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In this paper, multiphysics field simulation is applied to analyze the temperature distribution of Ka-band U-shaped microstrip line planar TWT considering the thermal losses induced by ohmic loss and electron collision losses. The beam-wave interaction of the planar TWT is analyzed by using CST particle-in-cell (PIC) solver, at the same time the thermal losses distribution is recorded, which will be the heat source. The simulation results show that the high temperature with a peak value of 263 °C.

The four-way quasi-optical power combiner consists of a pair of phase-correcting mirrors with Gaussian beam output is proposed in this paper. Applying the geometric optics approximation and the scalar diffraction theory, a numerical simulation code of the quasi-optical power combiner is developed. The proposed power combiner is validated by a commercial simulation software, and the results show that the combination efficiency of 94% at 30 GHz is obtained. The proposed quasi-optical power combiner features high power, high efficiency, high purity, and simple structure.

In this paper, a novel slow-wave structure (SWS) called folded V-shape groove waveguide SWS is proposed. The high frequency characteristics of this SWS is studied. An input and output waveguide transition structure, which is appropriate for this new kind of SWS is put forward. The transmission loss of the folded V-shape groove waveguide is lower than that of folded rectangular groove waveguide. The dimension of the folded V-shape groove waveguide is larger than that of the folded rectangular groove waveguide at the millimeter waveband, even at terahertz waveband. Based on this kind of SWS, a W-band sheet beam traveling-wave tube is studied, whose beam-wave interaction is calculated by means of the simulation software. The calculation results show that the output power can be over 260 W within 3-dB bandwidth from 84 to 98 GHz, the gain can reach up to 36 dB, and the electron efficiency is 12.33% at the center frequency.

A novel ridge-loaded staggered single-slot rectangular coupled-cavity traveling-wave tube (CC-TWT) operating at $X$ -band is presented. It features large interaction impedance and good thermal dissipation with a moderate bandwidth. Compared with the existing staggered single-slot rectangular CC-TWT and Hughes-type TWT, this structure has the advantage of large coupled impedance and high electron efficiency, which makes it potentially useful for miniaturization in CC-TWT. The electromagnetic characteristics and the beam–wave interaction based on this slow-wave structure are investigated. The calculation results predict that it potentially could provide saturated output power over 20 kW from 8.5 to 9.8 GHz when the cathode voltage is set from 25.4 to 26.4 kV and the beam current is 5 A, respectively. The corresponding saturated gain and the electron efficiency can reach over 34.4 dB and 15.2%. From 8.6 to 9.5 GHz, the gain is even over 38.6 dB, and the electron efficiency is more than 16.9%. The cold test results show that the voltage standing wave ratio of the high-frequency structure is below 2 at the range of 8.5–10 GHz.

Understanding of the anomalous transport attributed to short-scale length microturbulence through collective scattering diagnostics is key to the development of nuclear fusion energy. Signals in the subterahertz (THz) range (0.1–0.8 THz) with adequate power are required to map wider wavenumber regions. The progress of a joint international effort devoted to the design and realization of novel backward-wave oscillators at 0.346 THz and above with output power in the 1 W range is reported herein. The novel sources possess desirable characteristics to replace the bulky, high maintenance, optically pumped far-infrared lasers so far utilized in this plasma collective scattering diagnostic. The formidable fabrication challenges are described. The future availability of the THz source here reported will have a significant impact in the field of THz applications both for scientific and industrial applications, to provide the output power at THz so far not available.

A two-section Folded rectangular groove waveguide (FRGWG) Slow wave structure (SWS) Traveling wave tube (TWT) with large dimension of beam tunnel is studied. Compared with the Folded waveguide (FWG) under the same size parameters conditions, the interaction impedance and center frequency of the FRGWG are higher. The advantage is that a beam tunnel with large dimension can be applied to the FRGWG without the influence caused by signal decrease, reflection and oscillation. The microwave amplification capability based on beam-wave interaction is obtained through the particle-in-cell method. This circuit structure can produce an output power of over 100W ranging from 136 to 142GHz when the operation voltage and beam current are set as 18.4kV and 150mA, respectively, for a 95mm long circuit.

A wideband coaxial line to double-ridge waveguide window for broadband high power THz TWT has been studied in this paper, which can cover the 270–370 GHz with a ultra-bandwidth over 0.1 THz. Based on the mode conversion theories and impedance matching techniques, the broadband transition of coaxial line to double ridge waveguide is designed. In addition, the diamond is adopted to design the broadband double ridged waveguide window. The characteristics of the transition are analyzed by using the full-wave analysis software. According to the simulated results, the reflection coefficient is less than −20 dB and the VSWR is less than 1.2 in the 270–370 GHz.

A 0.65 THz traveling-wave tube was designed based upon truncated sine waveguide slow-wave structure. The high frequency characteristics and transmission characteristics are analyzed and calculated by Ansoft High frequency simulation software. We have also studied and simulated the beam-wave interaction of this truncated sine waveguide traveling-wave tube. The results show that the peak output power is 270 mW from 640 GHz to 660 GHz with synchronous voltage of 18.9 kV, operation current of 11 mA and input power of 1.25 mW.

A new high-power microwave-generator based on metamaterial (MTM) slow wave structure is studied. The microwave structure is formed by inserting a MTM plates loaded with 2D split ring resonators (SRRs) into a rectangular waveguide. The dispersion characteristics of the unit cell are obtained by using eigenmode simulations in the High Frequency Structure Simulator (HFSS). In addition, the transmission properties and the beam-wave interaction characteristics are simulated in the Computer Simulation Technology (CST). The simulation results indicate that the novel metallic MTM backward wave oscillator (BWO) can produce 20.05 MW output peak power and an interaction efficiency of 45.56% at the frequency of 33.157 GHz.

The ridge loaded azimuthal supported angular log-periodic strip meander line slow wave structure (SWS) is presented in this paper. The dispersion characteristics and coupling impedance of the SWS are calculated. According to the simulation results of beam wave interaction, the planar travelling wave tube(TWT) with SWS can give the output power of 136.3W, the electron efficiency and gain approach 5.6% and 9.6dB, respectively, at 39GHz under a single fan-shaped radial sheet beam voltage of5250Vand current of 0.46A.

A new slow wave structure (SWS) of azimuthal support angular log-periodic strip line SWS is presented in this paper. An attractive property of the new structure is that the ability of resistance to electron bombardment is better than microstrip SWS. Applied a single radial sheet beam with the work voltage of 5920V and the current of 0.6A, the beam-wave interaction results show that the maximum output power, gain and electron efficiency are 300.3W, 14.8dB and 8.46%, respectively, in Ka band.

A conformai microstrip angular log-periodic meander line(ALPML) traveling wave tube(TWT) based on quartz substrate is studied in this paper. In order to decrease the attenuation of dielectric substrate and eliminate the charge accumulation, a conformal microstrip is adopted. Conformal microstrip remove the unnecessary dielectric substrate and remain the dielectric substrate in the microstrip metal layer below. The remained dielectric substrate is as same shaped as the metal layer. By simulation, this traveling wave tube can reach 25W power output in 32GHz, which in condition of voltage 2300V and current 0.2A. The gain and efficiency is 14dB and 5.6%, respectively. The 3dB bandwidth is 10GHz from 27.5GHz to 37.5 GHz.

A novel slow-wave structure (SWS) named angular log-periodic folded groove waveguide was proposed in this paper, which mainly used in traveling wave tube (TWT) for G-band. Due to the design idea owing the combination of folded groove waveguide and log-periodic form, this new SWS possess several advantages from them. Low operation voltage and weak dispersion of electromagnetic wave are merits of them. In addition, a modified equation to calculate the phase velocity in radial direction was proposed. In the end, one angular log-periodic folded groove waveguide was designed which owing 38.8W output power at 198GHz, the gain is 18.8dB when operation voltage is set to 8080V.

Terahertz (THz) electromagnetic (EM) radiation in beam-plasma system under different plasma distribution has been simulated using particle-in-cell (PIC) method in this paper. The calculation results show that the electromagnetic radiation frequency under radially non-uniform plasma distribution is lower than that under uniform plasma distribution, which is good agreement with the theoretical analysis. The related physical analysis about the simulation results is given out. This work will give a better physical understanding of beam-plasma system and provide guidance to the project practice

Cascade high-power microwave generator is an effective solution to provide a high level of miniaturization device. In this paper, we present a kind of novel cascade backward wave oscillator operating in the C band. The drift tube is employed to design a novel cascade backward wave oscillator. The phase synchronization of two output ports are analyzed by using Computer Simulation Technology (CST). Meanwhile, the CST Particle Studio (PS) is adopted to investigate the performance of the cascade backward oscillator. The Particle-in-cell (PIC) simulation results show that the novel cascade backward oscillator is capable of achieving over 51.77% electronic efficiency from 4.8344 GHz to 4.8687GHz. Meanwhile, the maximum electronic efficiency can reach 82.44%% corresponding to a peak output power of 14 MW at 4.8466GHz.

In this paper, a novel slow-wave structure (SWS), called quasi-parallel-plate (QPP), is proposed for terahertz (THz) backward-wave oscillator BWO design. Compared with the conventional SWSs, the novel SWS has a wider “cold” bandwidth and higher interaction impedance. The Particle-in-cell (PIC) results show that the BWO can produce over 0.82 W output power in the operating frequency range from 0.82 to 1 THz by utilizing an operating voltage range from 5 to 10 kV. The interaction efficiency over the entire operating frequency band is above 2.8%. This SWS, which employing a circular electron beam of 3 mA, can be considered as a promising THz SWS for BWO design with characteristics of moderate operating voltage, wide tunable bandwidth, high efficiency, and compact structure.

A W-band backward wave oscillator (BWO) based on metamaterial (MTM) slow wave structure (SWS) is presented as a novel high power microwave generator. Particle-in-cell (PIC) simulation is performed to evaluate the efficiency of the W-band MTM-based BWO (MTMBWO), and the MTMBWO can reach saturated output power of 2.78MW with an electronic efficiency of 31.68% at frequency of 84.87GHz.

The paper describes the design of an X-band coupled-cavity traveling-wave tube (CC-TWT) based on the reentrant double-staggered ladder coupled-cavity slow wave structure (SWS) using High Frequency Structure Simulator (HFSS) and particle-in-cell (PIC) code in Computer Simulation Technology (CST) Particle Studio. When the cathode voltage and cathode current are 25.9 kV and 5 A, respectively, the PIC simulation results show that the corresponding saturated output power is over 20kW from 8.6 to 9.7 GHz, the maximum output power can reach 28.8 kW at 9.2 GHz, and the electronic efficiency and the gain can reach over 15.6% and 40 dB.

The design of fan-shaped metal loaded helix slow wave structure for a dual-band (Ka/Q) traveling wave tube is presented in this paper. The beam-wave interaction simulation predicts a minimum output power of 199/191 W, minimum electronic efficiency 15.1%/12.5%, and maximum gain of 50.1/49.9 dB, respectively, for Ka-band(29-31GHz) and Q-band(43.5-45.5GHz).

In this paper, we proposed a novel metamaterial slow wave structure (SWS) for backward wave oscillator (BWO) to develop the high power microwave source. The high frequency characteristics of the SWS are analyzed by the HFSS, the transmission properties and the beam-wave interaction process are simulated in the CST Studio Suit. The simulation results reveal that the BWO based on the novel metamaterial SWS can produce 0.552MW output power and an interaction efficiency of 9.84% at the typical frequency of 31.6GHz.

A 1D frequency-domain nonlinear model for illustrating the beam-wave interactions of sine waveguide (SWG) traveling-wave tubes (TWTs) was studied. Our model considered space-charge fields and Ohmic losses to make the model closer to practical situations. The sheet beam was split into a series of rectangular electron plates in the axial direction, and the space-charge field was calculated by solving Green's function. The dynamic equations and relativistic equations of motion were solved self-consistently to obtain the nonlinear characteristics of the power saturation, as well as the electron velocity, phase space distributions, etc. A 0.22 THz SWG TWT was used to illustrate and verify the validity of the theoretical model. The output power and gain results were in good agreement with those from the Computer Simulation Technology (CST) 3D particle-in-cell simulation. In addition, the code developed based upon the theoretical model produced faster results than the CST simulation.

A new type of folded frame slow-wave structure (SWS) is introduced and used in the design of a low-voltage, high-efficiency, and widebandwidth millimeter-wave traveling-wave tube (TWT). The high-frequency characteristics of the folded frame structure, including dispersion properties, coupling impedances, and reflection characteristics are investigated. The beam-wave interaction of the TWT with the folded frame SWS working at the millimeter-wave frequency range is also calculated using 3-D particle-in-cell algorithms. The simulation results reveal that with sheet electron beam parameters of 6000 V and 0.2 A, the average output power and electron efficiency can reach 196 W and 16.3%, respectively. Compared with the symmetric double V-shaped microstrip meander-line SWS, the folded frame SWS has larger coupling impedances and can generate higher output power.

A novel ridge-loaded folded waveguide slow-wave structure has been firstly employed to manufacture a W-band continuous wave traveling wave tube (TWT). This letter reports the processes of the design and experimental test for this TWT. From the experimental results, over 25-W output power are produced within the operation bandwidth from 93.1 to 94.8 GHz, which is in accordance with the simulation results.

A novel slow-wave structure called ridge-vane-loaded folded waveguide combined with pencil electron beam has been proposed for millimeter-wave traveling-wave tubes. The high-frequency characteristics including the dispersion properties and the interaction impedance of this kind of structure have been analyzed by means of an equivalent circuit based on the transmission-line cascading network. The theoretical results agree well with those obtained by the 3-D electromagnetic high-frequency simulation software. The nonlinear interaction between the electron beam and the electromagnetic field is investigated with the help of the Computer Simulation Technology Particle Studio 3-D particle-in-cell (PIC) code. The PIC simulation results revealed that this kind of structure could produce about 56 W of peak output power at 0.22-THz when the cathode voltage and current of the pencil electron beam are set to 14.65 kV and 50 mA, respectively. Moreover, the maximum gain and interaction efficiency can reach 37.5 dB and 7.7% at 0.22 THz, respectively. A simulated 3-dB bandwidth of ~ 30 GHz is demonstrated.

A novel slotted helix slow-wave structure (SWS) is proposed to develop high power, wide-bandwidth, high reliability millimeter-wave traveling-wave tube (TWT). This structure, which can improve the heat dissipation capability of the helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix. In this paper, thermal stress analysis, the electromagnetic characteristics and the beam-wave interaction of this structure are investigated. The conclusions of this paper will be a great help for the design of millimeter-wave traveling-wave tube.

A method to estimate output power for sheet-beam traveling-wave amplifiers is presented. Two traveling-wave tubes are calculated by this method, and the results are compared with those of particle-in-cell simulation.

A 340GHz backward wave oscillator (BWO) based on the sine waveguide and pencil electron beam is presented as a novel terahertz radiation source. The particle-in-cell (PIC) simulation results predicts that this device can produce the output power of over 2.7W in the frequency range of 335.8–348.5GHz by utilizing a 20mA pencil beam and adjusting the voltage from 12kV to 14 kV.

This paper describes a fan-shaped metal-loaded helix slow-wave structure (SWS) to develop ultra-wideband traveling-wave tube with low gain fluctuation. The electromagnetic characteristics and beam-wave interaction of this structure are calculated. The simulation results show that the helix TWT gain is more than 42dB and the signal gain fluctuation of the TWT is less than 2.5dB in a frequency range from 15 to 35 GHz. In addition, the maximum output power can reach 199 W at 21 GHz, corresponding to the maximum electronic efficiency is 16.6%.

A collaboration between UC Davis, Lancaster University, Beijing Vacuum Electronics Research Institute (BVERI), and the University of Electronic Science and Technology of China (UESTC) is developing a 346 GHz backward wave oscillator (BWO) for use as a source in plasma fusion diagnostics, medical, biological, and security imaging systems. Development of new electron gun optics that achieve almost 100% beam transmission based on particle-in-cell simulations is presented along with comparisons of the cold and hot beam performance. Also, a CVD diamond pillbox window design is presented. Additionally, the mechanical layout of the devices is being completed and prepared for fabrication.

The small signal gain of the square helix TWT has been calculated based on the improved tape model. It is clearly shown that the square helix TWT possesses higher peak gain than that of the equivalent round helix TWT, which indicates higher output power under the identical device length.

The propagation characteristics were investigated of an open elliptical cylinder comprising a uniaxial anisotropic metamaterial. The dispersion relation for hybrid modes in this cylinder was examined theoretically. It is shown that forward and backward waves can be supported by such a metamaterial cylinder. Even and odd modes have different losses in a realistic anisotropic elliptical cylinder. The forward wave can propagate longer distances than the backward wave because of its lower loss. The light can propagate backward on the cylinder without the limit of structure size. The odd modes have higher operating wavelengths than the even modes. The extraordinary properties in this structure are identified as multilayer plasmons. The validity of the effective medium approximation of this structure is examined.

A novel slow-wave structure called V-shape folded rectangular groove waveguide is proposed to develop high-power, wide-bandwidth, and high-efficiency millimeter-wave traveling-wave tube. This structure evolves from a conventional rectangular groove waveguide bending the groove with V-shape along its longitudinal direction, which can operate with the sheet electron beam. In this paper, the electromagnetic characteristics and the beam-wave interaction of this structure operating in the V-band are obtained. From our calculations, this circuit structure possesses low transmission loss and can produce an output power of over 900 W ranging from 56 to 65 GHz when the cathode voltage and beam current are set to 12.8 kV and 500 mA, respectively. The corresponding gain and electron efficiency can reach over 36.5 dB and 14%, respectively.

A novel slow-wave structure (SWS) called the folded rectangular groove guide, its electromagnetic characteristics, and the beam-wave interaction are presented. This structure, evolved from a conventional rectangular groove guide by bending the groove along its longitudinal direction, can operate with the sheet electron beam or the circular electron beam. From our calculations, this SWS possesses larger interaction impedance and lower ohmic loss than those of a folded rectangular waveguide with the same size. This circuit can produce output power of over 260 W with a sheet electron beam in the 3-dB bandwidth range of 88.5.5-98.5 GHz when the cathode voltage and beam current are set to 19.45 kV and 150 mA, respectively, whereas the folded rectangular waveguide can produce output power over 245 W in the 3-dB bandwidth range of 84-89 GHz.

In this paper, a new simple equivalent circuit model for analysis of dispersion and interaction impedance characteristics of ridge-loaded folded-waveguide slow-wave structure is presented. In order to make the computational results more accurately, the efiects of the presence of the beam-hole and discontinuity due to the waveguide bend and the narrow side dimension change of this kind of structure were considered. The dispersion characteristics and the interaction impedance are numerical calculated and discussed. The analytical results agree very well with those obtained by the 3-D electromagnetic high-frequency simulation software. It is indicated that the equivalent circuit methods are reliable and high e-ciency.

In this paper, we present a simple dual-band patch antenna that radiates at 920MHz and 2.4GHz effectively. The patch antenna is designed with meander slot and shorting probe to increase the current path and reduce the resonant frequency. In addition, a high efficiency, dual-band rectifier is also proposed here. The rectifier is designed by a four-stage voltage doubler topology with lump inductors added, and the resonant frequency can be tuned independently. At an input power level of 15dBm, the experimental result shows a RF-to-DC conversion efficiency up to 78% at dual-band can be achieved. The corresponding DC output voltage is 7.26V and 6.82V respectively with a 9.1kOhm load.

This paper presents a tapered ridge-loaded folded waveguide (FWG) slow-wave structure (SWS) for broadband and high power millimeter wave traveling wave tube (TWT). The radio-frequency characteristics including dispersion properties, interaction impedance, S-parameters are analyzed. And based upon these results, the nonlinear large signal performance of the tapered ridge-loaded folded waveguide TWT working in W-band is simulated by 3-D particle-in-cell code. In the same ridge length, the tapered FWG has lower reflection and radio-frequency loss than the normal ridge-loaded FWG. Besides, the tapered ridge-loaded FWG TWT also has higher electron efficiency and larger bandwidth, which is more suitable for millimeter-wave TWT.

The electron beam interaction in a novel slow-wave structure (SWS) called dielectric-lined azimuthally periodic circular waveguide (DLAP-CW) is analyzed in a linear frame. Moreover, the linear gain characteristics of the DLAP-CW are obtained by the self-consistent relativistic field theory. Analytical solutions for the hot dispersion characteristics are derived, and the complicated dispersion equations have been numerically solved with MATLAB. The small-signal growth rate is calculated for dimensions of the improved SWS and the parameters of the electron beam. It is shown that selecting the appropriate thickness and location of the metal rods increases the small-signal gain (dielectric constant held fixed). In addition, the gain of the DLAP-CW increases as the beam current increases, and the beam voltage not obviously influences the small-signal gain. Furthermore, a comparison of the small-signal gain of this structure with a conventional dielectric-lined circular waveguide (DL-CW) is made, and the results validate that the novel SWS has an advantage over the DL-CW on the electron efficiency, potentially resulting in a higher gain traveling-wave-tube circuit.

A folded-waveguide (FW) traveling-wave tube (TWT) with two electron beams, which operates at the higher order mode, is simulated. Operating with two electron beams means that a larger beam current can be used for a higher output power. Meanwhile, the electric field density of the fundamental mode is not the strongest at the center of the beam channel, so the competition of the fundamental mode is significantly suppressed. A four-section two-beam FWTWT at 140 GHz is designed to get 100 W of average power. From the simulation results, we can see that this kind of tube is unstable if the gain per section is over 11 dB, because both fundamental and band-edge modes are strongly excited. Then, another way for a stable FWTWT operation with two electron beams by loading with dielectric is also presented in this paper. The results presented here can provide a new way to obtain high power radiation at the terahertz frequency.

The design and simulated performance of a traveling-wave tube (TWT) constructed by combining a folded-waveguide (FW) slow-wave circuit with arrays of 2-D photonic crystals (PhC) are presented. Numerical results reveal that the Pierce interaction impedance of the FW circuit with PhCs is similar to the circuit without PhC arrays. The gain, output power, and efficiency of TWTs with and without PhCs are also similar when the circuit dimensions are identical; however, the TWT with PhCs can filter out nonoperating modes, which may improve the stability of the circuit shielded with PhCs when compared to the same circuit shielded by metal walls.

Stable sheet electron-beam transport is critical for sheet-beam microwave device which is attractive for high-power millimeter wave to terahertz-regime radiation. This paper studies the stable sheet-beam transport in periodic nonsymmetric quadrupole field. First, the conditions for stable round- and sheet-beam transport in periodic magnetic quadrupole field are deduced. In the deduction, we find that the symmetric quadrupole field and the space-charge field of sheet beam are not well matched. In order to settle this problem, we use periodic nonsymmetric quadrupole field instead of periodic symmetric quadrupole field to transport sheet beam. Finally, 3-D PIC simulations verify the conditions for stable sheet-beam transport and show that periodic nonsymmetric quadrupole field is intrinsically well suited for sheet-beam transport.

A novel winding microstrip meander-line slow-wave structure (SWS) has been proposed to develop low-voltage and high-power millimeter-wave traveling-wave tube. This structure, which interacts with a round electron beam, evolves from a V-shaped microstrip meander-line SWS. The electromagnetic characteristics and beam-wave interaction of this novel structure are calculated in this letter. As is seen from the results, traveling-wave tubes with this novel circuit can provide over 130-W output power ranging from 58 to 63 GHz. In addition, the maximum electronic efficiency may reach 10% at 61 GHz.

With instantaneous and in situ characteristics, mode discriminators based on mode-selective coupling principles attract much attention, but their working bandwidth is restricted by the distribution of the equal distance between adjacent holes and the equal radius of all holes. Meanwhile, the equal-interval and unequal-radius distribution of holes can increase the bandwidth of the mode discriminators remarkably. Therefore, the basic theory, designing method and example of the mode discriminators based on the equal-interval and unequal-intensity (i.e. various radii of holes) coupling are brought forward in this paper. The formulas of coupling intensity in terms of binomial distribution and Chebyshev distribution are also presented. The calculation shows that the working bandwidth of the mode discriminators based upon mode-selective coupling according to binomial distribution or Chebyshev distribution can reach 15% to 19%, which is twice over that of equal-interval and equal-intensity coupling mode discrimin...

Properties of traveling wave-beam interaction in a centered dielectric-rod loaded, arbitrarily-shaped helical groove slow-wave structure (SWS) are investigated for a thin annular electron beam. The “hot” dispersion equation is obtained by means of the self-consistent field theory, and the small signal analysis is carried out including the effects of the dielectric-rod parameters and the groove shapes. The numerical results show that the bandwidth of the helical groove TWT is expanded by loading dielectric-rod, however, the small-signal gain is reduced; and when the groove shape changes from the swallow-tail shape to the triangle shape, the working frequency increases , while the peak gain decreases.

Elliptical waveguides and ridged waveguides have found broad applications in many microwave structures. The elliptical waveguide with double infinite thin ridges has been formulated using the mode-matching method. Exact closed-form expressions for eigenvalue problem of all TE and TM modes are presented. Numerical results suggest that the elliptical ridged waveguides have larger bandwidth than that of circular ones.

A simple but reasonable approach to the cold dispersion analysis of a coaxial arbitrary-shaped groove cylindrical waveguide is presented in the fast-wave regime for potential application in wideband gyro-traveling-wave tubes (gyro-TWTs). The unified dispersion equation of this structure is obtained by using an approximate field-theory analysis, in which the profile of the groove is approximately replaced by a series of rectangular steps, and the continued relation of the fields between two adjacent steps and the matching conditions at the interface between the groove region and central region are investigated. The dispersion characteristics of the disk-loaded structure obtained by modifying above results have been validated against those reported by Kesari et al. Meanwhile, the dispersion characteristics of arbitrary-shaped groove, such as the triangle-groove-loaded one are proved to agree well with computer simulation technology (CST) microwave studio simulation. The results of numerical calculations of the dispersion relation shows that the adjustment of structure parameters led to the possibility of widening the straight-line portion of omega-beta dispersion characteristics, which is required for wideband TWT performance in view of widening the bandwidth of resonance between the beam-mode and the waveguide-mode. Comparison of several different shape groove-loaded structures shows that the coaxial inverted trapezoid groove one shows the most potential application in wideband gyro-TWT because its transverse electric field is the greatest so that can interact effectively with the electron beam.

The slow-wave characteristics taking account of space harmonics for confocal corrugated elliptical waveguides are presented. By using the field-matching method, the dispersion equation, and the mean interaction impedance for odd hybrid modes of this structure are derived. Based on our results, changing the waveguide eccentricity can improve the dispersion characteristics and the interaction impedance for oEH01 mode

The understanding of plasma turbulence in nuclear fusion is related to the availability of powerful THz sources and the possibility to map wider plasma regions. A novel approach to realize compact THz sources to be implemented in the plasma diagnostic at NSTX experiment (Princeton Plasma Physics Laboratory, USA) is reported.

A sine waveguide traveling-wave tube with cylindrical electron beam tunnel is proposed to amplify the terahertz wave. In this paper, the high frequency characteristics of sine waveguide with cylindrical electron beam tunnel are calculated by 3-D high frequency simulation software. From the particle-in-cell simulation results, this beam-wave interaction circuit can produce several watts ranging from 0.325THz to 0.347THz.The maximum output power is 27.6W at 0.34THz, and the corresponding gain reaches 31.4dB.

The development of collective scattering diagnostics is essential for understanding of the anomalous transport attributed to short scale length microturbulence which poses a threat to the development of nuclear fusion reactors. Signals in the sub-THz range (0.1 – 0.8 THz) with adequate power are required to probe the plasma. A joint international effort is therefore devoted to the design and realization of novel backward wave oscillators at 0.346 THz and above with output power in the 1 Watt range to replace the bulky, high maintenance optically pumped FIR lasers so far utilized for this plasma diagnostic.