device  110  and the storage device  130 , or through the network  150 . As still another example, the terminal  140  may be connected to the processing device  120  directly as indicated by the bi-directional arrow in dotted lines linking the terminal  140  and the processing device  120 , or through the network  150 . 
     In some embodiments, the medical device  110  may be a radiotherapy device. The radiotherapy device may be configured to deliver a radiation therapy treatment for cancers and other conditions. For example, the radiotherapy device may deliver one or more radiation beams to a treatment region (e.g., a tumor) of a subject (e.g., a patient) for causing an alleviation of the subject’s disease and/or symptoms. The subject may include any biological subject (e.g., a human being, an animal, a plant, or a portion thereof) and/or a non-biological subject (e.g., a phantom, structure/device to be non-destructively tested). In some embodiments, the radiotherapy device may be a conformal radiation therapy device, an image guided radiation therapy (IGRT) device, an intensity modulated radiation therapy (IMRT) device, an intensity modulated arc therapy (IMAT) device, or the like. 
     In some embodiments, the medical device  110  may include a linear accelerator (also referred to as “linac”)  111 . The linac  111  may generate and emit a radiation beam (e.g., an X-ray beam) from a treatment head  112 . The radiation beam may go through one or more collimators (e.g., a primary collimator and/or a multi-leaf collimator (MLC)) of certain shapes, and enter into the subject. In some embodiments, the radiation beam may include electrons, photons, or other types of radiation. In some embodiments, the energy of the radiation beam may be in the megavoltage range (e.g., &gt;1 MeV), and may therefore be referred to as megavoltage beam. The treatment head  112  may be coupled to a gantry  113 . The gantry  113   may rotate, for example, clockwise or counter-clockwise around a gantry rotation axis  114 . The treatment head  112  may rotate along with the gantry  113 . In some embodiments, the medical device  110  may include an imaging element  115 . The imaging element  115  may receive the radiation beam that passes through the subject, and generate images of patients and/or phantoms before, during and/or after a radiation treatment or a correction process based on received radiation beam. The imaging element  115  may include an analog detector, a digital detector, or the like, or a combination thereof. The imaging element  115  may be connected to the gantry  113  in any connection means, including an extendible housing. Thus, the rotation of the gantry  113  may cause the treatment head  112  and the imaging element  115  to rotate in a coordinated manner. In some embodiments, the medical device  110  may also include a table  116 . The table  116  may support the subject during a radiation treatment or imaging, and/or support a phantom during a correction process of the medical device  110 . The table  116  may be adjustable to suit for different application scenarios. 
     The processing device  120  may process data and/or information obtained from the medical device  110 , the storage device  130 , and/or the terminal(s)  140 . In some embodiments, the processing device  120  may perform one or more radiotherapy operations. For example, the processing device  120  may process plan data (e.g., from a treatment planning system (TPS)), and determine motion parameters that may be used to control the motions of multiple components in the medical device  110 . In some embodiments, the processing device  120  may be a single server or a server group. The server group may be centralized or distributed. In some embodiments, the processing device  120  may be local or remote. For example, the processing device  120  may access information and/or data from the medical device  110 , the storage device  130 , and/or the terminal(s)  140  via the network  150 . As another example, the processing device  120  may be directly connected to the medical device  110 , the terminal(s)  140 , and/or the storage device  130  to access information and/or data. In some embodiments, the processing device  120  may be implemented on a cloud platform. For example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or a combination thereof. In some embodiments, the processing device  120  may be part of the terminal  140 . In some embodiments, the processing device  120  may be part of the medical device  110 . 
     The storage device  130  may store data, instructions, and/or any other information. In some embodiments, the storage device  130  may store data obtained from the medical device  110 , the processing device  120 , and/or the terminal(s)  140 . The data may include image data acquired by the processing device  120 , algorithms and/or models for processing the image data, etc. For example, the storage device  130  may store an image of a subject obtained from a medical device (e.g., the medical device  110 ). In some embodiments, the storage device  130  may store data and/or instructions that the processing device  120  and/or the terminal  140  may execute or use to perform exemplary methods described in the present disclosure. In some embodiments, the storage device  130  may include a mass storage, removable storage, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. Exemplary mass storage may include a magnetic disk, an optical disk, a solid-state drive, etc. Exemplary removable storage may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. Exemplary volatile read-and-write memories may include a random-access memory (RAM). Exemplary RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. Exemplary ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage device  130  may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. 
     In some embodiments, the storage device  130  may be connected to the network  150  to communicate with one or more other components in the medical system  100  (e.g., the processing device  120 , the terminal(s)  140 ). One or more components in the medical system  100  may access the data or instructions stored in the storage device  130  via the network  150 . In some embodiments, the storage device  130  may be integrated into the medical device  110 . 
     The terminal(s)  140  may be connected to and/or communicate with the medical device  110 , the processing device  120 , and/or the storage device  130 . In some embodiments, the terminal  140  may include a mobile device  141 , a tablet computer  142 , a laptop computer  143 , or the like, or any combination thereof. For example, the mobile device  141  may include a mobile phone, a personal digital assistant (PDA), a gaming device, a navigation device, a point of sale (POS) device, a laptop, a tablet computer, a desktop, or the like, or any combination thereof. In some embodiments, the terminal  140  may include an input device, an output device, etc. The input device may include alphanumeric and other keys that may be input via a keyboard, a touchscreen (for example, with haptics or tactile feedback), a speech input, an eye tracking input, a brain monitoring system, or any other comparable input mechanism. Other types of the input device may include a cursor control device, such as a mouse, a trackball, or cursor direction keys, etc. The output device may include a display, a printer, or the like, or any combination thereof. 
     The network  150  may include any suitable network that can facilitate the exchange of information and/or data for the medical system  100 . In some embodiments, one or more components of the medical system  100  (e.g., the medical device  110 , the processing device  120 , the storage device  130 , the terminal(s)  140 , etc.) may communicate information and/or data with one or more other components of the medical system  100  via the network  150 . For example, the processing device  120  and/or the terminal  140  may obtain information stored in the storage device  130  via the network  150 . The network  150  may be and/or include a public network (e.g., the Internet), a private network (e.g., a local area network (LAN), a wide area network (WAN)), etc.), a wired network (e.g., an Ethernet network), a wireless network (e.g., an 802.11 network, a Wi-Fi network, etc.), a cellular network (e.g., a Long Term Evolution (LTE) network), a frame relay network, a virtual private network (VPN), a satellite network, a telephone network, routers, hubs, switches, server computers, and/or any combination thereof. For example, the network  150  may include a cable network, a wireline network, a fiber-optic network, a telecommunications network, an intranet, a wireless local area network (WLAN), a metropolitan area network (MAN), a public telephone switched network (PSTN), a Bluetooth™ network, a ZigBee™ network, a near field communication (NFC) network, or the like, or any combination thereof. In some embodiments, the network  150  may include one or more network access points. For example, the network  150  may include wired and/or wireless network access points such as base stations and/or internet exchange points through which one or more components of the medical system  100  may be connected to the network  150  to exchange data and/or information. 
     This description is intended to be illustrative, and not to limit the scope of the present disclosure. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. However, those variations and modifications do not depart the scope of the present disclosure. In some embodiments, two or more components of the medical system  100  may be integrated into a single component. In some embodiments, a component of the medical system  100  may be implemented on two or more subcomponents. Additionally or alternatively, the medical system  100  may include one or more additional components and/or one or more components of the medical system  100  described above may be omitted. 
       FIG.  2    is a schematic diagram illustrating exemplary components of a linear accelerator (linac) according to some embodiments of the present disclosure. In some embodiments, a linac  200  illustrated in  FIG.  2    may be implemented on a radiotherapy device. 
     Linear Accelerators (also called “LINACS”) may be widely used for a variety of tasks in a broad range of applications, including industrial applications such as non-destructive testing (NDT), security inspection (SI), radiotherapy (RT), electron beam processing-sterilization, and polymer curing. Both accelerated electron beams, and bremsstrahlung X-ray beam generated by such electron beams striking a conversion target at the end of an accelerating channel, may be used for various tasks. The type of radiation beam selected may be typically determined by the specific application and its requirements. In many applications, the requirements may include energy variation and dose rate variation of the radiation beam, including broad RB energy variation, for example, from 0.5 MeV to a maximum energy, which typically does not exceed 10 MeV due to neutron production and activation problems. However, in some cases, it can reach as high as 12 MeV, 15 MeV, 20 MeV, or even higher energies. 
     As illustrated in  FIG.  2   , the linac  200  may include a power supply  202 , a modulator  204 , an electron generator  206 , a microwave source  208 , an accelerator tube  210 , and a treatment head  212 . In some embodiments, the power supply  202  may be configured to provide high voltages (e.g., 45 kV) required for proper modulator operation. In some embodiments, the power supply  202  may include an alternating current (AC) circuit for supplying the alternating current voltage (ACV). In some embodiments, the power supply  202  may include a direct-current (DC) circuit for supplying the direct current voltage (DCV). The modulator  204  may be configured to simultaneously provide high voltage pulses (e.g., DC pulses) to the electron generator  206  and the microwave source  208 . The electron generator  206  (e.g., an electron gun, or an electron emitter) may produce electrons injected into the accelerator tube  210 . For example, the electron generator  206  may produce electrons along a range of angles and emit the electrons along a beam path. The electron beam may be injected into the accelerator tube  210 . The electrons in the accelerator tube  210  may be accelerated at one or more ranges of kinetic energy using microwaves at one or more ranges of frequency. The accelerated electrons may be transmitted to the treatment head  212  for generating a radiation beam. For example, the accelerated electrons may strike a target (e.g., an X-ray target) to generate the radiation beam (e.g., X-ray beam). The radiation beam may go through one or more collimators (e.g., a primary collimator and/or a multi-leaf collimator (MLC)) of certain shapes to form a collimated radiation beam. The collimated radiation beam may irradiate a subject (e.g., a lesion of a subject) to implement radiotherapy. 
     In some embodiments, the microwave source  208  may be configured to generate the microwaves at one or more ranges of frequency. The microwave source  208  may be deemed as an oscillator that transforms the DC pulses from the modulator  204  into microwave pulses. In some embodiments, the microwave source  208  may be a magnetron or a klystron. In some embodiments, the microwave source  208  may include a magnetron (also referred to as single-cathode magnetron) composed of one cathode and one anode block. In some embodiments, the microwave source  208  may include a magnetron (also referred to as multi-cathode magnetron) composed of multiple cathodes and one anode block. The multiple cathodes may share the same anode block. Through different arrangements of the cathode and the anode block, the microwave sources  208  may output different microwave powers. 
     In some embodiments, the microwave source  208  may be a magnetron. In the magnetron, the thermionic emitter may be heated by a cathode heater. The cathode heater may include at least one filament. The electrons released from the thermionic emitter may be accelerated toward the anode block by the action of pulsed DC electric field. The anode block may include a plurality of resonant cavities. In some embodiments, at least one electromagnet may be disposed surrounding the anode block. A static magnetic field may be applied perpendicular to a cross-section plane of the plurality of resonant cavities. The released electrons can move in complex spirals toward the resonant cavities due to influence of the magnetic field. A resonance effect (or the resonance phenomenon) may occur when the resonant cavities begin to resonate at a certain resonance frequency (e.g., 3000 MHz). Thus, the resonant cavities may emit microwaves. The microwaves may be transmitted to the accelerator tube  210  through a transmission waveguide. The electrons in the accelerator tube  210  may be accelerated by the microwave power. More descriptions regarding components of the microwave source may be found elsewhere in the present disclosure (e.g.,  FIG.  3 A- 19   , and the descriptions thereof). 
       FIG.  3 A  illustrates a cross-sectional view of an exemplary microwave source (e.g., a magnetron) according to some embodiments of the present disclosure. 
     As shown in  FIG.  3 A , a microwave source  300  may include an anode block  310  and a cathode  320  centered in the anode block  310 . The anode block  310  and the cathode  320  may be coaxial. In some embodiments, the anode block  310  may be fabricated into a cylindrical metal block (e.g., a copper block). The anode block  310  may include a plurality of resonant cavities  312 . For different microwave sources, the number of the resonant cavities may be different. In some embodiments, the number of the resonant cavities may be from 8 to 20. Merely for illustration, the anode block  310  includes eight resonant cavities  312 , that are, eight cylindrical holes around the cathode  320 . An interaction space may be formed between the anode block  310  and the cathode  320 , such as an open space between the anode block  310  and the cathode  320 . In the interaction space, the electric and magnetic fields interact to exert force upon the electrons. The magnetic field is usually provided by a strong, permanent magnet mounted around the microwave source  300  so that the magnetic field is parallel with the axis of the cathode. The electrons released from the cathode  320  may travel outwardly in the interactive space. The released electrons can be accelerated toward to the anode block  310  by the action of pulsed DC electric field. The electrons may move in complex spirals towards the resonant cavities  312  due to the magnetic field. In some embodiments, the resonant cavities  312  may exist in various shapes, for example, include but not limited to a semicircular-shape cavity, a circular-shape cavity, a square-shape cavity, a rectangular-shape cavity, a fan-shape cavity, or the like, or any combination thereof. 
       FIG.  3 B  illustrates different forms of an anode block in a microwave source according to some embodiments of the present disclosure. As illustrated in  FIG.  3 B , an anode block  310   a  may include a plurality of hole-and-slot type of resonant cavities  312   a , an anode block  310   b  may include a plurality of slot-type of resonant cavities  312   b , and an anode block  310   c  may include a plurality of vane-type of resonant cavities  312   c . The resonant cavities may be usually arranged in a radial fashion. 
       FIG.  3 C  illustrates an exemplary profile of a cathode of a microwave source according to some embodiments of the present disclosure. As illustrated in  FIG.  3 C , the cathode  320  may include a hollow dumbbell-shape structure. In some embodiments, the cathode  320  may be made up of a hollow cylinder of emissive material (e.g., Barium oxide) surrounding a cathode heater. For example, the cathode  320  may include a cathode heater and a thermionic emitter. The cathode heater may include at least one filament. The thermionic emitter may be made up of the hollow cylinder of emissive material. When the cathode heater is heated by a power source, the outer thermionic emitter may release electrons due to a thermionic emission resulting from the heat radiation. Then the released electrons may travel outwardly in the direction of the anode block. As the electrons nip past the resonant cavities of the anode block, the energy may be passed to the resonant cavities, thus the resonant cavities may resonant at a certain resonant frequency and radiate energy in the form of microwaves. 
       FIG.  4    is a schematic diagram illustrating an exemplary microwave source according to some embodiments of the present disclosure. As illustrated in  FIG.  4   , a microwave source  400  may include a cathode heater  411 , a thermionic emitter  412 , and an anode block  420 . The cathode heater  411  and the thermionic emitter  412  collectively may also be referred to as a cathode  410 . 
     The cathode heater  411  may be configured to heat the thermionic emitter  412 . In some embodiments, the cathode heater  411  may include a first component  4111  and a second component  4113 . The first component  4111  may be configured to generate heat. For example, after the first component  4111  is powered by a power source (e.g., a voltage (e.g., 20 V) or a current (e.g., 15 A) is applied to the first component  4111 ), the first component  4111  may generate heat, and the heat may be transferred from the first component  4111  to the second component  4113 . The heat may then be transferred from the second component  4113  to the thermionic emitter  412 . 
     In some embodiments, the first component  4111  may include at least one filament. The filament may be made of a high-melting-point (e.g., &gt;2000° C.) and electrically conductive material. Exemplary materials of the first component  4111  may include tungsten, molybdenum, rhenium, an alloy thereof (e.g., a tungsten-rhenium alloy), or the like, or any combination thereof. Merely by way of example, the first component  4111  may be made of a tungsten-rhenium alloy. Since the tungsten-rhenium alloy has a relatively high melting point, the first component  4111  made of the tungsten-rhenium alloy may tolerate a high temperature, undergoing little or no deformation and/or volatilization at the high temperature. 
     In some embodiments, the first component  4111  may include a single helix filament (e.g., a first component  5111  illustrated in  FIG.  5   ), a double helix filament (e.g., a double helix filament  1000  illustrated in  FIGS.  10 A,  10 B, and  11   ), one or more filaments of a columnar configuration (e.g., a cylindrical configuration) (e.g., a first component  4111  illustrated in  FIG.  4   , a first component  8111  illustrated in  FIGS.  8 A,  8 B,  9 A, and  9 B ), a plurality of filaments arranged in a cage configuration (e.g., a plurality of filaments  1210  illustrated in  FIGS.  12 A, and  12 B ), or the like. For example, as illustrated in  FIG.  4   , the first component  4111  may include a filament of a cylindrical configuration. More descriptions of the filament may be found elsewhere in the present disclosure (e.g.,  FIGS.  10 A- 13 C , and descriptions thereof). In some embodiments, a cross section of the filament may be circular, rectangular, trapezoidal, elliptical, etc. 
     The second component  4113  may be configured to electrically insulate the first component  4111  from the thermionic emitter  412 . In some embodiments, the second component  4113  may have a cylindrical shape, a conical shape, a rectangular shape, a spiral shape, or the like. In some embodiments, the second component  4113  may be made of a high temperature resistant and electrically insulating material. Exemplary materials of the second component  4113  may include ceramic materials, mica materials, or the like, or any combination thereof. Exemplary ceramic materials may include oxide ceramics (e.g., alumina ceramics), nitride ceramics (e.g., silicon nitride ceramics), carbide ceramics (e.g., silicon carbide ceramics), or the like. Merely by way of example, the second component  4113  may be made of a ceramic material. The ceramic material may have a desirable thermal conductivity such that the second component  4113  can conduct the heat emitted by the first component  4111  to the thermionic emitter  412  efficiently to avoid or minimize heat accumulation in the first component  4111 . Therefore, the stability of the first component  4111  may be improved. In addition, the ceramic material may have a desirable strength and high temperature resistance, which may ensure the stability of the cathode heater  411  during operation. 
     In some embodiments, the second component  4113  may enclose at least a portion of the first component  4111 . As used herein, “a component B enclosing a component A” refers to that the component B surrounds the component A such that the component A is separated from other components, e.g., the component A not touching or in contact with a component other than the component B. In some embodiments, the at least a portion of the first component  4111  may be in contact with the second component  4113 . For example, as illustrated in  FIG.  4   , at least a portion of the first component  4111  may be embedded in the second component  4113 , and the first component  4111  is not in contact with the thermionic emitter  412 . The heat generated by the first component  4111  may be transferred to the second component  4113  efficiently to avoid or minimize heat accumulation in the first component  4111 . The heat loss in the heat transfer between the first component  4111  and the second component  4113  may be relatively small, and the heat transfer efficiency may be relatively high. Since the first component  4111  is embedded in the second component  4113 , the volatilization rate of the material of the first component  4111  may be reduced, and the stability of the first component  4111  may be improved. Furthermore, the second component  4113  may provide mechanical support for (e.g., fix) the first component  4111 , which may effectively prevent the first component  4111  from moving. 
     The thermionic emitter  412  may be configured to release electrons when the thermionic emitter  412  is heated by the cathode heater  411 . For example, when the cathode heater  411  is heated by a power source, the thermionic emitter  412  may release electrons due to a thermionic emission resulting from thermal radiation. Then the released electrons may travel outwardly in the direction of the anode block  420 , as described elsewhere in the present disclosure (e.g.,  FIGS.  2 ,  3   , and the descriptions thereof). 
     In some embodiments, the thermionic emitter  412  may be made of metal. Exemplary metals may include tungsten, molybdenum, or the like. In some embodiments, a thermionic emission material may be coated on a surface of the thermionic emitter  412 . Exemplary thermionic emitter materials may include nickel, molybdenum, or the like, or an alloy thereof. Exemplary thermionic emission materials may include alkaline earth metal oxides, or the like. In some embodiments, the thermionic emitter  412  may have a porous structure (e.g., a honeycomb structure). The thermionic emission material may be filled in a plurality of pores of the thermionic emitter  412 . Exemplary thermionic emitter materials may include molybdenum, tungsten, a tungsten-iridium alloy, a tungsten-osmium alloy, or the like, or any combination thereof. Exemplary thermionic emission materials may include alkaline earth metal aluminate, scandate, or the like, or any combination thereof. When external heat energy is applied to the thermionic emission material so that the thermal energy input to a charge carrier overcomes the work function of the thermionic emission material, electrons may be emitted from the surface of the thermionic emission material. The thermionic emitter  412  may have any suitable shape. For example, the thermionic emitter  412  may have the shape of a hollow cylinder with a cavity. The cathode heater  411  may be disposed in the cavity of the thermionic emitter  412 . 
     In some embodiment, the thermionic emitter  412  may include a substrate component (e.g., a substrate component  7121  illustrated in  FIGS.  6 - 7   , a substrate component  8121  illustrated in  FIGS.  8 A,  8 B,  9 A, and  9 B , a substrate component  1410  illustrated in  FIG.  14   ), and an electron emission layer (e.g., an electron emission layer  7122  illustrated in  FIGS.  6 - 7   , an electron emission layer  8122  illustrated in  FIGS.  8 A,  8 B,  9 A, and  9 B , an electron emission layer  1420  illustrated in  FIG.  14   ). More descriptions of the substrate component and the electron emission layer may be found elsewhere in the present disclosure (e.g.,  FIG.  14 - 17 C , and the descriptions thereof). 
     In some embodiments, at least a portion of the second component  4113  may be in contact with the thermionic emitter  412 . For example, the at least a portion of the second component  4113  may be in contact with the substrate component of the thermionic emitter  412 . 
     According to some embodiments of the present disclosure, by disposing the second component  4113  between the first component  4111  and the thermionic emitter  412 , the second component  4113  may facilitate the heat transfer between the first component  4111  and the thermionic emitter  412 . Compared with the heat transfer between the first component  4111  and the thermionic emitter  412  via thermal radiation, the heat transfer efficiency between the first component  4111  and the thermionic emitter  412  via the second component  4113  may be relatively high. 
     In addition, the first component  4111  may be in contact with the second component  4113 , and the second component  4113  may be in contact with the thermionic emitter  412 . The temperature difference between the first component  4111  and the second component  4113 , and the temperature difference between the second component  4113  and the thermionic emitter  412  may be relatively small (e.g., less than 200° C.). Therefore, the required heating temperature of the first component  4111  may be relatively low, and the voltage required to heat the first component  4111  to the required heating temperature may also be relatively low. For example, during the operation of the thermionic emitter  412 , the thermionic emitter  412  needs to be maintained at a constant high temperature (e.g., 800° C., 1000° C.). In a traditional cathode, the temperature difference between the filament and a thermionic emitter may be relatively high (e.g., greater than 700° C.). That is, the required heating temperature of the filament may be higher than 1700° C. such that the thermionic emitter can be maintained at 1000° C. for operation. However, by using the cathode disclosed in the present disclosure, the required heating temperature of the filament (i.e., the first component  4111 ) may be around (e.g., less than) 1200° C. to maintain the temperature of the thermionic emitter at 1000° C. for operation. 
     The reduction of the required heating temperature of the filament may reduce the fatigue of filament material, and reduce the volatilization rate of the filament material, thereby increasing the service life of the filament. Furthermore, the filament material volatilized at high temperature may condense in a low temperature place, which may decrease the insulation performance of the second component  4113 . 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. 
       FIG.  5    is a schematic diagram illustrating an exemplary cathode according to some embodiments of the present disclosure. A cathode  500  may be similar to the cathode  410 , except for certain features described below. 
     As illustrated in  FIG.  5   , the cathode  500  may include a cathode heater  511  and a thermionic emitter  512 . The cathode heater  511  may include a first component  5111  and a second component  5113 . The first component  5111  may include a filament of a helix configuration. That is, the filament may be spirally wound to form a helix filament. Compared with a filament of a cylindrical configuration, the length of the helix filament in a limited space of the thermionic emitter  512  may be greater, the resistance of the helix filament to a current flow may be greater, and more electric energy may be generated and then converted into thermal energy. Therefore, the heating power of the helix filament may be relatively high. 
     At least a portion of the first component  5111  may be embedded in the second component  5113 . At least a portion of the second component  5113  may be in contact with the thermionic emitter  512 . The second component  5113  may be similar to the second component  4113 . The thermionic emitter  512  may be similar to the thermionic emitter  412 . 
       FIG.  6    is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure.  FIG.  7    is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure. 
     As illustrated in  FIG.  6   , a cathode  600  may include a cathode heater  711  and a thermionic emitter  712 . The cathode heater  711  may include a first component  7111  and a second component  7113 . The first component  7111  may include a filament of a helix configuration (e.g., a single helix filament, a double helix filament). The second component  7113  may have a first cylindrical structure with a hollow cavity. At least a part of the first component  7111  may be embedded in the second component  7113 . For example, the first component  7111  may be fully embedded in the second component  7113 . 
     In some embodiment, the thermionic emitter  712  may include a substrate component  7121  and an electron emission layer  7122 . The substrate component  7121  may be configured to support the electron emission layer  7122 . The substrate component  7121  may be made of molybdenum, tungsten, rhenium, or the like, or any combination thereof. The electron emission layer  7122  may be configured to release electrons when the electron emission layer  7122  is heated by the cathode heater  711 . In some embodiments, the electron emission layer  7122  may be disposed on an outer wall of the substrate component  7121 . In some embodiments, the electron emission layer  7122  may be made of a thermionic emission material as described elsewhere in the present disclosure. 
     In some embodiments, the substrate component  7121  may have a second cylindrical structure with a hollow cavity. The substrate component  7121  may be disposed on the outside of the first cylindrical structure of the second component  7113 . In some embodiments, at least a portion of an inner wall of the second cylindrical structure of the substrate component  7121  may be in contact with an outer wall of the first cylindrical structure of the second component  7113 . For example, all of the inner wall of the second cylindrical structure of the substrate component  7121  may be in contact with the outer wall of the first cylindrical structure of the second component  7113 . 
     In some embodiments, a difference between an outer diameter of the first cylindrical structure of the second component  7113  and an inner diameter of the second cylindrical structure of the substrate component  7121  may be less than a threshold (e.g., 0.1 mm, 0.5 mm). Accordingly, the second cylindrical structure of the substrate component  7121  may be snugly fit the first cylindrical structure of the second component  7113  so that the inner wall of the second cylindrical structure of the substrate component  7121  may be in contact with the outer wall of the first cylindrical structure of the second component  7113 . More descriptions of the substrate component and the electron emission layer may be found elsewhere in the present disclosure (e.g.,  FIGS.  14 - 17 C , and descriptions thereof). 
     According to some embodiments of the present disclosure, the first component  7111  may be embedded in the second component  7113  such that the first component  7111  may be in contact with the second component  7113 . The heat generated by the first component  7111  may be transferred to the second component  7113  efficiently. The second component  7113  may be in contact with the thermionic emitter  712 , and the heat may be transferred from the second component  7113  to the thermionic emitter  712  efficiently. Therefore, the efficiency of the heat transfer between the cathode heater  711  and the thermionic emitter  712  may be improved. 
     In addition, the required heating temperature of the first component  7111  may be relatively low, the volatilization rate of the first component  7111  may be reduced, and the stability of the first component  7111  may be improved. The service life of the first component  7111  may be prolonged. Furthermore, the second component  7113  may provide mechanical support for (e.g., fix) the first component  7111 , which may effectively prevent the first component  7111  from moving. 
     In some embodiments, as illustrated in  FIG.  7   , the cathode heater  711  may include a third component  720 . The third component  720  may be configured to facilitate the manufacturing of the second component  7113 . The first component  7111  and the second component  7113  may be disposed between the third component  720  and the substrate component  7121  of the thermionic emitter  712 . The third component  720  may be made of a high-melting-point (e.g., &gt;2000° C.) material. Exemplary materials of the third component  720  may include tungsten, molybdenum, rhenium, or the like, or an alloy thereof, or any combination thereof. In some embodiments, the third component  720  may have a third cylindrical structure. 
     In some embodiments, during the manufacturing process of the cathode heater  711 , the third component  720  may be supported in (e.g., one or more notches of) the cavity of the substrate component  7121 . For instance, on the inner wall of the substrate component  7121  forming the cavity, there may be one or more notches configured to facilitate the positioning of the third component  720  in the cavity of the substrate component  7121 . The first component  7111  of a desired shape and the material of the second component  7113  (e.g., ceramic powders) may be disposed between the third component  720  and the substrate component  7121 . Then the material of the second component  7113  (e.g., ceramic powders) may be molded (e.g., sintered) to form the cathode heater  711 . For example, after the third component  720  is positioned in the cavity of the substrate component  7121 , a tungsten filament of a cylindrical configuration and ceramic powders may be disposed between the third component  720  and the substrate component  7121 . Then the ceramic powders may be sintered to form the second component  7113 . In this situation, the first component  7111  may be in contact with the second component  7113 , and the efficiency of the heat transfer between the first component  7111  and the second component  7113  may be relatively high. 
     In some embodiments, an inner cavity (e.g., one or more holes, a cylindrical cavity, a helix cavity) that can accommodate the first component  7111  in (a wall of) the second component  7113  may be formed during the manufacturing process (e.g., molding process) of the second component  7113 . After the second component  7113  is formed (e.g., molded), the first component  7111  may be disposed in the inner cavity of the second component  7113 . For example, after the third component  720  is supported in the cavity of the substrate component  7121 , a mold of a cylindrical configuration and ceramic powders may be disposed between the third component  720  and the substrate component  7121 . Then the ceramic powders may be molded (e.g., sintered) to form the second component  7113 . The mold may be taken out of the second component  7113 , and a cylindrical cavity may be formed in (the wall of) the second component  7113 . Then a tungsten filament of a cylindrical configuration may be placed in the cylindrical cavity of the second component  7113 . In this situation, a gap between the first component  7111  and the second component  7113  may exist, which may provide room for the thermal expansion and deformation of the materials of the first component  7111  and the second component  7113 . 
     In some embodiments, after the molding process (e.g., sintering process) of the second component  7113  is completed, the third component  720  may be disassembled from (one or more notches of) the cavity of the substrate component  7121 . In this situation, the weight of the cathode  600  may be reduced, and the heating rate of the cathode  600  may be increased. 
     In some embodiments, after the molding process (e.g., sintering process) of the second component  7113  is completed, the third component  720  may remain in the cavity of the substrate component  7121 . For example, before the molding process (e.g., sintering process) of the second component  7113  and after the third component  720  is positioned in the cavity of the substrate component  7121  via one or more notches on the inner wall of the substrate component  7121  that forms the cavity, a solder may be filled in the one or more notches. During the molding process (e.g., sintering process), the third component  720  may be welded to the substrate component  7121 . In this situation, the configuration of the third component  720  may prevent a piece of insulating material of the second component  7113  peeled off due to thermal expansion and contraction from falling into an anode vacuum chamber through a vent hole  750 . 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the first component  7111  may have any shape. For example, the first component  7111  may include a plurality of filaments. Each filament may be of a cylindrical configuration, as described elsewhere in the present disclosure (e.g.,  FIGS.  4 ,  8 A,  8 B,  9 A,  9 B,  12 A,  12 B,  13 A- 13 C , and descriptions thereof). 
     In some embodiments, the cathode heater  711  may be manufactured according to different manufacturing processes. In some embodiments, a mold may be disposed on the first component  7111 , and the material of the second component  7113  (e.g., ceramic powders) may be injected into the mold. Then the material of the second component  7113  may be sintered to prepare the cathode heater  711 . In some embodiments, after the cathode heater  711  is manufactured, the cathode heater  711  may be disposed inside the substrate component  7121  of the thermionic emitter  712 . For example, after the cathode heater  711  is manufactured, the cathode heater  711  may be disposed between the substrate component  7121  of the thermionic emitter  712  and the third component  720 . 
     In some embodiments, the first component  7111  may be disposed in the cavity of the first cylindrical structure of the second component  7113 . For example, the first component  7111  may be in contact with the inner wall of the cavity of the second component  7113 , in order to reduce the heat loss in the heat transfer between the first component  7111  and the second component  7113 . As another example, the first component  7111  may be separated from, and therefore not in contact with, the inner surface of the cavity of the second component  7113 , and a gap between the first component  7111  and the second component  7113  may be formed, which may provide room for the thermal expansion and deformation of the materials of the first component  7111  and the second component  7113 . 
       FIG.  8 A  is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure.  FIG.  8 B  is a top view of an exemplary cathode according to some embodiments of the present disclosure.  FIG.  9 A  is an axial sectional view of an exemplary cathode according to some embodiments of the present disclosure.  FIG.  9 B  is a top view of an exemplary cathode according to some embodiments of the present disclosure. A cathode  800  may be similar to the cathode  600 , except for certain features described below. 
     As illustrated in  FIGS.  8 A, and  8 B , the cathode  800  may include a cathode heater  811  and a thermionic emitter  812 . The cathode heater  811  may include a first component  8111  and a second component  8113 . The first component  8111  may include a plurality of filaments. Each filament may be of a cylindrical configuration. The second component  8113  may have a cylindrical structure with a cavity. The plurality of filaments may be embedded in and arranged along the sidewall of the cylindrical structure of the second component  8113  as illustrated in  FIG.  8 B . At least a part of the first component  8111  may be embedded in the second component  8113 . The thermionic emitter  812  may include a substrate component  8121  and an electron emission layer  8122 . The substrate component  8121  may be similar to the substrate component  7121 . The electron emission layer  8122  may be similar to the electron emission layer  7122 . 
     In some embodiments, as illustrated in  FIGS.  9 A and  9 B , the cathode heater  811  may include a third component  820 . The third component  820  may include a plurality of chambers. For example, the third component  820  may include a first chamber  820 - 1  and a second chamber  820 - 2 . The first chamber  820 - 1  and the second chamber  820 - 2  may be connected via a fourth component  830 . The fourth component  830  may have any suitable structure. In some embodiments, the fourth component  830  may have a cylindrical structure. The fourth component  830  may increase the structural stability of the third component  820 . For example, the fourth component  830  may prevent the third component  820  from deformation during the sintering process of the second component  8113 . Merely by way of example, the fourth component  830  may have a cylindrical structure with a cavity (e.g., a cylindrical structure with a through hole). Accordingly, gas in the first chamber  820 - 1  and the second chamber  820 - 2  may be circulated via the fourth component  830 , which may ensure the vacuum degree of a microwave source, and improve the performance of the microwave source. The fourth component  830  may be made of a high-melting-point (e.g., &gt;1000° C.) material as described elsewhere in the present disclosure. 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the third component  820  and/or the fourth component  830  may be omitted. In some embodiments, the third component  820  may have a similar structure to the third component  720  illustrated in  FIG.  7   . In some embodiments, the third component  720  may have a similar structure to the third component  820  illustrated in  FIG.  8   . In some embodiments, the first component  8111  may have any shape. For example, the first component  8111  may include a filament of a helix configuration (e.g., a single helix filament, a double helix filament) as described elsewhere in the present disclosure. 
       FIGS.  10 A and  10 B  are a schematic diagram illustrating an exemplary cathode heater according to some embodiments of the present disclosure. 
     As illustrated in  FIGS.  10 A and  10 B , a cathode heater may include a double helix filament  1000 . The double helix filament  1000  may be disposed in a magnetic field B. In some embodiments, the magnetic field B may be generated by a microwave source as described in  FIG.  3   . The magnetic field B may be of a certain strength and direction. In some embodiments, a direction of the magnetic field B may be (substantially) parallel to a filament axis direction A of the double helix filament  1000 . As used herein, a filament axis direction of a double helix filament refers to an extension direction of the double helix filament. As used herein, “substantially” indicates that the deviation is below a threshold (e.g., 5%, 10%, 15%, 20%, 30%, etc.). For instance, a direction being substantially parallel to an axis (or another direction) indicates that the deviation of the angle between the direction and the axis (or the other direction) from zero degrees is below a threshold. Merely by way of example, a direction being substantially parallel to an axis (or another direction) indicates that the angle between the direction and the axis (or the other direction) is below 30°, or below 25°, or below 20°, or below 15°, or below 10°, or below 5°, etc. In some embodiments, the direction of the magnetic field B may have an angle (e.g., 10°, 15°, 30°) with the filament axis direction A. 
       FIG.  11    is an enlarged view of a cross-sectional region  1010  of the double helix filament  1000  shown in  FIG.  10 B  according to some embodiments of the present disclosure. As illustrated in  FIG.  11   , the double helix filament  1000  may include a first filament  1111  and a second filament  1112 . In some embodiments, the first filament  1111  and the second filament  1112  may be arranged side by side. For example, the first filament  1111  and the second filament  1112  may be arranged side by side along a radial direction of the double helix filament in which the first filament  1111  may be arranged on an inner side (or outer side) of the second filament  1112  along the radial direction of the double helix filament. 
     When the first filament  1111  and the second filament  1112  are powered by a power source (not shown in  FIGS.  10 A,  10 B, and  11   ), a first direction of a first current flow of the first filament  1111  may be opposite to a second direction of a second current flow of the second filament  1112 , such that a first force (e.g., a first ampere force) on the first filament  1111  due to the magnetic field B is in line with and in an opposite direction to a second force (e.g., a second ampere force) on the second filament  1112  due to the magnetic field B. For example, as illustrated in  FIG.  11   , “x” refers to that the first direction of the first current flow of the first filament  1111  is perpendicular to the paper surface inward, and “•” refers to that the second direction of the second current flow of the second filament  1112  is perpendicular to the paper surface outward. The first force F1 on the first filament  1111  due to the magnetic field B may be in line with and in an opposite direction to the second direction of the second force F2 on the second filament  1112  due to the magnetic field B. For example, the first direction of the first force F1 on the first filament  1111  may be radially outward, and the second direction of the second force F2 on the second filament  1112  may be radially inward. 
     In some embodiments, the first filament  1111  and the second filament  1112  may be two separate filaments. For example, two separate filaments may be wound along the filament axis direction to form a first helix filament (i.e., the first filament) and a second helix filament (i.e., the second filament), respectively. Accordingly, the manufacture of the double helix filament may be simple and convenient. In this situation, two ends of the first filament, and two ends of the second filament may be power by the power source, respectively, such that the first direction of the first current flow of the first filament is opposite to the second direction of the second current flow of the second filament. 
     In some embodiments, the first filament  1111  and the second filament  1112  may be formed by a single filament. That is, the first filament and the second filament may be two portions of a single filament. For example, a first portion of a filament may be wound along the filament axis direction to form the first helix filament (i.e., the first filament). Then the filament may be bent, and a second portion of the filament may be wound along a direction opposite to the filament axis direction to form the second helix filament (i.e., the second filament). In this situation, two ends of the single filament may be power by the power source, and the first direction of the first current flow of the first filament may be opposite to the second direction of the second current flow of the second filament. 
     In some embodiments, a first current value of the first current flow of the first filament  1111  and a second current value of the second current flow of the second filament  1112  may be equal. For example, if the first filament  1111  and the second filament  1112  are two separate filaments, an end of the first filament  1111  may be electrically connected to an end of the second filament  1112  such that the first current value of the first current flow of the first filament  1111  and the second current value of the second current flow of the second filament  1112  are equal, and the first direction of the first current flow of the first filament is opposite to the second direction of the second current flow of the second filament. As another example, the first filament  1111  and the second filament  1112  may be powered by a power source, respectively, such that the first current value of the first current flow of the first filament  1111  and the second current value of the second current flow of the second filament  1112  are equal, and the first direction of the first current flow of the first filament is opposite to the second direction of the second current flow of the second filament. As a further example, if the first filament  1111  and the second filament  1112  are two portions of a single filament, the single filament may be powered by a power source such that the first current value of the first current flow of the first filament  1111  and the second current value of the second current flow of the second filament  1112  are equal, and the first direction of the first current flow of the first filament  1111  is opposite to the second direction of the second current flow of the second filament  1112 . Accordingly, the strength of the first force on the first filament  1111  due to the magnetic field B may be equal to the strength of the second force on the second filament  1112  due to the magnetic field B. The first force and the second force may be (substantially) counterbalanced. 
     In some embodiments, the cathode heater may include a supporting component  1120  (also referred to as a second component illustrated in  FIGS.  4 - 9 B ). The supporting component  1120  may enclose at least a portion of the first filament  1111  or the second filament  1112 . For example, at least the portion of the first filament  1111  or the second filament  1112  may be embedded in the supporting component  1120 . The supporting component  1120  may be made of a high temperature resistant and electrically insulating material. In some embodiments, a cross section of the supporting component  1120  may be circular, elliptical, rectangular, trapezoidal, or parallelogram. In some embodiments, the supporting component  1120  may be formed as one body for achieving a high mechanical strength. The high-strength support element may facilitate to prolong the cathode’s service life and improve its use reliability. The supporting component  1120  may protect and support the first filament  1111  and the second filament  1112 , and improve the structural stability of the cathode heater. For example, the first filament  1111  and the second filament  1112  may be embedded in the supporting component  1120 , respectively, such that the first filament  1111  and the second filament  1112  are separated by supporting component  1120 . The interference between the first filament  1111  and the second filament  1112  may be reduced or avoided, and the operation stability of the cathode heater may be improved. More descriptions of the supporting component  1120  may be found elsewhere in the present disclosure (e.g.,  FIGS.  4 - 9 B , and descriptions thereof). 
     Conventionally, the cathode heater may be a single helix filament. When the single helix filament is powered on, a current in the single helix filament may be a one-way current, for example, the current flowing from an end of the single helix filament to the other end of the single helix filament. When the single helix filament is disposed in the magnetic field B. The direction of the magnetic field B may be parallel to a filament axis direction of the single helix filament. The direction of the force on the single helix filament due to the magnetic field B may be radially inward (or radially outward), which may cause the single helix filament to shrink (or expand). When the power in the single helix filament is turned off, the shrunk (or expanded) single helix filament may restore once the force disappears. Since the single helix filament is frequently shrunk (or expanded) and restores, such deformation of the single helix filament may cause damage to the single helix filament or a supporting component, and accordingly reduce the service life of the single helix filament, and the service life of the cathode. 
     According to some embodiments of the present disclosure, the cathode heater may include at least one filament in a double helix configuration. Compared with a filament in a cylindrical configuration, by using the filament in a helix configuration (e.g., a double helix configuration), the heating power of the cathode heater may be improved. In addition, the double helix filament may include the first filament  1111  and the second filament  1112 . When the first filament  1111  and the second filament  1112  are powered by a power source, the first direction of the first current flow of the first filament  1111  may be opposite to the second direction of the second current flow of the second filament  1112 , such that the first force on the first filament  1111  due to the magnetic field B is in line with and in an opposite direction to a second force on the second filament  1112  due to the magnetic field B. Accordingly, the first force on the first filament and the second force on the second filament may be (substantially) counterbalanced, which may reduce or avoid the deformation and/or prolong the service life of the cathode heater. 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the double helix filament  1000  may also be disposed in one or more other magnetic fields. The strengths and the directions of the one or more other magnetic fields may be the same as, or different from, the strength and the direction of the magnetic field B. For example, the magnetic field B may be a component of a total magnetic field. 
     In some embodiments, a first length of the first filament  1111  may be the same as or different from a second length of the second filament  1112 . In some embodiments, a first cross-sectional area of the first filament  1111  may be the same as or different from a second cross-sectional area of the second filament  1112 . For example, if the first filament  1111  and the second filament  1112  are two separate filaments, the first cross-sectional area of the first filament  1111  is the same as the second cross-sectional area of the second filament  1112 , and the first length of the first filament  1111  are greater than the second length of the second filament  1112 , the voltage applied to the first filament  1111  may be different from the voltage applied to the second filament  1112  such that the first current value of the first current flow of the first filament  1111  and the second current value of the second current flow of the second filament  1112  are equal. 
       FIG.  12 A  is a schematic diagram illustrating an exemplary cathode heater according to some embodiments of the present disclosure.  FIG.  12 B  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure. 
     As illustrated in  FIGS.  12 A, and  12 B , a cathode heater  1200  may include a plurality of filaments  1210 . Each filament of the plurality of filaments  1210  may be of a columnar configuration (e.g., a cylindrical configuration). The plurality of filaments  1210  may be arranged in a cage configuration. For example, the plurality of filaments  1210  may be arranged along a circumferential direction of the cathode heater. An interval between adjacent filaments  1210  may be the same or different. In some embodiments, an extending direction C of the each filament of the plurality of filaments  1210  may be (substantially) parallel. 
     In some embodiments, the cathode heater  1200  may be disposed in a magnetic field B. In some embodiments, the magnetic field B may be generated by a microwave source as described in  FIG.  3   . A direction of the magnetic field B may be (substantially) parallel to the extending direction C of the each filament of the plurality of filaments  1210 . When the plurality of filaments  1210  are powered by a power source, a direction of a current flow of the each filament  1210  may be the same or opposite. The direction of the current flow of the each filament  1210  may be (substantially) parallel to the direction of the magnetic field B such that the each filament  1210  is not subjected to a force (e.g., an electromagnetic force) due to the magnetic field B, which may reduce or avoid the deformation of the filament  1210  by the force. The service life of the cathode heater  1200  may be prolonged. 
     In some embodiments, a cross section of the each filament  1210  may be circular, elliptical, rectangular, trapezoidal, parallelogram, or the like. The cross section of the each filament  1210  may be the same or different. For example, the shape and the area of the cross section of the each filament  1210  may be the same. When a same voltage is applied to the each filament  1210 , the current flow of the each filament  1210  may be the same. 
     In some embodiments, the cathode heater  1200  may include any number (or count) of filaments  1210 . For example, the cathode heater  1200  may include two, six, eight, nine, etc., filaments  1210 . The number (or count) of the filaments  1210  may be determined based on actual needs (e.g., desired heating power, a size limitation of the cathode heater, cost of the cathode heater). For example, if the desired heating power of the cathode heater  1200  is relatively high, the number (or count) of the filaments  1210  may need to be large. If the cost of the cathode heater  1200  needs to be reduced, the number (or count) of the filaments  1210  may be reduced. 
     In some embodiments, as illustrated in  FIG.  12 A , the cathode heater  1200  may include a first connection member  1220  and a second connection member  1230 . The first connection member  1220  may be operably connected to a first end of the cathode heater  1200 . The second connection member  1230  may be operably connected to a second end of the cathode heater  1200 . The cathode heater  1200  may be powered by a power source via the first connection member  1220  and the second connection member  1230 . For example, an end of each filament  1210  may be operably connected to the first connection member  1220 , and the other end of the filament  1210  may be operably connected to the second connection member  1230 . Each filament  1210  may be powered by the power source via the two ends operably connected to the first connection member  1220  and the second connection member  1230 , respectively. As another example, the plurality of filament  1210  may include a first filament, a second filament,....., and a nth filament. An end of the first filament may be operably connected to the first connection member  1220 , the other end of the first filament may be operably connected to an end of the second filament, the other end of the second filament may be operably connected to an end of a third filament, and so on, an end of the (n-1)th filament may be operably connected to an end of the nth filament, the other end of the nth filament may be operably connected to the second connection member  1230 . That is, the plurality of filament  1210  may be connected in series. In addition, the first connection member  1220  and the second connection member  1230  may provide mechanical support for the plurality of filaments  1210 , thereby improving the structural stability of the cathode heater  1200 . 
     In some embodiments, the cathode heater  1200  may include a supporting component (not shown in  FIGS.  12 A- 12 B ) (also referred to as a second component illustrated in  FIG.  4 - 9 B ). The supporting component may enclose at least a portion of the plurality of filaments  1210 . For example, the at least a portion of the plurality of filaments  1210  may be embedded in the supporting component. The supporting component may be made of a high temperature resistant and electrically insulating material. More descriptions of the supporting component may be found elsewhere in the present disclosure (e.g.,  FIG.  4 - 9 B , and descriptions thereof). 
     The supporting component may be configured based on actual needs (e.g., structural stability requirements of the cathode heater  1200 ). For example, if the cross-sectional area of the filament  1210  is relatively large, and/or the structural stability of the cathode heater  1200  is relatively good, the supporting component may not be provided. If the cross-sectional area of the filament  1210  is relatively small, and the structural stability of the cathode heater  1200  is relatively poor, the supporting component may be provided to improve the structural stability of the cathode heater  1200 . 
     According to some embodiments of the present disclosure, the cathode heater  1200  may include a plurality of filaments  1210 . Each filament of the plurality of filaments  1210  may be of a cylindrical configuration. When the plurality of filaments  1210  are powered by a power source, the direction of the current flow in each filament of the plurality of filaments  1210  may be (substantially) parallel to the direction of the magnetic field B such that the each filament  1210  is not subjected to a force, which may reduce or avoid the deformation of the filament. The service life of the cathode heater  1200  may be prolonged. In addition, by adjusting the number (or count) of the plurality of filaments  1210 , the heating power of the cathode heater  1200  may be adjusted. Furthermore, the plurality of filaments  1210  may be arranged in a cage configuration, which may improve the structural stability of the cathode heater  1200 . 
       FIG.  13 A  is a top view of an exemplary cathode heater according to some embodiments of the present disclosure. As illustrated in  FIG.  13 A , a cathode heater  1300  may include a ring-shaped filament. The structural stability and the heating power of the ring-shaped filament may be relatively high. 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the plurality of filaments  1210  may be arranged in an array of various shapes, such as an array of the shape of a ring, a circle, a square (e.g., an array  1310  illustrated in  FIG.  13 B ), or a triangle (e.g., an array  1320  illustrated in  FIG.  13 C ). 
       FIG.  14    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure. 
     As illustrated in  FIG.  14   , a thermionic emitter  1400  may include a substrate component  1410  and an electron emission layer  1420 . A cathode heater (e.g., the cathode heater  411  illustrated in  FIG.  4   , the cathode heater  511  illustrated in  FIG.  5   , the cathode heater  711  illustrated in  FIGS.  6 - 7   , the cathode heater  811  illustrated in  FIGS.  8 A- 9 B , the double helix filament  1000  illustrated in  FIG.  10   , the cathode heater  1200  illustrated in  FIGS.  12 A and  12 B ) may be disposed inside the substrate component  1410 . The substrate component  1410  may be configured to support the electron emission layer  1420 . In some embodiments, the substrate component  1410  may be of a cylindrical configuration. The substrate component  1410  may be made of molybdenum, tungsten, molybdenum, rhenium, iridium, or the like, or any combination thereof. The electron emission layer  1420  may be configured to release electrons when the electron emission layer  1420  is heated by the cathode heater. The electron emission layer  1420  may be disposed on an outer wall of the substrate component  1410 . For example, thermionic emission materials may be coated on the outer wall of the substrate component  1410  to form the electron emission layer  1420 . 
     In some embodiments, the electron emission layer  1420  may include at least one discontinuity. As used herein, a discontinuity refers to an interruption in physical characteristics or structure of an object (e.g., the electron emission layer  1420 ). For example, the electron emission layer  1420  may include the at least one discontinuity such that the electron emission layer  1420  is divided into portions. 
     In some embodiments, the electron emission layer  1420  may include at least one groove  1430  configured to cause the at least one discontinuity in the electron emission layer  1420 . In some embodiments, the at least one groove  1430  may extend along an axial direction (e.g., an axial direction D illustrated in  FIG.  14   ), a circumferential direction, and/or other direction of the substrate component  1410 . For example, as illustrated in  FIG.  14   , a plurality of grooves  1430  may extend along the axial direction D of the substrate component  1410 . In some embodiments, at least a portion of the plurality of grooves  1430  may extend in a parallel direction and be equispaced. As used herein, “a plurality of grooves being equispaced” refers to that the plurality of grooves are spaced apart by equal distances. 
     In some embodiments, the thermionic emitter  1400  may include at least one first groove (e.g., a first groove  1430 - 1  illustrated in  FIGS.  15 - 16   ) and at least one second groove (e.g., a second groove  1430 - 2  illustrated in  FIGS.  15 - 16   ). A first extending direction of the at least one first groove may be different from a second extending direction of the at least one second groove. More descriptions of the first groove and the second groove may be found elsewhere in the present disclosure (e.g.,  FIGS.  15 - 16   , and the descriptions thereof). 
     In some embodiments, a longitudinal section of the at least one groove  1430  may be rectangular, trapezoidal, parallelogram, or the like. As used herein, a longitudinal section of a groove refers to a section along an extending direction of the groove. In some embodiments, a cross section of the at least one groove  1430  may be rectangular, trapezoidal, parallelogram, or the like, as illustrated in  FIGS.  17 A- 17 C . As used herein, a cross section of a groove refers to a section along a direction perpendicular to the extending direction of the groove. 
     In some embodiments, a depth and/or a length of at least two of the at least one groove  1430  may be the same or different. As used herein, “a depth of a groove” refers to its length along a radial direction of the substrate component  1410 , e.g., the depth d illustrated in  FIG.  14   . For example, the depth of the groove  1430  may be a distance between an outer surface (e.g., a surface  1720  illustrated in  FIGS.   17 A- 17 C ) of the electron emission layer  1420  and an outer surface of the groove  1430  (e.g., a surface  1730  illustrated in  FIGS.  17 A- 17 C ) along a radial direction of the substrate component  1410 . As used herein, “a length of a groove” refers to its shortest length between a start point and an end point of the groove along an extending direction of the groove, e.g., the length L illustrated in  FIG.  14   . As used herein, an “outer surface” of the electron emission layer  1420  refers to a surface of the electron emission layer  1420  that is exposed to air or away from the substrate component  1410 , compared with the inner surface of the electron emission layer  1420 . As used herein, an “inner surface” of the electron emission layer  1420  refers to a surface of the electron emission layer  1420  that is not exposed to air or in contact with the substrate component  1410 . 
     In some embodiments, the depth of the at least one groove  1430  may be less than or equal to a thickness of the electron emission layer  1420 . As used herein, “a thickness of an electron emission layer” refer to the distance between an outer surface of the electron emission layer and an inner surface of the electron emission layer. In some embodiments, when the at least one groove  1430  extends along the axial direction of the substrate component  1410 , and the at least one groove  1430  has a straight-line shape, the length of the at least one groove  1430  may be less than or equal to a length of the electron emission layer  1420 . For example, as illustrated in  FIG.  14   , the length of each groove of the plurality of grooves  1430  may be equal to the length of the electron emission layer  1420  along the axial direction, and the depth of the each groove of the plurality of grooves  1430  may be equal to the thickness of the electron emission layer  1420  such that the plurality of grooves  1430  may penetrate through the electron emission layer  1420 . 
     In some embodiments, the electron emission layer  1420  may include any number (or count) of grooves  1430 . For example, the electron emission layer  1420  may include two grooves  1430  that are parallel to each other and extending through the entire length of the electron emission layer  1420 . The two grooves  1430  may evenly divide the electron emission layer  1420  into two portions. Accordingly, when the thermionic emitter  1400  is heated by the cathode heater, each portion of the electron emission layer  1420  may be deformed (e.g., expanded) (substantially) uniformly, thereby avoiding uneven deformation of the electron emission layer  1420 . The number (or count) of the grooves  1430  and the positions of the grooves  1430  may be determined based on actual needs (e.g., a desired performance of the thermionic emitter  1400 ). That is, the number (or count) of divided portions and/or shapes of the divided portions of the electron emission layer  1420  may be determined based on actual needs. For example, if the electron emission layer  1420  is expected to undergo relatively large thermal expansion and contraction, the number (or count) of the grooves  1430  may need to be increased. 
     During the use of the thermionic emitter  1400 , when the electron emission layer  1420  is heated by the cathode heater, and the temperature of the electron emission layer  1420  increases, the electron emission layer  1420  may have a tendency to expand. When the cathode heater is powered off, and the temperature of the electron emission layer  1420  decreases, the expanded electron emission layer  1420  may have a tendency to shrink. The electron emission layer  1420  may be squeezed or stretched due to thermal expansion and contraction, and a crack may be generated. According to some embodiments of the present disclosure, the electron emission layer  1420  disposed on the outer wall of the substrate component  1410  may include at least one discontinuity (e.g., at least one groove). The at least one discontinuity may provide a space for accommodating a deformation of the electron emission layer  1420  due to thermal expansion and contraction. The ability of the electron emission layer  1420  to accommodate the deformation due to thermal expansion and contraction may be improved. The surface stress caused by the thermal expansion or an uneven surface temperature distribution of the electron emission layer  1420  may be dispersed by the at least one discontinuity. The risk of cracking of the electron emission layer  1420  may be reduced, and the electron emission efficiency of the thermionic emitter  1400  may be improved. The service life of the thermionic emitter  1400  may be prolonged. 
     In some embodiments, the thermionic emitter  1400  may include a filling layer (not shown in  FIG.  14   ) disposed in the at least one groove  1430 . In some embodiments, the filling layer may be configured to adjust the performance of the thermionic emitter  1400 . For example, the filling layer may reduce the volatilization rate of the material of the electron emission layer  1420 . As another example, the filling layer may adjust a temperature distribution of the electron emission layer  1420 . In some embodiments, the material of the filling layer may be selected according to actual needs of the thermionic emitter  1400  to improve the performance of the thermionic emitter  1400 . For example, the filling layer may be made of a material that promotes electron emission, such as iridium. As another example, the filling layer may be made of a material that inhibits electron emission, such as hafnium. As still another example, the filling layer may be made of a volatile material. As still another example, the filling layer may be made of a ceramic material (e.g., aluminum oxide) with desirable heat transfer and heat dissipation properties. 
       FIG.  15    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure. A thermionic emitter  1500  may be similar to the thermionic emitter  1400 , except for certain features as described below. 
     As illustrated in  FIG.  15   , the thermionic emitter  1500  may include the substrate component  1410  and the electron emission layer  1420 . The electron emission layer  1420  may include a plurality of first groove  1430 - 1  and a plurality of second groove  1430 - 2 . The plurality of first grooves  1430 - 1  may extend along the circumferential direction of the substrate component  1410 , and the plurality of second grooves  1430 - 2  may extend along the axial direction (e.g., an axial direction D illustrated in  FIG.  15   ) of the substrate component  1410 . The plurality of first grooves  1430 - 1  may extend in a parallel direction and be equispaced. The plurality of second grooves  1430 - 2  may extend in a parallel direction and be equispaced. The electron emission layer  1420  may be divided into a plurality of square grids or rectangular grids. 
       FIG.  16    is a schematic diagram illustrating an exemplary thermionic emitter according to some embodiments of the present disclosure. A thermionic emitter  1600  may be similar to the thermionic emitter  1500 , except for certain features. 
     As illustrated in  FIG.  16   , the thermionic emitter  1600  may include the substrate component  1410  and the electron emission layer  1420 . The electron emission layer  1420  may include a plurality of first groove  1430 - 1  and a plurality of second groove  1430 - 2 . The plurality of first grooves  1430 - 1  may extend along a first direction of the substrate component  1410 , and the plurality of second grooves  1430 - 2  may extend along a second direction of the substrate component  1410 . The first direction and the axial direction of the substrate component  1410  may form a first angle A. The second direction and the axial direction of the substrate component  1410  may form a second angle B. The first angle A may be different from the second angle B. The first angle A and the second angle B may be greater than 0  and less than 180 . In some embodiments, an angle C between the first direction and the second direction may be an acute angle (e.g., 30 , 60 ), an obtuse angle (e.g., 120 , 150 ), or a right angle (e.g., 90  as illustrated in  FIG.  15   ). 
     It should be noted that the above descriptions merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the at least one groove  1430  may have any shape. For example, the at least one groove  1430  may have a straight-line shape, a curved line shape, a polyline shape (e.g., an “L” shape, a “Z” shape), or the like. In some embodiments, the at least one groove  1430  may be arranged continuously or intermittently along its extending direction. 
       FIGS.  17 A- 17 C  are schematic diagrams illustrating cross-sectional views of exemplary grooves according to some embodiments of the present disclosure. 
     As illustrated in  FIGS.  17 A- 17 C , a cross section of the groove  1430  may be rectangular, trapezoidal, or parallelogram. The groove  1430  may include a side surface  1710 . The side surface  1710  and an outer surface  1720  of the electron emission layer  1420  may be arranged at an angle C, such that the side surface  1710  of the groove  1430  and the outer surface  1720  of the electron emission layer  1420  form an angular boundary (rather than a rounded boundary). The angle C may be greater than 0  and less than 180 . For example, the angle C may be greater than 0 , and less than or equal to 90 . Accordingly, a plurality of sharp edges may be formed between the side surface  1710  of the groove  1430  and the outer surface  1720  of the electron emission layer  1420 . Since an electric field strength of the sharp edge is relatively strong, and electrons are easily emitted from the plurality of sharp edges than from the remaining portions of the electron emission layer  1420 , the emission efficiency of a thermionic emitter (e.g., the thermionic emitter  1400 , the thermionic emitter  1500 , the thermionic emitter  1600 ) may be improved compared to without the sharp edges (or grooves  1430 ). The temperature required for the electron emission layer  1420  to emit electrons may be reduced, and the service life of the thermionic emitter may be prolonged. 
     It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. 
       FIG.  18    illustrates a cross-sectional view of an exemplary microwave source according to some embodiments of the present disclosure. Merely for illustration, microwave source  1800  illustrated in  FIG.  18    may be a magnetron. The magnetron may be a tunable magnetron. The microwave source  1800  may include an anode block  1802 , a cathode  1804  centered in the anode block  1802 , a tuning element  1806 , a microwave transmitter  1808 , and a transmission waveguide  1810 . As described in connection with  FIGS.  3 A and  3 B , the anode block  1802  may include a plurality of resonant cavities 1802a. The resonant cavities 1802a may exist in the form of the hole-and-slot type illustrated in  FIG.  3 B . The cathode  1804  may be removably positioned in the center of the anode block. As described in connection with  FIG.  4 - 17 C , the cathode  1804  may include a cathode heater, and a thermionic emitter. More descriptions regarding the cathode may be found elsewhere in the present disclosure (e.g.,  FIG.  4 - 17 C , and the descriptions thereof). 
     The tuning element  1806  may be configured to adjust a resonant frequency of the microwave source  1800 . The resonant frequency may be changed by varying the inductance or capacitance of the resonant cavities of the microwave source. In some embodiments, the tuning element  1806  may be inserted into the hole portion of the hole-and-slot cavities. The tuning element  1806  may change the capacitance of the resonant cavities by altering the ratio of surface areas to cavity volume in a high-current region. The resonant frequency of the microwave source  1800  may be adjusted higher or lower through an insertion or removement of the tuning element  1806 . For example, when the tuning element  1806  is inserted into the anode hole, the capacitance of the cavity can be increased, thereby the resonant frequency may be decreased. In some embodiments, the microwave source  1800  may include multiple tuning elements  1806  operably connected to each resonant cavity 1802a. Merely for illustrative purposes, just one tuning element  1806  is illustrated. In some embodiments, the tuning element  1806  may be made of an electrically conductive material (e.g., copper, aluminum, or other metal materials). 
     The microwave transmitter  1808  may be configured to transmit the microwaves generated by the microwave source  1800 . The microwaves may be transmitted into the transmission waveguide  1810  (e.g., the transmission waveguide illustrated in  FIG.  2   ). Then transmission waveguide  1810  may transmit the microwaves to an accelerator tube (e.g., the accelerator tube  210 ) in order to provide the kinetic energy to accelerate electrons in the accelerator tube. 
       FIG.  19    illustrates a cross-sectional view of an exemplary microwave source according to some embodiments of the present disclosure. As illustrated in  FIG.  19   , microwave source  1900  may be a multi-cathode microwave source (e.g., a multi-cathode magnetron). The microwave source  1900  may include an anode block  1902  and multiple cathodes, such as a first cathode  1904  and a second cathode  1906 . In some embodiments, the multiple cathodes may be removably positioned in the center of the anode block  1902 . In some embodiments, when an individual cathode (e.g., the first cathode  1904  or the second cathode  1906 ) of the multiple cathodes is removably positioned in the center of the anode block, microwaves having a specific frequency (e.g., a specific microwave power) are generated in response to an occurrence of a resonance effect caused by the anode block and the cathode. More descriptions regarding the anode block and the cathode may be found elsewhere in the present disclosure (e.g.,  FIGS.  3 A- 17 C , and the descriptions thereof). 
     In some embodiments, respective diameters of the multiple cathodes may be different. In some embodiments, the diameters of at least two of the multiple cathodes may be different. For example, the first cathode diameter may be 18 mm and the second cathode diameter may be 22 mm. In some embodiments, the microwave source  1900  may include a connector  1908 . The multiple cathodes may be mechanically connected to each other by the connector  1908 . The connector  1908  (e.g., a support rod) may be configured to support and connect each cathode. The connector  1908  may be made of an insulative material. In some embodiments, the microwave source  1900  may include a limiting member  1910 . An end of the connector  1908  may be operably connected to the limiting member  1910 . In some embodiments, the microwave source  1900  may include a guide slot  1912 . The limiting member  1910  may be disposed in the guide slot  1912 . In some embodiments, the limiting member  1910  may move (e.g., slide) along the guide slot  1912  in order to position the cathode of the multiple cathodes. For example, when the limiting member  1910  is moved to a first location, the first cathode  1904  can be positioned in the center of the anode block  1902 . When the limiting member  1910  is moved to a second location, the second cathode  1906  can be positioned in the center of the anode block  1902  and the first cathode  1904  may be moved out. In some embodiments, the limiting member  1910  may be driven by various driving devices. Exemplary driving devices may include a hydraulic driver, a pneumatic driver, an electric actuator. In some embodiments, the various driving devices may not cause interferences for the generation of microwaves. 
     An electronic efficiency of the microwave source (e.g., the magnetron) may rely on a ratio of diameters of the cathode and the anode block (also referred to as “diameter ratio”). When the dimeter ratio is in a specific range, the electron efficiency may be at an optimal value, and an output power of the microwave source may be maximum. For example, for an eight-cavities anode block, when the diameter ratio is in the rage of 0.37-0.42, the electronic efficiency of the magnetron may be optimal. As another example, for a twelve-cavities anode block, when the diameter ratio is in the range of 0.50-0.58, the electronic efficiency of the magnetron may be optimal. As a further example, for a sixteen-cavities anode block, when the diameter ratio is in the range of 0.60-0.66, the electronic efficiency of the magnetron may be optimal. 
     In some embodiments, the output power of the microwave source can be changed by varying the diameter ratio of the anode block to the cathode. In some embodiments, for a specific anode block, the diameter ratio can be changed by alternating the cathodes having different diameters. Merely for illustration, for a magnetron including a twelve-cavities anode block, its resonant frequency is 2998 MHz and maximum output power is 3.4 MW. Given that the diameter of the anode block is 34 mm. The maximum output power of the magnetron can be reached only if the diameter of the cathode in the range of 17-19.72 mm. It is understood that, when the diameter of a cathode is less than 17 mm or greater than 19.72 mm, the magnetron may output a relatively small microwave power. By arranging the constant anode block and one of the cathodes having different diameters, the magnetron may output alternative microwave powers. The alternative microwave powers may be used to generate radiation beams of different energies. For example, the diameter of the anode block  1902  is set as 34 mm and the diameter of the first cathode  1904  is set as 18 mm. When the anode block  1902  and the first cathode  1904  are powered on, the microwave source  1900  may output the maximum microwave power for accelerating electrons in the accelerator tube  210  to generate therapeutic radiation beams. The therapeutic radiation beams may be applied to the subject for eliminating tumor tissues. As another example, the diameter of the second cathode  1906  is set as 22 mm. When the anode block  1902  and the second cathode  1906  are powered on, the microwave source  1900  may output a relatively small microwave power for accelerating electrons in the accelerator tube  210  to generate imaging radiation beams. For the IGRT device, the imaging radiation beams may be used to image a region of interest (ROI) related to the subject. The radiotherapy procedure may be guided according to the ROI related information (e.g., a tumor region). 
     In some embodiments, the resonant frequency of the microwave source can be changed by alternating different cathodes. The resonant frequency of the microwave source may rely on an equivalent capacitance and inductance of the microwave source. For example, the resonant frequency, 
     
       
         
           
             f 
             = 
             
               1 
               
                 
                   
                     L 
                     C 
                   
                 
               
             
             , 
           
         
       
     
     where L denotes the inductance and C denotes the equivalent capacitance. For the constant anode block, the larger the diameter of the cathode, the smaller the distance between the cathode and the anode block, thereby the equivalent capacitance becomes larger. The resonant frequency may be changed with the equivalent capacitance. In some embodiments, by switching cathodes of different diameters, different resonant frequency may be produced accordingly. In addition, the tuning element (e.g., the tuning element  1806 ) of the microwave source may slightly adjust the resonant frequency, such as ±5 MHz. The adjustable range of the resonant frequency of the microwave source may be enlarged due to the use of the multiple cathodes and the tuning element. It is understood that the frequencies of output microwaves may be changed by varying the characteristics (e.g., resonant frequencies) of the microwave source. Specific microwave frequencies may be produced when different cathodes are applied. 
     Various embodiments are provided herein with reference to a microwave source composed of an anode block and one or more cathodes. In some embodiments, the microwave source (e.g., a single-cathode microwave source) may include an anode block and a cathode centered in the anode block. In some embodiments, the microwave source (e.g., a multi-cathode microwave source) may include an anode block and multiple cathodes. The multiple cathodes may share the same anode block. In some embodiments, one of the multiple cathodes can be removably positioned in the anode block. Diameters of the multiple cathodes may be different. In response to an occurrence of a resonance effect caused by the anode block and the cathode positioned in the anode block, microwaves having a specific frequency may be generated. For example, when a first cathode is positioned in the anode block, first microwaves having a first frequency may be generated due to the resonant effect caused by the anode block and the first cathode. As another example, when a second cathode is positioned in the anode block, second microwaves having a second frequency may be generated due to the resonant effect caused by the anode block and the second cathode. The first frequency and the second frequency may be different. Different microwave powers can be output. Compared with a single-cathode microwave source, a multi-cathode microwave source may output alternative microwave powers and/or frequencies by grouping the anode block and a cathode of the multiple cathodes. 
     Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure, and are within the spirit and scope of the exemplary embodiments of this disclosure. 
     Moreover, certain terminology has been used to describe embodiments of the present disclosure. For example, the terms “one embodiment,” “an embodiment,” and “some embodiments” mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the present disclosure. 
     Further, it will be appreciated by one skilled in the art, aspects of the present disclosure may be illustrated and described herein in any of a number of patentable classes or context including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a “module,” “unit,” “component,” “device,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electro-magnetic, optical, or the like, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, RF, or the like, or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET, Python or the like, conventional procedural programming languages, such as the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL 2002, PHP, ABAP, dynamic programming languages such as Python, Ruby and Groovy, or other programming languages. The program code may execute entirely on the user’s computer, partly on the user’s computer, as a stand-alone software package, partly on the user’s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user’s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS). 
     Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose, and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software only solution, e.g., an installation on an existing server or mobile device. 
     Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, claim subject matter lie in less than all features of a single foregoing disclosed embodiment.