Nonlinearities of multicavity klystron amplifiers

The nonlinearities of a five-cavity klystron for wide-band operation are investigated by making use of the large signal analysis and experiments. The variations of frequency-response characteristics with respect to the input signal level, and the amplitude and phase nonlinearities are presented in detail for two typical tunings. It is shown that the nonlinearities are affected by the tuning of the intermediate cavity. The amplitude nonlinearity at saturation is about -3 to -6 dB within a frequency range of 80 MHz at the 14-GHz band. There exists some discrepancy between the calculated and measured phase nonlinearities. The nonlinear mechanisms are discussed to explain the results obtained by categorizing them into four parts. In the discussions, an emphasis is placed upon the velocity modulation of the beam by the intermediate cavity which introduces the frequency dependence into the nonlinearities.     

Large signal analysis of the multicavity klystron

The techniques developed to study large signal effects in the two-cavity klystron have been extended to determine performance of the multicavity tube. Bunching is computed as a function of excitation phase and amplitude at various gaps, tunnel lengths, beam diameter and density. Results of efficiency calculations taking into account velocity distribution within the bunch are discussed.     

Computer-aided design of the RF-cavity for a high-power S-band klystron

This article describes the computer-aided design of the RF-cavity for a S-band klystron operating at 2856?MHz. State-of-the-art electromagnetic simulation tools SUPERFISH, CST Microwave studio, HFSS and MAGIC have been used for cavity design. After finalising the geometrical details of the cavity through simulation, it has been fabricated and characterised through cold testing. Detailed results of the computer-aided simulation and cold measurements are presented in this article.     

Design considerations on a high-power VUV FEL

We explore the feasibility conditions of a high-power EEL operating in the VUV region (below 100 nm) and exploiting a coupled oscillator triplicator configuration. A high quality beam from a linac is passed through a EEL oscillator and produces laser radiation at 240 nm. The same beam is extracted and then injected into a second undulator tuned at the third harmonic of the first. The bunching produced in the oscillator allows the start up of the laser signal in the second section which operates as an amplifier. We discuss the dynamical behavior of the system and the dependence of the output power on the characteristics of the e-beam and of the oscillator. The possibility of enhancing the output power, adding a tapered section to the second undulator, is finally analyzed     

Design of beam-wave interaction based on high efficiency of a high-power broadband klystron

The paper mainly presents the design of beam-wave interaction of a C-band high-peak- power high-efficiency broadband klystron. The beam-wave interaction section is designed based on considerations of efficiency and bandwidth synthetically. As a part of beam-wave interaction section, buncher section is simulated by Particle-In-Cell （PIC） code to observe the bunching process of electron beam to achieve high conversion efficiency of electron beam and RF field. When it comes to the other part, output circuit is designed as a three-section filter by an output cavity loaded with Chebyshev filter and the cold test results are given. The beam-wave interaction is simulated by EGUN code and Ar- senal-MSU code respectively. The simulated results indicated that, the existence of power dips in the operating bandwidth is verified by Arsenal-MSU code, comparing proper results by EGUN code. Then, the method that design parameters are not adjusted except parameters of buncher cavities to remove potential power dips is described. What is more, the simulated results of electron optics system are given by EGUN code and Arsenal-MSU code respectively. The further hot test results of klystron prove that the whole design of beam-wave interaction is effective.     

A high repeatability channel-tuning system for 30-GHz band high-power klystron

A high-repeatability and wide-band channel tuning system has been developed for a 30-GHz band high-power klystron. The cavity tuner is of the choke-type and operates stably over a 1.5-GHz frequency range. To obtain satisfactory channel tuning repeatability, a feedback loop was devised in order to compensate for pulse motor rotation.     

Design considerations for the gyro-peniotron oscillator

The gyro-peniotron shows great promise as a source of microwave radiation. In this paper we investigate the stability and the non-linear saturated efficiency of a gyropeniotron oscillatro with an axis encircling beam operating at the TE₂₁₁ and the TE₃₁₁ cylindrical cavity modes. Beam and cavity parameters for stable high efficiency operation are presented from a linear theory analysis of the start-oscillation condition. Using design parameters taken from the linear analysis, the strong field non-linear emission efficiencies are studied numerically. The sensitivity of the saturated efficiency to beam axial velocity and guiding center spread is also considered. The results of our modeling indicate that high efficiency (70–90%) operation of the gyro-peniotron oscillator is possible, even with large guiding center \((\delta r_{gc_ \circ } \mathop< \limits_ \sim 0.2 - 0.4r_{L_ \circ } )\) and large axial velocity \((\delta \beta _{||} \mathop< \limits_ \sim 0.3\beta _{||_ \circ } )\) spread.     

Some considerations for reduction of noise and instability improvement in high-power crossed-field devices

The maximum potential of the high-power crossed-field devices has been restricted because of the presence of instability in these devices without any RF drive. The experimental investigation of the crossed-field instability as found from various tubes is briefly reviewed. It is believed that this instability is due to interaction of the slow cyclotron wave with the fast forward circuit wave. The theoretical work presented here refers to the interaction of both the slow and fast cyclotron waves with either of the circuit waves. The tuning characteristics of the interacting (oscillating) frequency due to slight changes in beam velocity resulting from changes in sole-to-anode voltage or magnetic field are derived. It is found that there is a good correlation between the theoretical and experimental results only for the case of interaction of the slow cyclotron wave with the fast forward circuit wave. For other interactions the tuning characteristics have opposite signs. In order to achieve a stable and less noisy operation of the device it is necessary to avoid the interaction of the cyclotron modes with the circuit wave. This limits the usable bandwidth which is plotted for different operating parameters. The electronic efficiency depending upon these operating parameters is also discussed. The problems in the gun design are reviewed. It is estimated that the conventional Kino gun may be used without any loss in bandwidth and efficiency up to frequencies in L band provided design procedures outlined in the paper are followed. For higher frequencies one has to use modified guns unless a reduction in bandwidth and efficiency can be tolerated.     

W波段连续波带状注扩展互作用速调管高频电路的设计

针对W波段速调管难以实现连续波高功率的问题,设计了一个工作在TM₃₁-2π模式的W波段连续波带状注扩展相互作用速调管（EIK）高频电路,该电路采用电压20 kV、电流0.65 A,2.5 mm×0.3 mm的带状电子注,高频系统采用五个哑铃型的五间隙谐振腔,输出系统采用对称输出波导。通过理论设计和高频结构参数优化,三维PIC仿真结果显示：在输入功率0.2 W的条件下,能够获得超过1200 W的输出功率,效率和增益分别为9.35%和37.8 dB。在高频参数敏感性和误差稳定性方面,对TM₃₁模式和TM₁₁模式进行了详细的对比分析。     

Design of DFB lasers for high-power single-mode operation

The longitudinal-mode behaviour above threshold for DFB lasers has been analysed taking into account spatial hole burning along the laser axis. As a result, the single-longitudinal-mode operating condition up to high optical output power has been made clear.     

大功率LED恒流驱动电源设计

为了驱动高功率LED,设计了一种基于隔离反激式原理的恒流驱动开关电源。该设计主要包括反激式开关电源电路的设计、开关电源变压器的选择和设计、功率因数校正电路的设计以及相关的各种保护电路的设计。综合考虑EMI和散热问题,对该电源进行了恰当的PCB设计并完成了实物制作,对该电源进行了输出测试和功率因数测试实验,实验结果表明该电源功率输出稳定,输出电压为41.8V,电流为338mA功率因数为0.86,并成功点亮了12个1 W的大功率LED。该设计对大功率LED的应用具有一定的参考价值。     

Design of birefringent filter for high-power dye lasers

A birefringent filter which is suitable for tuning dye lasers having high gain is described. Transmission and tuning characteristics for the filter are calculated. Several appropriate designs having small sidebands, a minimum number of elements, and narrow passbands are discussed.     

Design considerations for shaped-beam reflectors

A modified procedure is proposed for the design of shaped-beam reflectors in general. The procedure involves explicitly the size of the reflector as a parameter and can thus be used to check quickly the minimum size of a reflector needed for a given shaped beam. Experimental results are given for a reflector designed on this basis.     

Design considerations for acousto-optic devices

The design and fabrication of wide-band bulk acousto-optic modulators (temporal modulation) and beam deflectors (spatial modulation) are described. Optimized device parameters can be obtained systematically for given specifications of the desired modulation bandwidth, throughput efficiency and number of resolvable elements. As the device operating frequency goes beyond a few hundred megahertz, the acoustic transducer response becomes sensitive to the intermediate metal layers between the piezoelectric transducer and the acoustooptic interaction medium. Transducer bandwidth and impedance matching can be optimized using computer modeling programs. Criteria for material selection based on performance requirements and propagation loss are presented. Practical considerations for the fabrication of high performance devices and specific device parameters are discussed.     

Design considerations for high-current photodetectors

This paper outlines the design considerations for gigahertz-bandwidth, high-current p-i-n photodiodes utilizing InGaAs absorbers. The factors being investigated are photodetector intrinsic region length, intrinsic region doping density, temperature effects, illumination spot size, illumination wavelength, frequency, and illumination direction. Space-charge calculations are used to determine optimal device geometry and conditions which maximize saturation photocurrent. A thermal model is developed to study the effects of temperature on high-current photodetector performance. The thermal and space-charge model results are combined to emphasize the importance of thin intrinsic region lengths to obtain high current. Finally, a comparison between surface-illuminated p-i-n structures and waveguide structures is made to differentiate between the problems associated with achieving high current in each structure and to outline techniques to achieve maximum performance     

Design considerations for submillimeter-wave reflex klystrons

The problems facing the development of klystrons for use at submillimeter wavelengths are reviewed. Analytical formulas for reentrant cavity resonance, starting conditions, output power, and oscillation buildup are presented. This paper describes methods of calculating cavity Q-factor, output coupling, focusing potentials, electron paths, and heating effects. The scaling of output power with frequency is derived. Examples of techniques that might be used to realize a working device are presented.     

Design considerations for multi-fiber ferrule manufacturing

Fiber optic connectors are bridges linking the key elements of optical communication devices. Among them, ferrules used to position and align fibers are essential and the most critical component for fiber optic connectors. In this paper, design accuracy of ferrules will be studied. Factors affecting the fiber eccentricity during ferrule connections, including dimensions and tolerances, will be discussed and expressed in mathematical models. The 2MT ferrule was used as an example. Also, the precision plastic injection molding technique will be used to manufacture the ferrules. In order to reduce the eccentricity values for the required insertion loss, the Taguchi method is first used to simplify the optimization problems of the injection molding process. The design of experiment methodologies are then used to obtain more accurate settings for the parameters. Using these settings, ferrules with a 0.00055 mm mean eccentricity value can be obtained, and insertion losses were measured to verify the mathematical model.     

Design considerations for complementary inchworm actuators

An inchworm actuator is described, which uses complementary configurations for the two clamping sections. In one configuration, clamping and release are achieved using high and low voltages, respectively, while for the other, clamping and release are achieved using low and high voltages, respectively. The resulting inchworm actuator can be driven by a two-channel controller with the two clamps sharing the first channel and the extender piezoelectric actuator using the second channel. The paper also describes a diode-shunted delay circuit that causes unclamping to occur more slowly than clamping. It is shown that by using the delay circuit in series with each clamp, the overall force drive capability of the actuator is increased. The paper presents simulated and experimental results of clamp force versus time during the switching transient. An analysis of a generalized delay circuit having both resistive and reactive elements shows that a purely resistive design provides the better tradeoff between increased force drive capability and power loss in the delay circuit.     

Design considerations for a-Si solar cells

Amorphous Si (a-Si) is potentially an attractive material for thin-film solar cells. However, its potential for high-efficiency devices to date has not been realized. In this paper, we examine the design considerations which can be used to develop high-efficiency devices from a-Si. The design analysis takes full advantage of the flexibility in bandgap and other material properties offered by a-Si. Several structures, such as light-trapped cells, graded layer cells, and tandem junction a-Si/a-Si cells are analyzed in detail for collection efficiency, Voc, and fill factors. It is shown that using these innovative structures, realistic conversion efficiencies exceeding 10 percent can be realized in a-Si in spite of the very low diffusion lengths (∼0.1 µm). Technological considerations for achieving such structures are also discussed.     

Design considerations for high-frequency crystal oscillators

The deleterious effects of crystal shunt capacitance and series resistance on the performance of series-mode oscillators are discussed. When the parasitic capacitance across the crystal significantly modifies the transconductance of the amplifying stage the circuits can become susceptible to a parasitic second mode of oscillation above the series-resonance frequency of the crystal. A simple model that can sufficiently describe such crystal oscillator circuits was developed and used to derive simple design equations that can accurately predict the behavior of these circuits. The design equations should be especially useful for a reliable design in cases when it is not practical to use an additional inductor to compensate for the parasitic shunt capacitance of the crystal. It is shown theoretically that the inclusion of this capacitance in the feedback path reduces the total effective capacitance in the tank circuit, which is tuned to the desired overtone frequency. This creates a second mode of oscillation frequency which is higher than the desired crystal resonance frequency. The ranges of loop-gain and tank resistance values that can prevent this parasitic mode of oscillations are derived. It is also shown that the useful loop gain for the desired oscillations to start is restricted to a similar region by the crystal shunt capacitance and series resistance