Electromagnetic radiation generation

Abstract

In one embodiment, an apparatus (100) is described. The apparatus includes an electron source (104) configured to generate electromagnetic radiation (102) including frequency components in a frequency range of 10 GHz to 10 THz and configured to produce an electron beam (106). The apparatus further includes a magnetic field generator (108) configured to generate a magnetic field that conditions and guides the electron beam within an interaction region where the electromagnetic radiation (102) is generated. The apparatus further includes a waveguide (110) comprising a cylindrical structure. The cylindrical structure is aligned coaxially with the electron beam in the interaction region. An inner surface (216) of the cylindrical structure is configured to facilitate Cerenkov interaction between the electron beam and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation. The apparatus further includes an output coupler (112) configured to output the electromagnetic radiation from the apparatus. The apparatus further includes an electron beam collector (114) configured to collect the electron beam and recover energy from the electron beam after the interaction region.

Description

[Technical Field]

[0001] The present invention particularly relates to generating electromagnetic radiation for use in high power applications such as, but not limited to, plasma heating in nuclear fusion reaction systems, remote environmental monitoring, and quality assessment of large area composite materials. [Background technology]

[0002] Gyrotrons provide continuous wave (CW) sources of electromagnetic (EM) radiation for use in high-power applications such as plasma heating in nuclear fusion reaction systems. Such gyrotrons may be capable of delivering output powers between 0.5 MW and 2 MW in the frequency range between 70 GHz and 300 GHz (where higher power correlates with lower frequency). Gyrotrons have experimentally exhibited efficiencies of up to 50% at lower frequencies. Other sources of EM radiation, such as backward wave oscillators (BWOs) and traveling wave tubes (TWTs), may be able to achieve efficiencies greater than 70%. However, the output power of a BWO or TWT cannot exceed 1 kW, which is not sufficient for high-power applications.

[0003] To reach higher efficiencies, a multistage voltage-decreasing collector (MDC) can be used to recover energy from the system. Gyrotrons are not known to achieve efficiencies greater than 55% due to the need to extract energy from the circular motion of the helical electron beam (i.e., the electron beam spiral trajectory). The circular motion of the helical electron beam is used to support the electron beam's interaction with the transverse electric (TE) modes of the gyrotron cavity, i.e., the EM wave. To achieve high efficiency (approximately 30%–40%) in microwave generation, the electron beam in high-power gyrotrons has more than 50% of its energy in the circular motion, which limits the ability of the energy recovery stage to further improve efficiency beyond 55%. BWO / TWTs are driven by a laminar electron beam with 90% of the beam's energy in the translational motion, which allows for efficient extraction of energy (up to 80%) from the beam used to generate microwave radiation using an MDC. To suppress the excitation of parasitic modes, BWO / TWTs cannot reach MW powers (necessary for nuclear fusion) because the lateral dimensions (e.g., diameter) of the interaction region are on the order of the interaction wavelength, thus limiting the power that the source can generate. Increasing the diameter of the interaction region is expected to end the stable steady-state single-mode operation of the radiation source. Summary of the Invention [Problem to be solved by the invention]

[0004] As noted above, existing technologies for generating EM radiation for use in high-power applications such as plasma heating in nuclear fusion reactor systems and other high-power applications have limitations. Therefore, improvements aimed at addressing these limitations would be beneficial. [Means for solving the problem]

[0005] Thus, according to a first aspect of the present disclosure, there is provided an apparatus configured to generate electromagnetic radiation including frequency components in a frequency range of 10 GHz to 10 THz. The apparatus includes an electron source configured to generate an electron beam. The apparatus further includes a magnetic field generator configured to generate a magnetic field that conditions and guides the electron beam within an interaction region where the electromagnetic radiation is generated. The apparatus further includes a waveguide having a cylindrical structure. The cylindrical structure is aligned coaxially with the electron beam in the interaction region. The inner surface of the cylindrical structure is configured to facilitate Cerenkov interaction between the electron beam and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation. The apparatus further includes an output coupler configured to output the electromagnetic radiation from the apparatus. The apparatus further includes an electron beam collector configured to collect the electron beam and recover energy from the electron beam after the interaction region.

[0006] According to a second aspect of the present disclosure, there is provided a method for generating electromagnetic radiation containing frequency components in a frequency range from 10 GHz to 10 THz. The method includes generating an electron beam. The method further includes generating a magnetic field that conditions and guides the electron beam within an interaction region in which the electromagnetic radiation is generated. The method further includes using a waveguide comprising a cylindrical structure to facilitate Cerenkov interaction between the electron beam and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation. The cylindrical structure is aligned coaxially with the electron beam in the interaction region. The method further includes outputting the electromagnetic radiation. The method further includes collecting the electron beam after the interaction region to recover energy from the electron beam.

[0007] According to a third aspect of the present disclosure, there is provided a nuclear fusion reaction system comprising a chamber configured to confine a plasma, and further comprising an apparatus according to the first aspect or any related embodiment, wherein electromagnetic radiation output by the apparatus is configured to heat the plasma.

[0008] According to a fourth aspect of the present disclosure, a waveguide for a device configured to generate electromagnetic radiation containing frequency components in a frequency range of 10 GHz to 10 THz is provided. The waveguide comprises a cylindrical structure. The inner surface of the cylindrical structure is configured to facilitate Cherenkov interaction between an electron beam generated by the device and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation. The cylindrical structure is aligned coaxially with the electron beam in an interaction region of a magnetic field for conditioning and guiding the electron beam, where the electromagnetic radiation is generated. The diameter D of the cylindrical structure satisfies the condition D / λ>3, where λ is the wavelength related to the frequency components.

[0009] In accordance with the aspects described above and the embodiments described below, limitations of existing technology are addressed. Specifically, more efficient generation (e.g., but not limited to, about 80%) of coherent, high-power (e.g., but not limited to, in the range of 0.5 MW to 2 MW) EM radiation is possible compared to gyrotron technology. Accordingly, improved apparatus and methods for generating EM radiation, improved waveguides for facilitating the generation of EM radiation using such apparatus, and improved nuclear fusion systems are provided.

[0010] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

[0011] Exemplary embodiments of the present invention will now be described, by way of example only, with reference to the following drawings: [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an apparatus configured to generate electromagnetic radiation, according to one embodiment. [Figure 2] FIG. 1 is a schematic diagram of a waveguide for use in a device according to one embodiment. [Figure 3] 1 is a schematic diagram of a nuclear fusion reaction system according to one embodiment. [Figure 4]FIG. 1 is a diagram of a method for generating electromagnetic radiation according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] As highlighted above, although certain technologies, such as BWO / TWT, exist for the generation of highly efficient EM radiation (e.g., in the frequency range between 70 GHz and 300 GHz), such technologies are unable to generate EM radiation with an output power suitable for high-power applications such as plasma heating in nuclear fusion reaction systems, or to operate at higher frequencies (e.g., above 300 GHz) generating sufficient output power (e.g., above 10 W). Therefore, other technologies, such as gyrotrons, have been adopted for such high-power applications.

[0014] For nuclear fusion to be commercially viable, the power output of a fusion reactor system should exceed the energy input to the system. The energy input involves heating the plasma to a temperature high enough to trigger the fusion reaction. Energy efficiency improvements that can be made in any part of a fusion reactor system, no matter how small, can contribute to creating a commercially viable fusion reactor system. At a maximum efficiency of 55%, gyrotrons are relatively inefficient at producing EM radiation compared to other technologies.

[0015] Therefore, improvements are needed.

[0016] 1 is a schematic diagram of an apparatus 100 configured to generate electromagnetic (EM) radiation 102, according to one embodiment. The generated EM radiation 102 includes frequency components in the frequency range of 10 GHz to 10 THz.

[0017] Apparatus 100 includes an electron source 104 (e.g., an electron gun) configured to produce an electron beam 106. As described in more detail herein, electron source 104 is configured to produce electron beam 106 in a manner suitable for conditioning and steering within apparatus 100. Although not specifically depicted in FIG. 1 , electron source 104 may include a set of components that facilitate producing electron beam 106. For example, electron source 104 may include an electron gun for producing electron beam 106.

[0018] The apparatus 100 further comprises a magnetic field generator 108 configured to produce a magnetic field to condition and guide the electron beam 106 within an interaction region where the EM radiation 102 is generated. One or more magnetic field generators 108 (e.g., coils) may be included as part of the apparatus 100 to achieve the conditioning and guiding functions. The electron beam 106 may need to be conditioned using the magnetic field generator 108 by compressing, shaping, and / or "cooling down" (meaning changing the beam shape in six-dimensional (velocity, spatial) parameter space, as described in more detail below). Such conditioning can prepare the electron beam for better interaction with the electromagnetic fields within the apparatus 100. As used herein, the term "guiding" refers to driving the electron beam 106.

[0019] The magnetic field generator 108 can comprise a cryogenically cooled electromagnetic system or an uncooled magnet system, such as may be implemented by a gyrotron. The function of the magnetic field generated by the magnetic field generator 108 may differ from that of the magnetic field generated in a gyrotron. For example, in a gyrotron, the magnetic field functions to drive the spiral electron beam and adjust the operating mode and frequency of the gyrotron. In the apparatus 100, the magnetic field functions to drive the electron beam 106 and facilitate interaction between the electron beam 106 and other components of the apparatus 100, as described in more detail below.

[0020] As used herein, the term "interaction region" refers to the section of device 100 where EM radiation 102 is generated as a result of an interaction, as described in more detail below.

[0021] The apparatus 100 further comprises a waveguide 110. The waveguide 110 comprises a cylindrical structure. The cylindrical structure is coaxially aligned with the electron beam 106 in an interaction region. The inner surface of the cylindrical structure is configured to facilitate Cerenkov interaction between the electron beam 106 and an electromagnetic field excited and supported inside the waveguide 110 to generate electromagnetic radiation 102.

[0022] The physics of the generation of EM radiation 102 by device 100 differs from that of a gyrotron. Instead of a cyclotron-type interaction in which a spiral electron beam emits EM radiation, in a gyrotron, the interaction is instead a Cherenkov interaction.

[0023] In a Cerenkov-type interaction, EM radiation 102 is produced as a result of the electron beam 106 being decelerated due to the effect of the electromagnetic fields excited and supported inside the waveguide 110. As will be discussed in more detail below, it is not necessary to use a helical electron beam when relying on a Cerenkov-type interaction; other types of electron beams can be used.

[0024] The high-Q cavity (defined by the interaction region) of the device 100 may have very sharp resonances, which may require tuning (as discussed previously) to bring the electron beam 106 into resonance, which depends specifically on the longitudinal velocity of the electron beam 106 (i.e., Cerenkov interaction). During tuning, changes to the shape and longitudinal and transverse velocities of the electron beam 106 (e.g., increasing the transverse velocity and decreasing the longitudinal velocity, or any other suitable change) may be required to tune the electron beam 106 into resonance.

[0025] As will be described in more detail below, the cylindrical structure may have an appropriate configuration to facilitate Cerenkov interactions.

[0026] The apparatus 100 further includes an output coupler 112 configured to output the electromagnetic radiation 102 from the apparatus 100. For example, the output coupler 112 may include a reflector configured to reflect at the operating wavelength of the apparatus 100. The output coupler 112, specific to a particular mode of operation, may be positioned to reflect the EM radiation 102 while also allowing the electron beam 106 to pass to a subsequent section of the apparatus 100. For example, the reflector may be annular, allowing the electron beam 106 to pass through its center and reflect the annular beam profile of the EM radiation 102. Another configuration of the reflector may be a Vlasov-type mode transformer. The design and location of the output coupler 112 may depend on various parameters, such as the beam profile of the electron beam 106, the operating mode configuration, and any other parameters that may affect the beam profile of the EM radiation 102.

[0027] The apparatus 100 further includes an electron beam collector 114 configured to collect the electron beam 106 and recover energy from the electron beam 106 after the interaction region. For example, the electron beam collector 114 may include a reduced voltage collector, such as a multi-stage reduced voltage collector (MDC). The electron beam collector 114 may recover energy (via circuitry not shown) from the electron beam 106 after it passes through the interaction region. The amount of energy recovered from the electron beam 106 plays a role in determining the energy efficiency of the apparatus 100, as the recovered energy may be used to reduce the energy input to the apparatus 100 to generate a given amount of EM radiation 102 power.

[0028] Thus, while there are similarities between device 100 and a gyrotron, there are some differences. The EM radiation 102 generated by device 100 is based on a Cherenkov interaction with an electron beam 106 instead of a cyclotron interaction as in a gyrotron. One of the differences between device 100 and a gyrotron is the inclusion of a waveguide 110 in the interaction region.

[0029] Interest in generating EM radiation for high-power applications based on Cherenkov interactions has been limited due to the relatively low efficiencies possible with this technology. For example, using technology based on Cherenkov-type interactions can allow efficiencies of up to 20-30% at lower frequencies and up to 10% at higher frequencies. Therefore, the trend in the art has been to use other devices such as gyrotrons for high-power applications and BWOs and TWTs for low-power applications.

[0030] However, the present disclosure identifies the potential for greater than expected energy efficiency improvements through the use of such Cerenkov-type interactions.

[0031] As mentioned previously, there is a limit to the energy efficiency that can be obtained with a gyrotron (e.g., a maximum of 55%). An important reason for this limit is due to the characteristics of the electron beam in the gyrotron and the design of the electron beam collector (e.g., multi-stage voltage-reduced collector). The energy from the spiral motion of the electron beam in the gyrotron is relatively difficult to recover, which places a practical limit on the level of energy recovery possible with an MDC coupled to a gyrotron.

[0032] However, apparatus 100 does not require the same use of such a spiral electron beam due to the different type of interaction that generates EM radiation 102, which opens the possibility of using a more efficient electron beam collector. Rather, the present disclosure identifies higher energy recovery (e.g., greater than 55%, potentially greater than 60%) when employing the Cerenkov-type interaction facilitated by waveguide 110 alongside a more efficient electron beam collector that can be used when not relying on a spiral electron beam. Such a combination of waveguide 110 and electron beam collector 114 has not previously been contemplated due to the view in the art that Cerenkov-type interactions tend to result in insufficient efficiency in high power applications.

[0033] Thus, apparatus 100 and related embodiments can increase the overall efficiency of a source of EM radiation 102 in the 10 GHz to 10 THz range while making the source's operation more stable and robust. The design of apparatus 100 is such that components are supplied modularly, allowing for cheaper manufacture and servicing. Thus, apparatus 100 can help reduce manufacturing and servicing costs, increase overall efficiency to over 60%, and, as a result, reduce the amount of input energy required to sustain a fusion reaction and / or have improved reliability because apparatus 100 is less sensitive to the external environment.

[0034] Several embodiments of the device 100 are now described.

[0035] FIG. 2 is a schematic diagram of a waveguide 210 for use in an apparatus such as apparatus 100, to which reference will be made in the following description. As previously mentioned, the role of the waveguide 210 is to facilitate a Cerenkov-type interaction. In this manner, the waveguide 210 forms a cavity (i.e., a resonator) within which the generation of EM radiation 102 occurs. The electron beam 106 is decelerated by the field inside the cavity, thus generating electromagnetic radiation based on the Cerenkov principle. Due to the efficient interaction between the EM field inside the cavity and the electron beam 106, there is no need to pump the electron beam in a transverse (i.e., circular) motion, as most of the energy in the electron beam 106 is in the translational (i.e., longitudinal) direction. After interaction in the interaction region, the electron beam propagates to the electron beam collector 114, where more efficient energy recovery can occur.

[0036] FIG. 2(A) depicts the cylindrical structure of waveguide 210. To aid in describing the structural features of waveguide 210, a coordinate system is established. The longitudinal direction is referred to as the z-axis. The azimuthal direction is specified by the azimuthal coordinate φ, which defines a given radial angular measurement from the longitudinal axis of the cylindrical structure. The radius r refers to the distance from the origin / center of the cylindrical structure (defined by the longitudinal axis) to the inner surface 216 of waveguide 210. When integrated with apparatus 100, the cylindrical structure is coaxial with the propagation axis of electron beam 106 passing through the hollow portion of the cylindrical structure.

[0037] The inner surface 216 of the waveguide 210 is configured to facilitate Cerenkov-type interactions to allow for high-order mode selection with large diameters. High-order modes are modes with many radial or azimuthal variations, i.e., for example, E m,nwhere m (and / or) n is much greater than 1, i.e., m(n)>>1. By way of example, for a waveguide 210 having a mean diameter D and an operating wavelength λ that satisfies the condition D / λ>3, the number of azimuthal variations may be m≧5 and / or n≧5. Furthermore, the waveguide 210 is configured to support the interaction of the flow of electron beam 106 with the EM field excited and supported due to the design of the waveguide 210 (i.e., eigenmodes of the cavity). The waveguide 210 (cavity) can be considered a surface-field cavity because a surface EM field is induced in the waveguide 210 as a result of the interaction between the electron beam 106 and the waveguide 210, which functions to decelerate the electron beam 106 and thereby emit EM radiation 102.

[0038] The waveguide 210 can comprise a metallic (e.g., copper, silver, etc.) or composite cylindrical structure (including highly conductive materials such as metals and less conductive materials that provide support for the highly conductive materials) with periodic perturbations along both the longitudinal and azimuthal directions (along the propagating electron beam). The periodic perturbations are designed to suppress the movement of electrons inside the conductive material in certain directions, thereby increasing the impedance of the waveguide 210 compared to a cylindrical structure without such perturbations. These periodic perturbations are such that the radius r varies depending on the longitudinal and azimuthal coordinates. These periodic perturbations can restrict the free electron movement (i.e., increase the impedance) in both the longitudinal and azimuthal directions, which results in the excitation of certain cavity eigenmodes (fields) inside the waveguide 210, which act on the electron beam 106, resulting in the deceleration of the electron beam 106 and the corresponding generation of EM radiation 102.

[0039] Thus, in some embodiments, the inner surface 216 comprises a two-dimensional periodic structure configured such that the radial distance r between the longitudinal axis of the cylindrical structure and a location on the inner surface 216 varies depending on both the longitudinal and azimuthal coordinates of the location on the inner surface. A non-limiting example of such a two-dimensional periodic structure is depicted in FIG. 2(B), which depicts a checkerboard pattern on the inner surface 216. The checkerboard pattern represents a two-dimensional periodic structure. FIG. 2(C) depicts a cross-section of the two-dimensional periodic structure depicted by FIG. 2(B). In FIG. 2(C), the curvature of the cylindrical structure is not depicted. Thus, it is clear that the inner surface 216 includes a series of periodic perturbations in its two-dimensional surface structure. FIG. 2 depicts a rectangular-type periodic structure with two possible levels (e.g., heights) relative to the mean radius of the cylindrical structure.

[0040] Thus, in some embodiments, the inner surface 216 has periodic variations in surface height that vary in two dimensions along the inner surface 216 .

[0041] Other types of two-dimensional periodic structures, such as those based on sinusoidal (e.g., wave-like) structures, can be used in waveguide 210. For example, if the radius r of inner surface 216 is

number

[0042]

number

number

[0043] is the number of azimuthal variations of the two-dimensional periodic structure, and φ is the azimuthal coordinate.

[0044] In some cases, cylindrical structures can be fabricated by machining the surface of a metal plate with any two-dimensional periodic structure as described above, and then rolling the plate into a cylindrical structure with the machined surface on the inside of the cylindrical structure.

[0045] The magnitude / depth of the surface height variations / disturbances can be in the range of 0.1 to 10 times the operating wavelength of device 100, allowing electromagnetic waves to form a field inside the cylindrical structure. Thus, in some embodiments, the surface height variations have a magnitude in the range of 0.1 to 10 times the operating wavelength of device 100. The operating wavelength λ is related to the frequency component f, for example, via the equation c=fλ, where c is the speed of light.

[0046] In some embodiments, the inner surface 216 comprises a conductor, such as a metal, and is structured to increase the impedance of the waveguide 210 both longitudinally and azimuthally along the cylindrical structure. The two-dimensional periodic structures described above are examples of structures that increase the impedance of the waveguide 210.

[0047] The lateral dimensions of the cavity, such as diameter D, can be identified in terms of the operating wavelength λ, which may be in the range of 3 cm (centimeters) to 30 μm (micrometers). Diameter D may be in the range of D / λ=3...1000, which may enable maintaining low power densities to reliably support continuous wave (CW) high-power operation of device 100 in the output power range of 0.1 MW to 10 MW. Increasing the diameter of the interaction region without adding waveguide 210 may result in the termination of stable single-mode operation. Thus, the addition of waveguide 210 can help support stable single-mode operation at high power output and low power density.

[0048] Thus, in some embodiments, the diameter D of the cylindrical structure satisfies the condition D / λ>3, where λ is the operating wavelength of the device. That is, the condition is that the ratio of the diameter D to the operating wavelength λ is greater than 3. The operating wavelength is related to the frequency content. The diameter can refer to the average radius of the cylindrical structure. Such a parameter relationship of D / λ>3 has not been used before. Other parameter relationships are possible, such as D / λ>4, 4.1, ..., 5, 5.1, ..., 10, ..., 1000, etc.

[0049] In some embodiments, apparatus 100 is configured to output electromagnetic radiation 102 at an average power of 250 kW in the frequency range of 10 GHz to 300 GHz, 1 kW in the frequency range of 300 GHz to 1 THz, and / or greater than 100 W in the frequency range above 1 THz. The use of waveguide 210 as described above facilitates such high power operation in the specified frequency ranges.

[0050] In some embodiments, the device 100 is configured to output continuous wave electromagnetic radiation 102 .

[0051] In some embodiments, the device 100 is configured to output pulsed electromagnetic radiation 102 .

[0052] In some embodiments, the apparatus is for heating a plasma in a nuclear fusion reaction system. In some embodiments, the apparatus is for use in large area surveying and environmental monitoring. In some embodiments, the apparatus is for use in large area composite material quality assessment.

[0053] In some embodiments, the electron beam 106 has most of its energy in a laminar manner (eg, laminar).

[0054] While the electron beam 106 is in the interaction region, the electron beam profile may be annular, as in the case of a gyrotron. However, the majority of the electron beam's total energy is in the translational direction rather than the circular (transverse) direction. Thus, in some embodiments, the electron beam has more than 75% of its energy in laminar flow and less than 25% of its energy in circular motion. As previously mentioned, it may be easier to recover energy from a laminar electron beam than a helical electron beam. By providing more energy to the laminar portion of the electron beam, overall energy efficiency can be increased due to the greater amount of energy recovery possible from such electrons.

[0055] 3 is a schematic diagram of a fusion reaction system 320 according to one embodiment. The fusion reaction system 320 comprises a chamber 322 configured to contain a plasma (e.g., based on a tokamak-type design or any other suitable design). The fusion reaction system 320 further comprises an apparatus 300 (e.g., having the same features as apparatus 100 of FIG. 1 or any related embodiment). EM radiation output by the apparatus is configured to heat the plasma. In this regard, the apparatus 300 is operably coupled to the chamber 322 for receiving the EM radiation.

[0056]

[0023] Figure 4 refers to a method 400 for generating electromagnetic radiation according to one embodiment. The generated electromagnetic radiation includes frequency components in the frequency range of 10 GHz to 10 THz. In the following description, reference is made to Figure 1.

[0057] The method 400 includes, at block 402 , producing an electron beam 106 .

[0058] The method 400 further includes, at block 404, creating a magnetic field to guide the electron beam 106 within an interaction region where the electromagnetic radiation 102 is generated.

[0059] The method 400 further includes, at block 406, using a waveguide 110 comprising a cylindrical structure to facilitate Cerenkov interaction between the electron beam 106 and an electromagnetic field excited and supported inside the waveguide 110 to generate the electromagnetic radiation 102. The cylindrical structure is aligned coaxially with the electron beam 106 in the interaction region.

[0060] The method 400 further includes outputting electromagnetic radiation 102 at block 408 .

[0061] The method 400 further includes, at block 410, collecting the electron beam 106 after the interaction region to recover energy from the electron beam 106.

[0062] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustrations and descriptions are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

[0063] One or more features described in one embodiment may be combined with or interchanged with features described in another embodiment.

[0064] Elements or steps described with respect to one embodiment can be combined with or substituted for elements or steps described with respect to another embodiment. Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude plurals. Any reference signs in the claims should not be construed as limiting the scope. [Explanation of symbols]

[0065] 100 devices 102 Electromagnetic radiation, EM radiation 104 Electron Source 106 Electron Beam 108 Magnetic field generator 110 Waveguide 112 Output Coupler 114 Electron Beam Collector 210 Waveguide 216 Interior 300 equipment 320 Nuclear Fusion Reaction System 322 Chamber

Claims

1. 1. An apparatus (100) configured to generate electromagnetic radiation (102) comprising frequency components in the frequency range of 10 GHz to 10 THz, comprising: an electron source (104) configured to produce an electron beam (106); a magnetic field generator (108) configured to generate a magnetic field to condition and guide the electron beam within an interaction region where the electromagnetic radiation (102) is generated; a waveguide (110) comprising a cylindrical structure, the cylindrical structure being coaxially aligned with the electron beam in the interaction region, an inner surface (216) of the cylindrical structure being configured to facilitate Cerenkov interaction between the electron beam and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation; an output coupler (112) configured to output the electromagnetic radiation from the device; an electron beam collector (114) configured to collect the electron beam and recover energy from the electron beam after the interaction region; An apparatus (100) comprising:

2. 2. The apparatus of claim 1, wherein the inner surface comprises a two-dimensional periodic structure configured such that a radial distance between a longitudinal axis of the cylindrical structure and a location on the inner surface varies depending on both a longitudinal coordinate and an azimuthal coordinate of the location on the inner surface.

3. 3. The apparatus of claim 1, wherein the inner surface has periodic surface height variations that vary in two dimensions along the inner surface.

4. 4. The apparatus of claim 3, wherein the surface height variations have a magnitude in the range of 0.1 to 10 times an operating wavelength of the apparatus, the operating wavelength being related to the frequency components.

5. 5. The apparatus of claim 1, wherein the inner surface comprises a conductor, the inner surface being constructed to increase the impedance of the waveguide in both longitudinal and azimuthal directions along the cylindrical structure.

6. 6. The device according to claim 1, wherein the diameter D of the cylindrical structure satisfies the condition D / λ>3, λ being the operating wavelength of the device, and wherein the operating wavelength is related to the frequency component.

7. 250kW in the frequency range of 10GHz to 300GHz, 1 kW in the frequency range 300 GHz to 1 THz, and / or 100W in the frequency range above 1 THz, 7. The apparatus of claim 1, configured to output electromagnetic radiation at an average power greater than

8. 8. The device of any one of claims 1 to 7, configured to output continuous wave or pulsed wave electromagnetic radiation.

9. 9. Apparatus according to any one of claims 1 to 8 for heating a plasma in a nuclear fusion reaction system.

10. 10. The apparatus of claim 1, wherein the electron beam has most of its energy in a laminar flow.

11. 11. The apparatus of claim 10, wherein the electron beam has more than 75% of its energy in laminar flow and less than 25% of its energy in circular motion.

12. a chamber (322) configured to contain the plasma; A device (300) according to any one of claims 1 to 11; wherein the electromagnetic radiation output by the device is configured to heat the plasma.

13. 1. A method (400) for generating electromagnetic radiation containing frequency components in the frequency range of 10 GHz to 10 THz, comprising: Producing an electron beam (402); creating a magnetic field (404) that conditions and guides the electron beam within an interaction region where the electromagnetic radiation is generated; using a waveguide (406) comprising a cylindrical structure to facilitate Cerenkov interaction between the electron beam and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation, the cylindrical structure being aligned coaxially with the electron beam in the interaction region; outputting (408) said electromagnetic radiation; collecting (410) the electron beam after the interaction region to recover energy from the electron beam; The method (400) includes:

14. 1. A waveguide (110) for an apparatus (100) configured to generate electromagnetic radiation containing frequency components in a frequency range of 10 GHz to 10 THz, comprising: the waveguide comprises a cylindrical structure; an inner surface (216) of the cylindrical structure configured to facilitate Cerenkov interaction between an electron beam generated by the device and an electromagnetic field excited and supported inside the waveguide to generate the electromagnetic radiation; the cylindrical structure is aligned coaxially with the electron beam in an interaction region of a magnetic field for conditioning and guiding the electron beam, in which the electromagnetic radiation is generated; A waveguide (110) wherein the diameter D of said cylindrical structure satisfies the condition D / λ>3, where λ is the wavelength associated with said frequency component.

15. 15. The waveguide of claim 14, wherein the inner surface comprises a two-dimensional periodic structure configured such that a radial distance between a longitudinal axis of the cylindrical structure and a position on the inner surface varies depending on both a longitudinal coordinate and an azimuthal coordinate of the position on the inner surface.

16. 16. A waveguide according to claim 14 or 15, wherein the inner surface has periodic variations in surface height that vary in two dimensions along the inner surface.

17. 17. The waveguide of claim 14, wherein the inner surface comprises a conductor, the inner surface being structured to increase the impedance of the waveguide in both longitudinal and azimuthal directions along the cylindrical structure.

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