LARGE-SIGNAL SIMULATIONS OF A GYROTRON TRAVELING-WAVE AMPLIFIER WITH A MODE-SELECTIVE INTERACTION CIRCUIT

A self-consistent nonlinear theory is used to analyze the saturated performances of a Ka-band gyrotron traveling wave amplifier (gyro-TWA) operating at the fundamental with a mode-selective interaction circuit involving a tapered vane-slot mode converter. The amplifier is predicted to generate 140 kW saturated output power with 33.3% efficiency, a saturated gain of 33dB, and a 3dB bandwidth of 2.7 GHz (8%) for a 70 kV, 6A electron beam with a velocity ratio of 1.0 and an axial velocity spread of 5%.     

分布损耗对回旋行波放大器稳定性的影响

基于电磁模式的色散方程和回旋管非线性理论,研究了损耗层厚度对回旋行波放大器注-波互作用的影响.结果表明,合理选择损耗层电导率和厚度能够让期待的工作模式TE₀₁衰减较小,而对应的竞争模式TE₂₁因损耗很大而更难以起振,随厚度的增加,放大带宽从两边向中间收缩变窄,频带中间部分的输出功率会上升,曲线更加平坦,从而达到改善互作用稳定性的目的. 关键词： 回旋行波放大器 起振长度 起振频率 饱和功率     

A High-Gain, 28GHz, 200kW Gyroklystron Amplifier

A design study of a high efficiency/gain gyroklystron amplifier is performed to demonstrate amplified radiation power of 200kW operating at 28GHz. A key design feature of the present gyroklystron amplifier is that the amplifier is designed to be high gain so that it can be saturated by a low power solid state power amplifier. A non-linear, time-dependent, large signal numerical code is used to predict tube performance. Simulations predict that a stable amplifier radiation power of 214kW is produced with a saturated gain of 54dB, an electronic efficiency of 37%, and a frequency bandwidth of 0.3% from a five-cavity gyroklystron amplifier. The amplifier gain is found to be very sensitive to a beam velocity spread.     

回旋行波放大器输出端反射对注-波互作用的影响

基于回旋行波放大器的非线性自洽理论,研究渐变输出端反射对回旋行波放大器注-波互作用的影响.数值模拟结果表明,对于Ka波段TE₀₁模基波工作回旋行波放大器,渐变输出端渐变角的变化以及互作用长度的改变将导致不同的反射系数幅度和相位,从而影响注-波互作用过程,改变功率演化过程.在输出饱和功率不变的情况下,合理选择输出渐变角,可能可以减小注-波互作用长度,展宽互作用频带. 关键词： 回旋行波放大器 注-波互作用 反射系数     

Influence of Reflections of the Output Port on Beam-wave Interaction in Gyrotron Traveling Wave Amplifier

Based on the nonlinear self-consistent theory of gyrotron traveling wave amplifier (gyro-TWA), the influence of the reflections of the output port with the taper on the beam-wave interaction in the gyro-TWA is studied. The simulation results show that the reflections have great effects on the TE₀₁ mode gyro-TWA operating at the fundamental. The influence of the taper angle and the interaction length on the beam-wave interaction and the power profile is discussed and the corresponding physical mechanism is analyzed. The saturated output power keeps same approximately with the increase of the taper angle in the presence of reflection while the saturated gain decreases obviously.     

Preliminary Design of a Harmonic-doubling Gyrotron Traveling Wave Amplifier

This study proposes a Ka-band harmonic-doubling gyrotron traveling-wave amplifier (gyro- TWT), using distributed wall losses in the input stage and mode-selective interaction circuit in the output stage, to improve the stability of the amplification. Based on a large signal simulation code, a saturated peak power of 163 kW with an efficiency of 15.5%, a gain of 31.1 dB, and a 3 dB bandwidth of 0.9 GHz is predicted for the gyro-TWT driven by 70 kV, 15 A electron beam with a velocity ratio of 1.2 and velocity spread 5% at 33.2 GHz.     

Large-signal characteristics of a wide-band dielectric-loadedgyro-TWT amplifier

The bandwidth of a gyrotron traveling wave amplifier (gyro-TWT) has been significantly increased by partially filling the interaction waveguide with dielectric to reduce the circuit's dispersion. The proof-of-principle experiment was designed for X-band, and employs the fundamental mode of rectangular waveguide loaded with dielectric slabs along the narrow sidewalls. The amplifier yields a peak output power of 55 kW with 11% efficiency, 27 dB saturated gain, and an unprecedented untapered gyro-TWT constant-drive bandwidth of 11% and saturated bandwidth exceeding 14%. The single-stage amplifier is completely zero-drive stable. The 95-kV 5-A electron beam was produced by a single-anode magnetron injection gun with p_⊥/υ_z=0.6, as determined by the EGUN code, and Δυ_z/υ_z=4%, determined as the best fit to the gyro-TWT large-signal simulation data. Simulation studies predict that by lowering the velocity spread to Δυ _z/υ_z=2%, the amplifier performance will be further enhanced to a constant-drive bandwidth of 20% with 15% efficiency     

Design of a 50 kW, wideband Ka-band slow wave cyclotron amplifier

A two-stage slow wave cyclotron amplifier is investigated to demonstrate a high power, stable, and broad Ka-band radiation source, operating at a low beam power (~60 kV, ~5 amps) and a low magnetic field (~7 kG). A linear theory predicts that the second harmonic gyro-BWO is competing in the amplifier and can be stabilized by inserting a sever in the interaction circuit. A slow-time-scale non-linear code, with a sever included, predicts a saturated gain of 24-28 dB, an efficiency of 15-17%, and an instantaneous bandwidth of 15-20% at a beam axial velocity spread of 2%. A broadband RF coupler, a mode converter, and a RF vacuum window are designed by the use of a 3D electromagnetic, finite element code. Measured RF characteristics are in good agreement with predictions     

回旋行波放大器输出端反射对其稳定性的影响

 基于回旋行波放大器的线性理论和反射边界条件,建立了渐变输出端存在反射时回旋行波放大器模型,分析了TE₀₁圆电模基波回旋行波放大器输出端反射对其增益、返波起振长度、返波起振电流和返波起振频率的影响。结果表明,随着反射增强,线性增益降低,返波起振长度和起振电流减小,返波起振频率的变化较小;反射增强将在一定程度内影响放大器的稳定性。     

Theory, Design, and Operation of Large-Orbit High-Harmonic Gyroklystron Amplifiers

The high-harmonic gyroklystron is a compact RF amplifier which relies on the synchronous interaction between large-orbit axis-encircling electrons and high-order azimuthal cylindrical cavity TEn11 modes. Because of this unique structure, it offers the promise of moderate- to high-millimeter-wave output power. Experimental results for a fifth-harmonic two-cavity device are compared to both small-signal analytic theory and large-signal numerical calculations which assess gain, bandwidth, sensitivity to longitudinal velocity spread, self-oscillation, and saturation characteristics. Principal theoretical results include the transition to infinite gain as the start-oscillation current threshold is reached as well as the demonstration of the insensitivity of the small-signal gain to parallel velocity spread. The required high-energy rotating electron beam is provided through gyroresonant RF acceleration. To date, over 20 dB of small-signal gain has been achieved at 11.3 GHz in a 1.3-kG magnetic field. The design of a four-cavity configuration is also presented along with simulation of its gain, bandwidth, amplitude modulation (AM) and phase modulation (PM) sensitivity, dependence upon guiding-center spread, and large-signal saturation characteristics. This device has been constructed and initial tests have yielded a gain of 30 dB. Gain in excess of 50 dB is predicted.     

Stable high-power TE01 gyro-TWT amplifiers

The stability of high power gyro-TWT amplifiers operating in the low-loss TE₀₁ mode of cylindrical waveguide has been studied, Linear theory has been used to determine the threshold start-oscillation beam current for absolute instability in the operating mode and the critical section lengths for the dominant gyro-BWO interactions occurring at various cyclotron harmonics in other waveguide modes. The performance of the amplifier was evaluated with a nonlinear, self-consistent slow-timescale simulation code. Utilizing interaction sections whose lengths are less than the threshold start-oscillation length and are separated by attenuating severs for isolation, two stable three-section devices have been designed which are predicted to yield: (1) a peak output power of 230 kW at 35 GHz with an efficiency of 23%, a saturated gain of 46 dB and a constant-drive bandwidth of 6% for a 100 kV, 10 A electron beam with an α=ν_⊥ /ν_z =1.0 and an axial velocity spread Δν_z/ν_z=5% and (2) 105 kW at 94 GHz with 21% efficiency, 45 dB saturated gain and 5% constant-drive bandwidth for a similar 5 A electron beam. In addition, the design of the 0 dB input/output couplers and the MIG electron gun are given. Due to the low loss of the TE₀₁ mode, both of these amplifiers can be operated continuously     

倍频谐波回旋行波放大器的研究

 通过研究倍频谐波回旋行波放大器中电子束在调制区和漂移区中的群聚与在辐射区中的辐射,给出了器件各部分的最佳参数;同时在均匀波导管和引导场的情况下,运用低速率比的电子束获得了宽带输出。当电子束的电压为130kV、电流为20A、速率比为0.8以及纵向速度散度为1%时,模拟得到器件的饱和带宽至少可达到10%,峰值功率和增益分别为290k W和50dB,常数驱动带宽约9%。     

Nonlinear Analysis of Coaxial Gyro-Travelling-Wave-Tube Amplifier

A set of nonlinear self-consistent equations in the electron guiding center coordinates is derived for the study of the behavior of the coaxial gyro-travelling-wave-tube (gyro-TWT) amplifier. It is found that the input signal grows faster and gets saturated earlier with the increasing of b/a (ratio of the inner to outer radius). Using an electron beam of 90kV, 10A and velocity ratio of 1.0 with 3% axial velocity spread, 275kW peak output power is obtained by calculation over the frequency range of 31.22–33.52GHz, the gain, efficiency and bandwidth are 47.4dB, 30.5% and 7.5%, respectively.     

High-gain wide-band gyrotron traveling wave amplifier with a helically corrugated waveguide

First bandwidth measurements of a novel gyrotron amplifier are presented. The coupling between the second harmonic cyclotron mode of a gyrating electron beam and the radiation field occurred in the region of near infinite phase velocity over a broad bandwidth by using a cylindrical waveguide with a helical corrugation on its internal surface. With a beam energy of 185 keV, the amplifier achieved a maximum output power of 1.1 MW, saturated gain of 37 dB, linear gain of 47 dB, saturated bandwidth of 8.4 to 10.4 GHz ( 21% relative bandwidth), and an efficiency of 29%, in good agreement with theory.     

同轴回旋行波放大器的理论和数值研究

 给出了一组描述同轴回旋行波放大器中波束相互作用的非线性自洽方程组，对该放大器的运行特性进行了研究。得到：在小信号区，辐射场的增益随同轴波导的内外半径比b/a的增加而增加，达到饱和时的辐射功率仅略有下降；内外导体管壁上的功率损耗密度随b/a的增加而减小。采用电压为90kV，电流为10A，纵向速度零散度为3%，速率比为1的电子束，在34.26～36.78GHz的频率范围内，计算得到了峰值功率约230kW的微波输出，相应的增益和效率分别为46.6dB和25.5%，带宽为7%，内外导体管壁上功率的最大损耗分别为80和56W/cm²。     

Highly efficient short length Bismuth-based erbium-doped fiber amplifier

An efficient 21 cm Bismuth-based erbium doped fiber amplifier (Bi-EDFA) operating in both C- and L-band wavelength regions is proposed and demonstrated. The proposed Bi-EDFA uses the gain medium with an erbium ion concentration of 6300 ppm in conjunction with a double-pass configuration. Compared to conventional silica-based erbium-doped fiber amplifiers (Si-EDFAs) with the same amount of Erbium ions, the Bi-EDFA provides a higher attainable gain as well as a greater amplification bandwidth ranging from 1525 to 1620 nm. The proposed Bi-EDFA achieved a flat-gain of around 23 dB with gain variation of ±3.5 dB within the wavelength region from 1530 to 1565 nm at the maximum pump power of 150 mW. The corresponding noise figures are obtained at an average of 6 dB.     

Self-Consistent Nonlinear Simulation of a Severed Slotted Gyro-TWT

The behavior of a two-stage slotted Gyro-TWT amplifier is evaluated with a self-consistent nonlinear slow-timescale simulation code. The effects of the sever position and the lengths of the first section, sever, and the second section on beam-wave interaction are discussed in this paper. And the influences of the magnetic field and the electron beam's velocity spread on efficiency, gain and bandwidth are also simulated and discussed in detail. The electron beam we employ encircles around the axis of the wave guide.     

170GHz兆瓦级同轴回旋振荡管的分析计算

回旋管是最有希望应用于正在实施的国际热核实验反应堆计划的微波源器件,然而研究设计符合要求的回旋管还存在很多困难需要解决.对170 GHz兆瓦级光滑同轴回旋管的注-波互作用进行了研究.选取模式谱相对稀疏的TE31,12作为工作模式,利用Matlab编制源程序,计算了同轴回旋管的注-波耦合系数、起振电流.在考虑电子速度零散、腔壁电阻率和单模近似的基础上,对光滑同轴谐振腔的优化设计和注-波互作用进行了仿真,给出了磁场、电压、电流和内导体倾角等参量与回旋管效率的关系.结果表明,电压和磁场对回旋管效率影响较大,电子速度零散对回旋管效率影响较小,因而可降低电子枪的设计要求.此外,优化内导体倾角和同轴谐振腔结构参数可提高注-波互作用效率,降低电子速度零散对互作用效率的影响,获得了约50%的电子效率及1.7 MW输出功率.     

Gain-clamped S-band discrete Raman amplifier

We demonstrate the advantages of an optically gain-clamped S-band discrete Raman amplifier: low gain variation over a large input dynamic range, effective suppression of Raman transients, and amplifier instability in the strong-pump-weak-signal configuration. We further investigate experimentally the operating conditions necessary for effective gain clamping and demonstrate gain flattening over 30 nm of bandwidth. Thus a gain-clamped discrete Raman amplifier shows promise for practical deployment.     

Influences of finite gain bandwidth on pulse propagating in parabolic fiber amplifiers with distributed gain profiles

The evolutions of the pulses propagating in decreasing and increasing gain distributed fiber amplifiers with finite gain bandwidths are investigated by simulating with the nonlinear Schrödinger equation. The results show that the parabolic pulse propagations in both the decreasing and the increasing gain amplifiers are restricted by the finite gain bandwidth. For a given input pulse, by choosing small initial gain coefficient and gain variation rate, the whole gain for the pulse amplification limited by the gain bandwidth may be higher, which is helpful to the enhancement of the output linearly chirped pulse energy. Compared to the decreasing gain distributed fiber amplifier, the increasing gain distributed amplifier may be more conducive to suppress the pulse spectral broadening and increase the critical amplifier length for achieving a larger output linearly chirped pulse energy.