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In this brief, a 400 kW-level 95-GHz gyrotron has been designed and measured. By linear analysis, TE+22.6 mode is selected as the operating mode. Through the time-dependent multimode self-consistent analysis, main mode TE+22.6 can steadily operate at the conditions: beam voltage of 51.6 kV, beam current of 24 A, beam radius of 11.75 mm, and magnetic field of 3.62 T. With the help of CST microwave studio and numerical calculation code, the single-disk vacuum window has been designed for the transmission of the main mode. The measured results show that the output power of 430 kW and the frequency of 95.3 GHz are obtained at the current of 24 A, the voltage of 51.6 kV, and the magnetic field of 3.615 T.

A graphene metamaterials based on plasmon-induced transparent has been proposed, which is composed of graphene split rings and graphene nanostrip. Split ring and nanostrip can generate resonance points at different frequencies under the excitation of terahertz waves. When these two structures are combined, two transparent windows are generated due to the destructive interference. Via tuning the Fermi energy of graphene of MaSRR, the amplitude of the first transmission peak increased from 0.64 to 0.86, and the amplitude of the second transmission peak decreased from 0.97 to 0.85. Via tuning the Fermi energy of graphene of MiSRR, the amplitude of the first transmission peak remains unchanged, and the amplitude of the second transmission peak ranges from 0 to 0.85. This study provides a good theoretical basis for the diversity of terahertz wave modulation.

Aims The activated AMP activated protein kinase (AMPK) serves as a transient protective cardiovascular kinase via preserving adenosine triphosphate (ATP) production under ischemic conditions. However, recent studies reveal that inhibition of AMPK in stroke is neuroprotection. Pigment epithelium derived factor (PEDF) is also known for the protection of ischemic cardiomyocytes. However, the relationship between PEDF and AMPK in cardiomyocytes is poorly understood. Methods and results Rat neonatal and adult left ventricular cardiomyocytes were isolated and subjected to oxygen-glucose deprivation (OGD). During OGD, PEDF significantly reduced AMPKα levels to decrease ATP production and reduced ATP expenditure both in neonatal and adult cardiomyocytes, which increased energy reserves and cell viability. Importantly, pharmacological AMPK inhibitor reduced ATP production but failed to decrease ATP expenditure, thus leading cells into death. Furthermore, AMPKα was degraded by a ubiquitin-dependent proteasomal degradation pathway, which is associated with a PEDF/PEDFR/peroxisome proliferator activated receptor γ (PPARγ) axis. Inhibition of PPARγ or proteasome disrupted the interaction of AMPKα and PPARγ, which abolished AMPKα degradation. Importantly, the decrease of AMPKα and ATP level was normalized after recovery of oxygen and glucose. Conclusions We demonstrate a novel mechanism for regulation of cardiac ATP production by PEDF involving AMPKα and PPARγ. PEDF promotes proteasomal degradation of AMPK and, subsequently, reduces ATP production. The reduction of ATP production associated with the decrease of ATP expenditure completed by PEDF increase energy reserves and reduces cell energy failure, prolonging the cell activity during OGD.

The lack of terahertz sources, especially the high-power ones, is one of the main obstacles in the developments of terahertz science and technology. A gyrotron, based on the electron cyclotron masers, is one of the most promising sources to generate high-power terahertz radiation. Therefore, a 0.42-THz gyrotron with a gradually tapered complex cavity operating at the second harmonic is designed and experimentally tested in this paper. Experimental results show that the designed gyrotron can generate high-power THz radiation of 19.2 kW at 0.42 THz with the beam voltage ${V}_{\textsf {0}}$ of 51 kV, beam current ${I}_{\textsf {0}}$ of 4.4 A and the external magnetic field ${B}_{\textsf {0}}$ of 8.03 T, corresponding to an efficiency of 8.6%. By comparison with theoretical results, it can be shown that the operating mode in the designed gyrotron is confirmed as the TE17.4 mode. At the same time, the excitation of the fundamental TE0.5 mode is also observed in the experiment when the beam current is increased to 7.3 A, where the operating frequency is 216.143 GHz. Through extensive experimental efforts, it is found that the designed gyrotron can operate stably at the desired TE17.4 mode when the beam current is in the range of 3–7 A.

Terahertz (THz) and sub-THz science and technology are very hot today. However, it is difficult to obtain high-power source of THz wave. Gyrotrons are well known as one of the most promising source for powerful THz radiation. In this paper, a 0.42-THz second harmonic gyrotron with complex cavity operating at TE17.4 is numerically simulated and designed by adopting self-consistent nonlinear theory with the first-order transmission line equations. Meanwhile, the mode competitions in the designed gyrotron have been investigated carefully by using time-dependent multimode nonlinear theory. It is proved that the operating mode can be first excited and other competing modes are well suppressed in the complex cavity. Based on these numerical simulations, the designed complex cavity gyrotron has been manufactured and measured in the Terahertz Science and Technology Research Center at the University of Electronic Science and Technology of China. The measured results show that the designed gyrotron can stably operate at TE17.4 with pulsed output power of 19.3 kW when the beam current ${I}_{{0}}$ is 4.4 A, beam voltage ${U}_{{0}}$ is 51 kV, and magnetic field ${B}_{{0}}$ is 8.03 T. The corresponding frequency and interaction efficiency are 421.645 GHz and 8.6%, respectively.

Stable operation in a single mode is an important goal of high-power gyrotron. Both multimoding and switching into unwanted modes can lead to lower efficiency. Based on the multimode, multifrequency, and time-dependent fixed field theory, a numerical code has been written for simulating the mode competition in the complex cavity gyrotron operating at the second harmonic, which is confirmed to be correct by comparison with the self-consistent simulation. With the help of the code, the mode competition in the designed complex gyrotron with the frequency of 0.42 THz is simulated by tracking several competition modes without considering ohmic losses, whose influence is roughly estimated. Through mode competition simulations, it is verified that the complex gyrotron with gradually tapered cavity has a good capability to suppress the mode competition, especially the competition from the fundamental modes. Meanwhile, the simulations show that the single mode oscillation of the desired mode TE17.4 at 150-kW level can be expected when the optimal operating condition is that the beam voltage is 50 kV, the beam current is 6 A, and the applied magnetic field is 7.98 T.

High-power terahertz gyrotrons always operate at high-order modes to avoid damage from Ohmic heating. However, the spectral densities of these modes are very high, especially when gyrotrons operate at high-order harmonics. Therefore, the self-excitation condition can be satisfied for several modes simultaneously. Correspondingly, in order to determine which mode will be excited first in the designed terahertz gyrotron, the starting currents of competing modes should be calculated more accurately to predict the operating status. In this paper, an existing linear theory is generalized to take into account the influences of the field profile, finite beam thickness, and velocity spread. Starting currents are calculated for the operating and the most dangerous competing mode in a 0.42-THz second harmonic gyrotron with a complex cavity, which is recently under development at the Terahertz Science and Technology Research Center. The calculations show that the radial and velocity spreads play a critical role in the starting current and prove that the measured output terahertz radiation in the designed device is generated from the interaction between the desired mode and the electron beam.

Gyrotron oscillators are one of promising sources to generate high power terahertz radiation. To achieve high power at high frequency, gyrotrons have to operate at high order modes to alleviate the problem of wall heating and the miniaturization of interaction structures at these frequencies. Due to high order modes, the mode spectrum is very dense and the electron beam is likely to interact with several modes. Mode competition is a major hurdle in achieving stable and efficient operation of a gyrotron at cyclotron harmonics. The gradually tapered complex cavity could suppress mode competition by locking a pair of operating modes in two single cavities. Starting from the general transmission line equations with an electron beam, self-consistent nonlinear simulations on the second harmonic complex cavity gyrotron operating at 0.42 THz are presented. The influences of the electron beam parameters on the interaction efficiency are analyzed. The experimental results show that the designed complex cavity gyrotron is operationally stable at TE 17.4 with pulse output power of 22.25 kW when the beam current is 4.8 A, beam voltage is 45 kV, and applied magnetic field is 8.185 T. The corresponding frequency and interaction efficiency are 421.60 GHz and 10.27%, respectively.

The problem of mode competition can present a major hurdle for gyrotron to achieve stable and efficient operation, especially when the gyrotron operates at electron cyclotron harmonics. Therefore, an effective theoretical investigation of the mode competition is an essential first step to the implementation of gyrotron. In this paper, the nonlinear dynamics of the mode competition in the terahertz gyrotron operating at high-order mode are studied using a multifrequency time-dependent model. Based on the model, the simulations of mode competition in the designed gyrotron are presented by the corresponding code. The influence of the velocity spread on the mode competition is also studied. The simulations tracking five competing modes show that stable excitation of the second harmonic oscillation can be realized with a proper choice of the operation parameters. The results show that a single-mode second harmonic radiation with a power of over 120 kW at a frequency of 0.4 THz could be achieved.

A double anode magnetron injection gun (MIG) for a 0.42 THz second harmonic gyrotron has been presented in this paper. Through design, simulation and optimization by the particle-in-cell code, a double-anode electron gun with maximum transverse velocity spread of 3.19 % is obtained, the beam acceleration voltage is 50 kV, operating current is 5.5 A and the ratio of the transverse velocity to the axial velocity is equal to 1.4. A comprehensive analysis of MIG for 0.42 THz second harmonic gyrotron is presented, and the designed electron gun well satisfies the requirement of the 0.42 THz gyrotron.

In this paper, the results of theoretical study on a 0.4-THz second harmonic gyrotron operating at TE19.3 are presented. A gradually tapered cavity is adopted to alleviate the problem of parasitic mode competition. It is proved that the amplitudes of spurious modes in the gradually tapered cavity could be kept lower than that in the line-joint cavity, especially that in the line-joint cavity with large angle. Based on the self-consistent nonlinear theory, a code is written to simulate the process of beam–wave interaction. Through optimizing the operating parameters, the beam–wave interaction efficiency can reach 35% and an output power of 100 kW can be obtained. In addition, the mode competition in the designed gyrotron is studied using multifrequency time-dependent nonlinear theory. Simulations tracking five competition modes show that stable excitation of the desired operating mode TE19.3 at 100 kW level can be realized with proper choice of operating parameters.

Confocal gyrotron traveling-wave tube (gyro-TWT) is a novel gyrotron amplifier capable of operating in higher order modes while generating high power at the same time. So far, confocal gyro-TWT has been studied by MIT both in theory and experiment at 140 GHz. In this paper, a center frequency of 170-GHz $\mathrm{TE}_{06}$ -mode confocal gyro-TWT is designed theoretically, and it features high power and broadband capabilities. Theoretical investigation predicts that, when the magnetic injection gun is optimized to generate an electron beam of 65 kV, current of 7 A, with a pitch factor of 1.2, this gyro-TWT is of an excellent performance. At a given operating magnetic field of 6.11 T, with an input power of 10 W, a saturated gain of at least 30 dB, 3-dB bandwidth of over 4 GHz and highest efficiency of 17.1% are achieved.

Confocal gyrotron traveling wave tube (gyro-TWT) is a novel gyrotron amplifier capable of operating in higher order modes while generating high power at the same time. Confocal gyro-TWT suppresses lower-order modes at the cost of reduction of efficiency. According to the characteristics of confocal system, in this paper, we theoretically design a special magnetron injection gun (MIG) for a 170 GHz confocal gyro-TWT, and then compare it with the traditional MIG. The efficiency is found to be as high as 33 %, deservedly higher than the traditional less than 10 %. The output power increases trebly accordingly.

The mode competition and beam wave interaction in a gradually tapered cavity are studied for achieving high efficiency of a 0.6-THz second harmonic (SH) gyrotron. In order to obtain high power and stable radiation, the TE32,5 mode is selected as the operating mode of the desired gyrotron to realize a single-mode oscillation. The issues of studying the high-order mode gyrotron are solved effectively by transforming the generalized telegraphist's equations. The efficiency and the output power of the gyrotron under different conditions have been calculated by the code, which is based on the transformed equations. The results show that a single-mode SH radiation with a power of over 100 kW at frequency of 0.6 THz could be achieved.

In this paper, a coaxial resonator with inner-outer corrugation is studied. By the surface impedance theory, its eigenequation is derived; by the energy balance equation, its ohmic quality factor is obtained. Research shows that for a coaxial resonator with outer, inner, and inner-outer corrugation, slot depth can influence eigenvalue, ohmic quality factor, and wall loading loss in comparison with coaxial smoothing resonator; in the region of eigencurve with positive slope, ohmic quality factor, and wall loading loss of outer slot bottom attain the minimum. However, wall loading loss of inner slot bottom attains the maximum and wall loading loss of inner slot bottom is larger than one of outer slot bottom. These results can help us to research mode selection and mode competition of coaxial resonator with inner-outer corrugation.

In the paper, according to Eigen equation of coaxial resonator with inner-outer corrugation, its Eigen value is researched by numerical calculation method. Results find that outer slot width and outer slot depth on the outer conductor have greater influence on characteristic value on the whole, respectively. Slope angles of input and output part of outer conductor and of inner conductor have influence on Eigen value in local region of the resonator. However, inner slot width and depth on the inner conductor have slightly influence on Eigen value. These results can help us to research the rest properties of coaxial resonator with inner-outer corrugation.

The open sides of confocal waveguide diffract the spurious modes and operating mode at the same time. The operating mode must be converted to Gaussian mode to avoid transmission loss during a long transmission length. The transmission loss was analyzed and a simple output coupler was designed to convert the confocal TE 06 mode to circular TE 03 mode in this paper.

The gyrotron has been demonstrated to be an efficient, high power source of terahertz radiation. However, one of the main obstacles in achieving stable, efficient operation at the cyclotron harmonics in a gyrotron is mode competition with lower harmonic modes. Therefore a theoretical investigation of mode competition is an essential first step to the implementation of gyrotron. In this article, the nonlinear dynamics of mode competition in 0.4 THz gyrotron with gradually tapered complex cavity are studied by using multifrequency, time-dependent theory. The results show that the operating modes TE 17.3 –TE 17.4 can be stably excited and the output power can reach over 130 kW.

A double anode magnetron injected gun (MIG) for a terahertz (THz) band cyclotron oscillation tube has been presented in this paper. Through design, simulation and optimization by the particle-in-cell (PIC) code, a double-anode electron gun with trans-velocity spread of 3.19% is obtained, and the ratio of the transverse velocity to the axial velocity is equal to 1.4. The designed electron gun well satisfies the requirement of the 0.4 THz gyrotron.

Recently, a 0.42 THz second-harmonic gyrotron with complex cavity has been investigated and measured in the Terahertz Research Center. The experimental results show that the designed gyrotron can operate stably at the candidate mode TE−17.4 with the pulsed power of 19.3 kW, corresponding to an efficiency of 8.6%. However, the measured output power and efficiency are much lower than the theoretical values. In this paper, the influences of beam quality and Ohmic loss on the beam-wave interaction in the designed complex-cavity gyrotron are analyzed explicitly by a nonlinear, time-dependent, multi-mode code. The numerical simulations show that in the low-beam-voltage region, the calculated powers perfectly fit with the experimental results when the electron beam width is 0.195 mm, the electron velocity spread is 6% and the Ohmic quality factor of TE−17.4 is about 75000. Meanwhile it is also found that competing modes are well suppressed although considering the beam quality and Ohmic loss, which reproduces the experimental observation of the high-power single-mode oscillation of the TE−17.4 mode as the design mode.

In this paper, the nonlinear dynamics of mode competition in the complex cavity gyrotron are studied by using multi-frequency, time-dependent theory with the cold-cavity longitudinal profile approximation. Based on the theory, a code is written to simulate the mode competition in the gradually tapered complex cavity gyrotron operating at second harmonic oscillation. The simulations tracking seven competition modes show that single mode oscillation of the desired mode TE17.4 at 150 kW level can be expected with proper choice of operating parameters. Through studying on mode competition, it is proved that the complex cavity has a good capability for suppressing the mode competition. Meanwhile, it is found that TE17.3 could be excited in the first cavity as a competition mode when the gyrotron operating at large beam current, which leads to that TE17.3 and TE17.4 with different frequencies can coexist stably in the complex cavity gyrotron with very close amplitudes. Thus, the complex cavity might be used for...

In this paper, a coaxial resonator with longitudinal inner-outer corrugation is introduced. Its eigen-equation and expression of ohmic losses are derived. Ohmic losses in the cavity are investigated. Results show that ohmic losses in the outer and inner conductors share a similar variation trend, while the former is larger than the later. What's more, changes of the inner and outer slot depth and width induce different variations of ohmic losses on the surface of the inner and outer conductors.