This article conducts theoretical analysis and numerical calculation of the planar gyrotron, using a high-frequency interaction model with the double sheet electron beam and the transverse electromagnetic energy extraction. The model solves the electron momentum equation and the high-frequency field equation through numerical computation, which can roughly predict efficiency, output power, ohmic loss, and so on. On this basis, a 220-GHz double electron beam planar gyrotron is designed, with a transverse interaction efficiency of 43% and an output power of 700 kW. In order to verify the theoretical results, a 3-D interaction model is established in CST, and, by introducing the reflection protrusions close to the transverse open boundaries, the output power predicted using Particle-In-Cell (PIC) simulation is 640 kW, which distinctly overpasses the single electron beam scheme.

This paper designs a W-band planar structure double-beam magnetron injection gun based on the adiabatic compression theory and the momentum conservation law for a planar gyrotron. Using CST software for simulation and optimization, an obliquely placed cathode is introduced to correct the electron beam deflection when an axisymmetric magnetic field is used as usual. The design parameters of the electron gun are an anode voltage of 60 kV and a beam current of 5 A, with a transverse-to-axial velocity ratio of 1.15. The transverse velocity spread is 7.25%, and the longitudinal one is 10.12%. The electron gun was then fabricated and experimentally tested. The experimental trace spacing and deflection angle are consistent with the simulation. Furthermore, the electron data produced with the ParticleTracking module are used in the particle-in-cell (PIC) calculations. The PIC results exhibit the output power can achieve 62.5 kW, which is 85% of the theoretical prediction (73.8 kW).

To satisfy the space-borne tasks of meteorologic observation, planetary researches, and interferometric imaging, a new trial to develop a high efficiency Ka-band extended interaction klystron (EIK) is put on the agenda. In the high frequency circuit design, it is paid more attention to realizing high efficiency as far as possible; meanwhile, the circuit is kept stable using high lossy bunching cavities. The beam voltage and current are 17 kV and 0.72 A, respectively. The simulated output power is over 3 kW in the bandwidth of >100 MHz, and the maximum efficiency is above 30%. The preliminary test is finished with the beam transmission of 97% and the output power of 2.4 kW.

A new high-gain over-moded microwave pulse compression system has been found. The power gain of the system, in the optimal resonant state, has reached up to 280.04:1.00 for the rectangular TE1,0,20 resonant mode at 2.920GHz in S-band. Relative the traditional physical model before, the power gain of the new physical model increased by 51.86%; It has an important potential application to generate an ultra-high power microwave pulse of 28GW and 13ns in experiment rather than in theory. What the advanced technoloy and theory, see this letter to the international top SCI magzine of " IEEE Transactions on Microwave Theory and Techniques " .

Heat generated during lithium-ion batteries (LIBs) operation can lead to side reactions involving safety hazards, including fire and explosion, if not effectively dissipated. To address this challenge, the use of an efficient battery thermal management system (BTMS) is essential to regulate temperature within safe operating limits. Hence, this article provides a comprehensive review of lithium batteries and energy storage batteries, encompassing their classification, working principles, structural features, and heat generation mechanisms. A BTMS classification was proposed according to the most studied systems that were identified: Air-cooled, Liquid-cooled, Heat pipe-cooled, and phase change material (PCM)-cooled BTMS. Furthermore, a detailed analysis was conducted on PCM utilization in BTMS, according to its classification, selection criteria, properties enhancement methodologies, and applications. Notably, paraffins and inorganic compounds emerged as promising options for BTMS, with phase change temperatures ranging from 31.0 to 72.0 °C, latent heats from 35.0 to 210.0 J/g, and thermal conductivities of 0.5 to 9.3 Wm−1K−1. The integration of BTMS approaches, such as active and passive cooling, demonstrated potential in reducing power consumption and improving temperature uniformity within LIBs. Inorganic salt hydrates also showed promise in storing and managing heat during thermal runaway, suppressing its propagation, as supported by the ‘nail penetration test’. Additionally, the study highlights the growing utilization of industrial waste materials, such as bischofite, known for their cost-effectiveness. It also outlines future trends in BTMS, including active and passive cooling strategies, accurate heat generation modelling, and the potential of nano-enhanced PCM-cooled BTMSs, which could offer improved thermal conductivity. These findings offer a valuable resource for researchers, engineers, and industry professionals engaged in BTMS development and optimization, providing insights into the efficient management of heat for enhanced safety and performance.

A new ridge-loaded cavity structure with unequal-length slots is proposed to improve the bandwidth performance in extended interaction klystrons (EIKs). Based on the transverse-mode overlapping technology, such a structure is well suited to be driven by double sheet beams and exhibits a large efficiency bandwidth product. In contrast to the previously designed ridge-loaded structure, it operates in the longitudinal $\pi $ -mode instead of the longitudinal $2\pi $ -mode and has a larger characteristic impedance and smaller unloaded quality factor. It was designed as the idler cavity for a six-cavity circuit, and the simulation results predicted a maximum in-band output power of 275 W and a 3-dB bandwidth of 3.15 GHz, which expands the bandwidth by 750 MHz compared to the control circuit in the same operating conditions. The corresponding planar double sheet beams electron-optical system is also presented. The beam focusing electrode (BFE) is specifically designed with rod-shaped structure and outstretched structure to enable the two sheet beams to be compressed equally in the broadside direction, and the permanent magnet focusing structure is improved to avoid beam interception. Finally, the beams can pass through the 19-mm tunnel with 100% transmission efficiency, and the matching range of the magnet and electron gun is up to 1 mm.

It's presented here a general pattern for quantitative evaluation of impacts imposed by uncertainties brought directly from geometrical parameters on performance parameters for traveling-wave tube (TWT) design, in a holistic perspective in terms of distribution traits. For the sake of generality and built-up of pathways, artificial neural network (ANN), rather than closed-form solution, is employed for access to the mapping between geometrical parameters with interaction parameters, involving interaction impedance, detune parameter and attenuation constant. Furthermore, with the intermediate interaction parameters derived, the geometrical variations are eventually connected with TWT performance indexes like gain, bandwidth, insertion phase and even manufacturing yield. With such an ease on the association between the two somewhat distant analysis layers in general, a Monte-Carlo analysis is carried out to reveal the ramifications brought from multi-dimensional geometrical uncertainties on performance indexes. An embodiment of the analysis approach is made with double corrugated waveguide (DWC).

We have developed a compact 220-GHz extended interaction klystron (EIK) based on single-mode operation, which can generate 120W output power at around 220 GHz, the 1dB bandwidth is greater than 180MHz, the gain is greater than 30dB, and the duty cycle is 5%. The test results may be interesting. However, the bandwidth of EIK is insufficient, which affects its application fields. Therefore, we propose a G-band EIK based on multimode operation. PIC simulation shows that when the input power is 70mW, the EIK can provide 195W output power at around 220 GHz, and the 3dB bandwidth is greater than 4GHz.

An RF design of biperiodic multimode interaction circuit for ${G}$ -band extended interaction klystron (EIK) is presented to overcome the bandwidth limitation of conventional EIK operating in a single mode. The $\pi $ -mode and its adjacent ladder mode are chosen as the operating modes of the input and output cavities. The effect of beam loading and the presence of the waveguide port on the cavity characteristics of the output cavity operating in the multiple modes are investigated, including the coupling coefficients, the frequencies, and the hot quality factors. The bandwidth of the gain Section is broadened by the staggered tuning method. The 3-D particle-in-cell (PIC) simulation predicts a constant drive bandwidth of 4.5 GHz (exceeding 2% relative bandwidth) for the designed power amplifier around 220 GHz. Driven by a 21.4-kV, 0.25-A pencil electron beam, the amplifier can provide an output power of 195 W when the input power is 70 mW. The corresponding gain and electronic efficiency are 34.5 dB and 3.6%, respectively.

In order to meet the high-power source requirement of compact submillimeter-wave systems, a high-power G-band extended interaction klystron (EIK) has been developed at the Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS), and reported for the first time. The extended interaction circuit design based on over-synchronous voltage and high quality factor is proposed to enhance the output power and gain. In this manner, the designed EIK has achieved excellent test results compared with the same type of compact devices. Driven by a 20.3 kV, 198 mA pencil electron beam, the EIK can deliver a pulsed output power greater than 120 watts at around 0.22 THz, corresponding to a gain of 32 dB with a 5% duty cycle, and the average power and −1 dB bandwidth are 6 watts and 180 MHz respectively. Constrained by an axial magnetic field of about 1.03 T, the beam transmission is around 92% in RF operation.

In principle, if the beam is with initial transverse and axial velocity as well as propagating in period slow wave circuits, the combined Cherenkov and cyclotron resonances will exist, and the interaction will be enhanced. To illustrate and understand the influence of the combined resonance on the performance of devices intuitively, W-band sheet beam amplifiers with single-grating and staggered double-grating slow wave structures based on combined resonance and Cherenkov resonance are all designed and simulated, respectively. The results show that gain, bandwidth, and efficiency can be improved by utilizing multiresonances compared with Cherenkov resonance, which shows the attractive performance of the combined resonance. For the single-grating amplifier (SGA), the gain, bandwidth, and efficiency are improved by 1.68 dB, 2 GHz, and 0.45%, respectively. For the staggered double-grating amplifier (SDGA), the gain, bandwidth, and efficiency are improved by 0.85 dB, 5 GHz, and 0.42%, respectively. Besides, the comparisons of SGA and SDGA based on combined resonance are also presented and analyzed to provide a reference for the project implementation.

The design approaches of the overlapping-mode extended interaction klystrons (EIKs) are presented to satisfy the requirement for broadband terahertz power amplifiers. Since all the cavities are designed and tuned to operate in multiple-cavity modes, the overlapping-mode EIKs can provide high output power over a wider frequency band. The circuit characteristics of the overlapping-mode EIKs are studied, including the dispersion curve, the coupling coefficient, and the frequency interval between cavity modes. Moreover, a six-cavity EIK operating at 0.34 THz is designed to demonstrate the broadband output capability of the overlapping-mode EIKs. The $2\pi $ -mode and its adjacent axial mode, the $\pi $ /13-mode, are chosen as the operating modes of the designed EIK. The 3-D particle-in-cell (PIC) simulation predicts a 3-dB bandwidth of 2.9 GHz for the designed power amplifier at a small-signal level or in saturation. Driven by an input power of 10 mW, the amplifier can provide the output power of 3.9 W, and the corresponding gain is 25.9 dB. When the input power is 150 mW, the amplifier is partially saturated and can provide the output power of 33 W with a corresponding electronic efficiency of 1.23%.

Recent prominent analyses on impacts of fabrication errors tend to start from Pierce parameters by assuming a normal distribution on them. We manage to analyze the complicated effects of multi-dimensional uncertainties directly from geometrical tolerances and present a general pattern for multi-dimensional geometrical uncertainty analysis on field characteristics. Aided by artificial neural networks (ANNs) which would get hold of the cost surface quickly and serve as rapid interfaces with a calculation speed several orders faster than full-wave code, Monte Caro analysis is accessible and effective to simulate the actual probabilistic distributions through a large-volume sampling on neural networks. Under such data-driven perspective which circumvents sophisticated theoretical analysis, the variations of geometrical parameters are analyzed as an entirety from the viewpoint of distribution. The dynamics of features of distributions of three field characteristics as well as geometrical parameters are therefore possible to be delved and analyzed. Such an analysis pattern is general since none of the steps presented cannot be readily transplanted to other topologies.

For vacuum electronic devices (VEDs), the use of a hollow electron beam (HEB) increases the beam-wave interaction efficiency and permits a prominent decrease of the cutoff voltage in the focusing-electrode controlled electron gun. To obtain an HEB electron optics system (EOS) with stable propagation, lower ripple, high compression, and good laminarity, the issues related to the HEBs transmission characteristics in a uniform magnetic field are deeply investigated in this article. The studies on the Brillouin flow, which are different from the conclusion of the previous literature, are presented. Through combining the theoretical analysis and the simulation, the distinct motion ways of each layer in the HEB are clearly exhibited in both cases of the immersed flow and the partially shielding flow. This work can provide a meaningful reference for the design of a hollow beam EOS with high transmission and compression.

This article describes and evaluates the effect of random geometrical perturbations on resonance characteristics and output performance of extended interaction klystrons (EIKs). The perturbations, assuming a normal distribution, will result in random variation in resonance characteristics, including resonant frequency shift, quality factor shift, and field distortion. The results are demonstrated in a 220-GHz extended interaction cavity by combining theory, simulations, and experimental measurements. In addition, 3-D particle-in-cell (PIC) simulation and small-signal theory are employed to gain insights into the output performance instabilities caused by variation in the resonance characteristics. The comprehension of the factors that contribute to performance instability is fundamental to avoid excess costs in the fabrication process. Aided by the small-signal theory code with a calculation speed that is several orders faster than PIC simulation, we address the instability by applying cathode voltage adjustment technology, frequency tuning technology, and multiparameter optimization based on a genetic algorithm. Such analysis and improvement patterns are general for the EIKs operating in the terahertz regime.

Extended interaction klystrons (ElKs) have great potential to achieve high power and broad bandwidth. In order to further broaden the bandwidth of the output cavity, a barbell resonant cavity structure loaded by two ridges is proposed. This structure allows a uniform distribution of the electric field in two parallel rectangular tunnels. For the double sheet beam with a certain aspect ratio, it can be selected to operate either in the abnormal TM 11 mode or in the TM 21 mode. By adjusting the structural parameters, a novel transverse-mode overlapping scheme is presented, which allows the output cavity to provide considerable RF impedance over a frequency range.

This paper introduces the development progress of a compact 220-GHz Extended Interaction Klystron (EIK). And the EIK can produce more than 100-W output power near the 220-GHz operating frequency, while the operating voltage is less than 20kV, the power bandwidth is more than 150MHz, the gain is more than 30dB, and the duty cycle is 5%. The subsequent optimization of EIK is in progress.

In this article, the design and experiment of a hollow electron beam (HEB) electron optics system (EOS) for Ka-band extended interaction klystrons (EIKs) are presented. To realize the fast switch of the current emission at a low cutoff voltage, an electron gun with two focus electrodes (FEs) is chosen. The emitting surface of cathode is a ringed spherical surface. The first focus electrode (FE1) is around the cathode, and the second focus electrode (FE2) is set in the central hole of the cathode. The current emitted from the cathode surface is about 2A, when the operating voltage is 25 kV. Three simulation codes, Egun, Superfish, and CST, are used for designing the electron gun and the permanent magnet focusing system (PMFS). Some sensitivity analyses with respect to the PMFS’s critical parameters are presented. The simulation shows the dc beam transmission is 100%. The electron beam, confined by 6000 Gauss uniform field, propagates through the drift tube of 37 mm with good laminarity and small ripple. The emission current can be suppressed when the voltage of the FEs is −3.4 kV. According to the results of simulation, the Ka-band EIK had been constructed and the hot-test experiments had been fulfilled in succession. The experimental results exhibit that the dc beam transmission is about 99% and the beam can sustain 98% transmission at high frequency (HF) operation. In addition, the output power is higher than 8 kW in the bandwidth of over 100 MHz.

The mode overlapping technology is employed in extended interaction klystron (EIK) to broaden the bandwidth. For a compact resonant cavity with small number of gaps, the weak-coupling structure enables the superposition of $2\pi$ mode and the adjacent longitudinal mode. The two operating modes are carefully optimized to have similar high-frequency characteristics and power extractions. Finally, a simple two-cavity circuit verifies the feasibility of the scheme.