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Generation of rogue waves in gyrotrons with high excess over the threshold
摘要： Many physical systems exhibit behavior associated with the emergence of the so-called rogue waves which represent dramatically high-amplitude events that occur with low probability but much more frequently than expected in ordinary wave statistics [1]. For example, in laser physics and optics rogue waves arise in the process of supercontinuum generation and represent pulses of ultra broadband light with extremely high peak power [2]. In this paper within the framework of the average approach and in direct 3D PIC (particle-in-cell) simulations we demonstrate that rogue waves can also appear in gyrotrons operating with high excess over the threshold. The mechanism of extreme spikes formation is related to simultaneous cyclotron interaction of a gyrating electron beam with forward and backward waves near the waveguide cutoff frequency as well as with the longitudinal deceleration of electrons. From the practical point of view, experimental observation of the rogue waves generation in gyrotrons can be interesting as a method for production of high-power millimeter-wave radiation with an ultra broadband spectrum. The required exceeding over the threshold can be achieved for routine parameters of the driving electron beams formed by the magnetron-injection guns due to operation at the lowest modes of microwave cavities.
关键词： high-power millimeter-wave radiation,rogue waves,gyrotrons,ultra broadband spectrum
更新于2025-09-10 09:29:36
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NEW STABILIZATION TECHNIQUE TO PREVENT PARAMETRIC OSCILLATIONS IN A 35 W C-BAND ALGAN/GAN MMIC HIGH POWER AMPLIFIER
摘要： In this paper, a novel stabilization scheme to prevent parametric oscillations in power amplifiers is presented. Based on a new oscillation detection approach, the inductive degeneration technique was used, for the first time, to successfully stabilize a high-power amplifier and prevent parametric oscillations. A 0.15 μm AlGaN/GaN Microwave Monolithic Integrated Circuit high power amplifier operating at 5.8 GHz with 10% fractional bandwidth was designed and successfully stabilized using this approach. The proposed (4.7 × 3.7) mm2 three-stage amplifier achieves a saturated output power of 35 W with 29% power added efficiency and a large-signal gain of 26 dB.
关键词： AlGaN/GaN,MMIC,high power amplifier,stabilization technique,parametric oscillations
更新于2025-09-10 09:29:36
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Photo-electrochemical stability of copper oxide photocathodes deposited by reactive high power impulse magnetron sputtering
摘要： Copper oxide thin films were deposited by a reactive high power impulse magnetron sputtering (r-HIPIMS) on glass substrates with a SnO2:F (FTO) layer. The pulse magnetron discharge was analyzed via the radio frequency (RF) Sobolewski probe, used for the time-resolved measurement of ion flux density on the substrate. Pulsed discharge current and voltage waveforms were analyzed. It was found that the pulse magnetron discharge worked in a self-sputtering mode with a stable or slightly growing discharge current after pulse discharge stabilization. As-deposited copper oxide films exhibited a certain degree of crystallinity, as identified by XRD, which was further improved after postdeposition annealing at 550 oC in the air. After annealing, the mixture of CuO and Cu2O crystallites was usually found in the films and in a few cases CuO0.96 phase was detected. Deposited films exhibited a p-type conductivity and relatively high photocurrents in the cathodic region after the postdeposition annealing. The highest photocurrent density of ip ≈ 1.1 mA cm-2 at potential -500 mV vs. Ag/AgCl was detected for films with a thickness of 1200 nm.
关键词： magnetron discharge,photocurrent,high power impulse magnetron sputtering,reactive sputtering,copper oxide,photocathode
更新于2025-09-10 09:29:36
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Investigation of an $X$-Band Long Pulse High-Power High-Gain Coaxial Multibeam Relativistic Klystron Amplifier
摘要： Increasing the output power of the microwave is one of the most important development directions for high-power microwave (HPM) technology. However, when the output power is increased, the radio frequency breakdown would occur owing to superhigh electric field strength. This problem limits the power handling capability of a single-HPM generator, and this problem becomes more serious for high-frequency bands and long pulse. One solution to overcome this problem is coherent power combining, and coherent power combining can achieve an equivalent power of the order of TW. The relativistic klystron amplifier (RKA) is a promising candidate for coherent power combing owing to its character of controllable frequency and steady phase. However, the radiation power of RKA quickly decreases when the source is scaled up to higher frequencies such as X-band, and moreover, the multigigawatts long pulse radiation from RKA at the X-band has not yet been obtained experimentally. In this paper, we present investigations into an X-band coaxial multibeam RKA, The power handling capability was increased by introducing 20 electron drift tubes and a four gaps extended interaction output cavity. The amplitude uniformity of the multiple electron beams was improved by optimized the anode and cathode configuration. Then, a radiation power of 2.2 GW with pulsewidth of 120 ns is generated experimentally; the working frequency and amplifier gain are 9.4 GHz and 50 dB, respectively.
关键词： Coaxial multibeam relativistic klystron amplifier (CMB-RKA),X-band,long pulse,high-power microwave (HPM)
更新于2025-09-10 09:29:36
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High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally induced mode instability suppression
摘要： An all-?berized and narrow-bandwidth master oscillator power ampli?cation (MOPA) system with record output power of 4 kW level and slope ef?ciency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability (TMI) suppression. The stimulated Brillouin scattering (SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of ～0.025, 0.17 and ～0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be >5 times in which tandem pumping increases the TMI threshold of >3 times. The beam quality (M 2 factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the in?uence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth ?ber ampli?ers.
关键词： optimization,design,laser ampli?ers,narrow linewidth,high power laser,laser systems,modeling,advanced laser technology and applications,?ber laser and applications
更新于2025-09-10 09:29:36
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A Ku-band coaxial transit-time oscillator with Pierce-like cathode under permanent magnet packaging
摘要： A novel Ku-band coaxial transit-time oscillator (TTO) with Pierce-like cathode is proposed in this paper. TTO has the characteristics of low space-charge effect and short interaction distance. Combining with these features, we design a novel Pierce-like cathode to lower the demand for the guiding magnetic field. The guiding magnetic field intensity is reduced to about 0.32T by loading the Pierce-like cathode, but the magnetic field intensity is not a stable value, it fluctuates at 0.32T because of the properties of permanent magnet. To achieve the light and small goals of TTO, we design a novel permanent magnet structure with NdFeB. Based on the research, the typical simulation result is that when the diode voltage is 440kV, the beam current is 11kA, the guiding magnetic field is about 0.32T, the device can output 1.46GW microwave pulse at 14.2GHz. The power conversion efficiency is about 30%.
关键词： coaxial transit-time oscillator,Pierce-like cathode,permanent magnet packaging,Ku-band,high power microwave
更新于2025-09-10 09:29:36
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A Novel Faraday-Cage Inspired FSS Shield for Stable Resonance Performance Characteristics
摘要： In this latter, a novel Faraday cage inspired frequency selective surface (FSS) array is illustrated to patch-type periodic element. A metallic via has been used to stow the two patch conducting arrays printed on either side of the substrate. The intended application of the proposed electromagnetic (EM) structure is at microwave frequencies for improved bandwidth characteristics and stable resonance response. The structure shows a very stable resonance performance up to 60o oblique incident angle and 11.52% improvement in its fractional bandwidth. In addition, the simulation results of proposed design prove the validity of proposed structure for high microwave powers. Finally, the fabricated prototype along with experimental results of the Faraday cage array show the efficacy of proposed structural design.
关键词： Faraday cage,High power handling,Electromagnetic (EM) performance,Frequency Selective Surfaces (FSS),Substrate Integrated Waveguide (SIW)
更新于2025-09-10 09:29:36
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Gallium Oxide || Power MOSFETs and diodes
摘要： Gallium oxide-based transistors and diodes possess fundamental electronic properties that make it an ideal candidate for high-power devices. A number of these properties derive directly from the wide bandgap of Ga2O3 (Eg ? 4.85 eV) including an exceptionally high electric breakdown field (approximately 8 MV/cm). This high breakdown field allows Ga2O3-based devices to be biased at a high drain voltage (Vbreak-down ? 100 V) while maintaining a large dynamic range. Furthermore, the wide bandgap of Ga2O3 allows device operation at elevated temperature (>300°C) without degradation. In addition, Ga2O3 has a high saturation electron velocity (vsat ? 2 (cid:2) 107 cm/s), which is partially accountable for the high current density, Imax (Imax (cid:3) qnvsat, where q ? 1.6 (cid:2) 10(cid:4)19 coulomb, n ? charge density, and vs ? electron saturation velocity). Despite the relatively low thermal conductivity of Ga2O3, the rapid development of high-quality native Ga2O3 substrates lowers the overall cost of production and avoids many of the defect-related issues that have hampered GaN and SiC devices. It is expected that Ga2O3-based devices will be competitive with Si-based medium-power as well as GaN and SiC-based high-power electronic devices.
关键词： Gallium oxide,high electric breakdown field,high saturation electron velocity,high-power devices,wide bandgap
更新于2025-09-09 09:28:46
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High performance InGaN double channel high electron mobility transistors with strong coupling effect between the channels
摘要： In this paper, high performance InGaN double channel (DC) high electron mobility transistors (HEMTs) are proposed and systematically investigated. Due to the coordination of double InGaN channels, a large maximum drain current density and a distinct double-hump feature of the transconductance and frequency performance are achieved. More importantly, it is revealed that the coupling effect between the two InGaN channels is much stronger than that of the conventional GaN DC HEMTs. This characteristic leads to a remarkable enhancement in the gate voltage swing, indicating the excellent linearity of the InGaN DC HEMTs at both dc and rf conditions. Benefiting from the enhanced electron confinement in InGaN channels, the fabricated HEMTs show a low off state drain leakage current of 0.26 μA/mm and a high on/off current ratio (Ion/Ioff) of 5.1 × 106. In addition, the desirable current collapse and breakdown characteristics are also obtained. This work convincingly demonstrates the great potential and practicality of the InGaN DC HEMTs for high power and high bandwidth applications.
关键词： high power,InGaN,double channel,high electron mobility transistors,high bandwidth,coupling effect,linearity
更新于2025-09-09 09:28:46
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Metamaterial-Inspired Vacuum Electron Devices and Accelerators
摘要： Metamaterials (MTMs) are structured materials with subwavelength features that can be engineered to have some unique properties not found in nature, such as negative refractive index, reversed Doppler effect, and reversed Cherenkov radiation. Based on these novel MTMs, several important research groups have made great attempts to develop novel MTM-inspired vacuum electron devices (VEDs) and accelerators. Just as solid-state power devices are innovated by incessant emerging of new semiconductor materials, VEDs can also be inspired by MTMs to have very remarkable advantages, such as smaller size, higher power, higher efficiency, and/or larger gain relative to conventional VEDs, such as traveling-wave tubes, backward-wave oscillators, and klystrons. Similarly, relative to conventional accelerators, MTM-inspired accelerators have obvious advantages, such as smaller size and higher accelerating gradient. Furthermore, MTM-inspired devices have promising applications in areas such as radar, communication, electronic warfare, microwave heating, and imaging.
关键词： high-power microwaves,oscillators,vacuum electron devices (VEDs),electromagnetic metamaterials (MTMs),amplifiers,Accelerators
更新于2025-09-09 09:28:46