Performance and pulse shortening effects in a 200-kVPASOTRONTM HPM source

The PASOTRON^TM is a unique, high-power microwave source that uses a long-pulse (⩽100 μs) plasma-cathode electron-gun and plasma-filled slow-wave structure (SWS) to produce high-energy microwave pulses. The device utilizes no externally-produced magnetic fields; relying on a beam-generated plasma channel in the SWS to transport the beam. Peak powers of up to 5 MW were previously reported in C-band using a rippled-wall waveguide SWS. Scaling experiments indicated that increasing the beam voltage above the 90 kV C-band operation produces significantly higher peak powers. We report results from an L-band PASOTRON^TM BWO designed to operate at 200 kV. The plasma-cathode E-gun built for this device generated beams with voltages of up to 225 kV and currents in excess of 1 kA for pulse lengths of up to 200 μs. The L-band PASOTRON^TM BWO produced 10-20 MW of peak power in the TM₀₁ mode, which was converted in the output to a TE₁₁ mode with fixed polarization. The PASOTRON ^TM also directly produced TE-mode radiation in the 5-10 MW power range with a rotating output polarization, the rate of which can be controlled externally. The peak power and poise width was limited by the stability of the plasma channel at high peak powers and excessive plasma generation in the SWS during the long pulse length     

X波段GW级长脉冲高功率微波源的设计与实验

通过理论分析指出,单模相对论返波振荡器内的平均场强正比于其工作频率,工作在高频段难以实现长脉冲运行。采用电磁场仿真方法,比较了X波段单模和过模慢波结构的场分布特点,结果表明:增加过模比能有效减小慢波结构表面的射频场强,但由于场分布变化导致场强的减小与过模比的增加相比并不显著。利用过模比约为3的慢波结构设计了一种X波段长脉冲高功率微波源。实验中,在单次运行条件下,输出微波功率达到2 GW、脉宽80 ns;在20 Hz重复频率运行条件下,输出微波功率达到1.2 GW、脉宽100 ns。器件产生的微波频率为9.38 GHz,主模为TM01,效率约24%。微波窗口和慢波结构表面的射频击穿是目前实验中限制微波功率和脉宽增加的关键因素。     

Studies of relativistic backward-wave oscillator operation in thecross-excitation regime

We first reported the operation of a relativistic backward-wave oscillator (BWO) in the so-called cross-excitation regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, resulted from the use of a particularly shallow rippled-wall waveguide [slow wave structure (SWS)] that was installed in an experiment to diagnose pulse shortening in a long-pulse electron beam-driven high-power microwave (HPM) source. This SWS was necessary to accommodate laser interferometry measurements along the SWS during the course of microwave generation. Since those early experiments, we have studied this regime in greater detail using two different SWS lengths. We have invoked time-frequency analysis, the smoothed-pseudo Wigner-Ville distribution in particular, to interpret the heterodyned signals of the radiated power measurements. These recent results are consistent with earlier theoretical predictions for the onset and voltage scaling for this instability. This paper presents data for a relativistic BWO operating in the single-frequency regime for two axial modes, operating in the cross-excitation regime, and discusses the interpretation of the data, as well as the methodology used for its analysis. Although operation in the cross-excitation regime is typically avoided due to its poorer efficiency, it may prove useful for future HPM effects studies     

Efficiency enhancement in high power backward-wave oscillators

High power microwave (HPM) sources based on the backward-wave oscillator (BWO) have been investigated for the past two decades primarily because of their potential for very high efficiency (15 to 40%) operation. Several different effects have been proposed to explain this high efficiency compared to conventional BWOs. One of the major contributors to the high efficiency of the plasma-filled Pasotron HPM BWO source is the presence of optimally phased end reflections. The Pasotron uses a long-pulse (⩾100 μs) plasma-cathode electron-gun and plasma filled slow-wave structure to produce microwave pulses in the range of 1 to 10 MW without the use of externally produced magnetic fields. The efficiency of the Pasotron can be enhanced by up to a factor of two when the device is configured as a standing-wave oscillator in which properly phased reflections from the downstream collector end of the finite length SWS constructively interfere with the fundamental backward-wave modes and improve the coupling of the beam to the circuit. Operation in this configuration increases the efficiency up to 30% but causes the frequency to vary in discrete steps and the output power to change strongly with beam parameters and oscillation frequency     

高功率微波窗内外表面闪络击穿流体模拟研究

建立理论模型,将电磁场时域有限差分方法与等离子体流体模型结合,编制一维电磁场与等离子流体耦合程序,数值研究了3 GHz高功率微波窗内外表面闪络击穿的不同物理过程.研究结果表明:外表面闪络击穿中,输出微波脉宽缩短(未完全截止),窗体前均方根场强呈驻波分布,波节与波腹位置不变,窗体外表面形成有一层高密(约10~(21)·m~(-3)量级)极薄(约mm量级)等离子体(扩散缓慢),入射波可部分透过该薄层等离子体,脉宽缩短主要源于等离子体吸收效应;降低初始等离子体密度、厚度、入射波场强及缩短入射波脉宽等方式,可不同程度地改善输出脉宽缩短效应.内表面闪络击穿中,窗体前均方根场强亦出现驻波分布f但波节与波腹位置随时间变化),等离子体向波源方向运动;强释气下,输出脉宽缩短(未完全截止),形成多丝状高密(约10~(21)·m~(-3)量级)极薄(约mm量级)等离子体区域(扩散缓慢),间距1/4微波波长,脉宽缩短主要源于等离子体吸收效应;弱释气、低场强下,脉宽缩短有所改善(但最终截止),形成多带状致密(约10~(18)·m~(-3)量级)略厚(mm-cm量级)等离子体区域(扩散较快),间距1/4波长,脉宽缩短主要源于等离子体吸收效应;弱释气、高场强下,脉宽缩短严重(很快截止),形成块状高密(约10~(21)·m~(-3)量级)较厚(约cm量级)等离子体区域(扩散迅速),脉宽缩短主要源于等离子体反射效应.     

X波段高功率宽带选模定向耦合器

过模圆波导在提高功率容量的同时,不可避免地会造成微波源中同时存在多种模式。为了监测X波段长脉冲高功率微波源TM₀₁模的输出功率和频谱,采用CST软件仿真设计了X波段高功率宽带选模定向耦合器,在耦合TM₀₁模的同时可实现对TM₀₂和TE₁₁模的抑制。波导腔体及耦合孔的尺寸以小孔耦合理论和相位叠加原理为基础并结合切比雪夫分布函数计算确定。仿真结果表明:该高功率宽带选模定向耦合器在9.0~9.8 GHz的带宽范围内,耦合度为(-59.08±1) dB,定向性大于30 dB,对TE₁₁模的抑制度大于15 dB,对TM₀₂模的抑制度大于30 dB,功率容量大于2.5 GW。     

Polarization control of microwave emission from high powerrectangular cross-section gyrotron devices

Results are summarized of experiments on a gyrotron utilizing a rectangular-cross-section (RCS) cavity region. The major issue under investigation is polarization control of microwave emission as a function of magnetic field. The electron beam driver is the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=0.8 MV, I_diode=1-10 kA, I_tube=0.1=0.5 kA, and t_e-beam=0.4-1.0 μs. The annular e-beam is spun up into an axis-encircling beam by passing it through a magnetic cusp prior to entering the RCS interaction cavity. Experimental results show a high degree of polarization in either of two orthogonal modes as a function of cavity fields. The RCS gyrotron produced peak powers of 14 MW in one polarization (TE₁₀) and 6 MW in the cross-polarized mode (TE ₀₁). Electronic efficiencies for this device reached as high as 8% with transverse efficiency of 16%. Experimental results on the beam alpha (α=V_⊥/V_∥) diagnostics, where alpha is the ratio of the e-beam's transverse velocity to its parallel velocity, agree well with the single electron trajectory code. MAGIC code results are in qualitative agreement with microwave measurements. Microwave emission shifts from the dominant fundamental mode polarization (TE₁₀□ ), to the next higher order mode polarization (TE₀₁□) as the solenoid magnetic field is raised from 1.4-1.9 kGauss. Frequency measurements using heterodyne mixers support mode identification as well as MAGIC code simulations     

一种X波段过模高效率相对论返波管

设计了一种X波段过模高效率相对论返波管(RBWO),主要结构包括双谐振腔反射器、7周期梯形慢波结构与提取腔。该器件慢波结构的过模比为2.6,电子束与结构波TM₀₁模的近π模相互作用,在慢波结构区域束波作用产生的TM₀₁模表面波主要转化为TM₀₂模的体波,其输出微波的模式主要为TM₀₂模,占比为81%,其余为TM₀₁模。提出一种过模条件下谐振腔反射器的设计思路,结合模式匹配法,优化得到了一种双谐振腔反射器结构,其对TM₀₁模与TM₀₂模的反射系数均大于0.99,可实现过模条件下RBWO慢波结构与二极管区的良好隔离; 同时双谐振腔反射器两个谐振腔中的纵向电场可以对电子束进行充分的预调制,将促进慢波结构区域的束波作用,有利于提升效率。通过在慢波结构后端加入提取腔,进一步提升了转换效率。PIC仿真中, 在二极管电压900 kV,电流14.3 kA,得到了6.6 GW的输出功率,转换效率约51%。     

双路脉冲输出结构理论设计与仿真

基于单台脉冲功率驱动源同时驱动两个微波器件产生双频高功率微波的构想,设计了一种双路短脉冲输出结构,其接于主开关后,能够将主开关产生的高压纳秒脉冲传输至高功率微波产生器。两路脉冲由同一脉冲源产生,具有很好的一致性。对双路输出结构脉冲传输过程进行了建模仿真,研究了传输线阻抗、输入脉冲前沿等电学参数对输出波形质量的影响规律,并完成了绝缘风险分析及结构优化。经评估,在前沿4～8 ns的准方波输入脉冲下,双路脉冲输出线的输出波形质量与单路传输线相当,其过冲振荡均小于20%、平顶振荡均小于1%,且能满足绝缘要求。     

0.34 THz大功率过模表面波振荡器研究

论文对0.34 THz大功率过模表面波振荡器进行了模拟设计和初步实验研究. 针对高过模比(D/λ ≈ 6.8)慢波结构, 根据小信号理论选择了合适的慢波结构尺寸和电子束距壁距离, 实现了器件在表面波TM₀₁模的π点附近谐振. 根据PIC模拟结果, 表面波振荡器可以实现频率和功率分别为0.34 THz和22.8 MW的太赫兹波输出. 采用微细电火花加工技术完成了不锈钢慢波结构的一体化精细加工, 并基于小型化脉冲功率驱动源搭建了实验装置. 初步的实验结果表明, 在电子束电压和电流分别约为420 kV和3.1 kA时, 0.34 THz大功率过模表面波振荡器输出脉冲的频率范围为0.319–0.349 THz, 辐射功率不小于250 kW, 脉宽约为2 ns. 最后分析讨论了实验输出功率与模拟结果相差较大的原因, 为表面波振荡器的性能改善奠定了基础.     

锁频锁相的高功率微波器件技术研究

综述了中国工程物理研究院应用电子学研究所锁频锁相的高功率微波器件最新研究成果,主要包括稳频稳相的相对论速调管放大器和注入锁相的相对论返波管振荡器.针对高功率长脉冲相对论速调管研究中遇到的问题,介绍了该放大器的束波互作用特点、杂频振荡抑制、脉冲缩短、高频段高功率运行、高增益等物理、设计与实验中的关键技术研究概况,使其功率、相位稳定性、增益等性能有了显著提高,S波段环形单注相对论速调管实现了高功率稳相输出,重频25 Hz运行时输出功率大于1 GW,脉宽大于150 ns、相位波动18°,高增益运行时在注入微波功率数kW条件下也实现类似功率和相位水平;采用同轴多注器件结构,突破了速调管高频段运行条件下高效率电子束引入和高功率束波转换技术等难题,使X波段相对论速调管在注入功率30 kW条件下实现了功率大于1 GW的放大输出,效率为34%,相位波动为15°.在掌握相对论返波管技术的基础上,利用返波管的高效率和结构紧凑的优点,开展了注入调制电子束锁相的相对论返波管研究,采用百kW级的种子微波实现了对GW量级输出微波的相位锁定.该研究结果对功率合成、粒子加速和多功能雷达等技术具有重要的推动作用.     

Evolution of pulse shortening research in narrow band, high powermicrowave sources

The achievements resulting from the application of advanced pulsed power to the generation of high power microwaves (HPM) have included the generation of multi-gigawatt pulses of RF energy. The power achievable is orders of magnitude greater than conventional microwave sources can generate. However, the introduction of the HPM technology into logical applications has been limited to date due to the phenomenon of pulse shortening in which the RF pulse terminates before the pulse power source used to produce it. Conventional microwave tubes can generate a few to 10 MW of power with pulsewidths of many microseconds when required. High power microwave sources can produce gigawatts of power, but only for relatively short pulsewidths, typically tens to hundreds of nanoseconds. An international effort during the past few years has generated important new discoveries toward the elimination of pulse shortening. Some of the new techniques have the potential for helping the conventional tube industry as well as being practical for high power microwave sources. This paper reviews the pulse shortening problem, its causes, and the worldwide scope and direction of research conducted to date to resolve it. The paper also discusses the potential remedies for the problem and recommends a course of research to further progress on the issue     

微波输出窗内表面闪络击穿3维全电磁等离子体流体模拟北大核心CSCD

通过建立电磁场等离子体流体耦合物理模型,基于自主研发的3维全电磁粒子模拟大规模并行程序NEPTUNE3D,编制了3维电磁场与等离子流体耦合程序模块,对1.3GHz高功率微波窗内表面闪络击穿物理过程进行了数值模拟。研究结果表明:微波窗内侧表面形成的等离子体构型与初始种子电子分布形式密切相关。中心点源分布下,等离子体发展为"蘑菇"形状,输出微波脉冲缩短并不严重,等离子体吸收微波功率大于反射微波功率;面源分布下,等离子体发展为"帽子"形状,输出微波脉冲缩短严重,输出微波完全截断,开始阶段等离子体吸收微波功率占优,待等离子体密度增加到一定程度后,反射微波功率占优。通过降低窗体表面场强、表面释气率及初始种子电子密度等方法,可不同程度地延长输出微波脉冲宽度。窗体表面不同气体层厚度对闪络击穿下的输出微波脉冲宽度影响不大。     

kW级功率驱动的锁相高功率微波发生器

针对kW级微波驱动的锁相GW高功率微波,设计了一个高增益(大于50 dB)四腔相对论速调管放大器(RKA)。模拟表明,在此条件下高次模振荡严重影响器件的锁相实现。由此,将RKA结构与正反馈振荡电路结合起来,建立相应的等效电路来研究这种高次模激励的物理过程(即高次模的激励与中间腔之间耦合强度的相关性)。在高次模振荡的等效电路(即正反馈振荡电路)中,用衰减电阻代替结构中的微波吸收层来研究高次模振荡的抑制机理,衰减电阻通过对反馈过程的控制,提高了电路的自激振荡起振电流。在结构上按照衰减电阻要求设计了微波吸收层,将高次模振荡的起振电流提高到大于器件的工作电流,实现了高增益(约60 dB)条件下高次模激励的抑制。模拟获得了4 kW微波功率驱动的2.3 GW锁相高功率微波,增益接近60 dB。在LTD加速器平台的实验结果表明:注入微波由固态RF种子源提供(功率10 kW),输出功率达到1.8 GW,增益为52.6 dB,90 ns内输入和输出微波的相对相位差小于±10°,实验上实现了kW级注入微波对GW高功率微波的相位锁定。     

X波段新型低阻抗高功率微波源的模拟研究

提出了一种新型低阻抗高功率微波源,能在单个器件内产生两束锁相的相干高功率微波,对两束相干微波进行功率合成有望在单个高功率微波器件中实现更高的功率输出.粒子模拟结果显示,在电压687 k V、磁场0.8 T时,该微波源整体阻抗36?,两束微波的频率都为9.72 GHz,输出功率分别为1.20 GW和2.58 GW,功率效率分别为28%和30%;两束输出微波之间频率抖动小于±3 MHz,相位差抖动小于±3?.     

894nm高温垂直腔面发射激光器及其芯片级铯原子钟系统的应用

报道了自行研制的894 nm高温垂直腔面发射激光器(VCSEL)以及基于此类器件的芯片级铯原子钟系统的应用实验结果.根据芯片级铯原子钟对VCSEL在特定高温环境下产生894.6 nm线偏振激光的要求,对器件的量子阱增益及腔模位置等材料结构参数进行了优化,确定增益-腔模失谐量为-15 nm,使器件的基本性能在高温环境下保持稳定.研制的VCSEL器件指标为:20—90?C温度范围内阈值电流保持在0.20—0.23 m A,0.5 m A工作电流下输出功率0.1 mW;85.6?C温度环境下激光波长894.6 nm,偏振选择比59.8:1;采用所研制的VCSEL与铯原子作用,获得了芯片级铯原子钟实施激光频率稳频的吸收谱线和实施微波频率稳频的相干布居囚禁谱线.     

Relativistic X-band BWO with 3-GW output power

Results from a study of a relativistic X-band backward-wave oscillator (RBWO) with 3-GW output microwave power are presented. The RBWO was driven by the high-current electron accelerator SINUS-7. The dependence of radiated microwave pulse duration on microwave power was obtained. Pulse shortening occurring at the higher power levels is probably attributable to explosive electron emission from the slow wave structure (SWS). An increase in the cross section of the electrodynamic structure seems to be a way to increase the microwave pulse duration. Experimental results from a moderately oversized X-band RBWO using a resonance reflector are described. This tube can be operated with a low external magnetic field     

过模返波管的正反馈机制

作为一个典型的高功率微波振荡器,过模返波管(backward wave oscillator,BWO)的束波互作用过程复杂,束流负载效应影响明显,但是作为振荡器本身,其本质就是一个正反馈电路,电子从阴极发射后,穿过谐振反射腔和慢波结构(slow-wave structure,SWS),在SWS区电子动能转化为微波能,其中的一部分微波反馈到谐振反射腔,实现对电子束的调制,其他微波通过后面输出端口向外辐射.本文根据这种正反馈机制,建立器件工作模式等效电路和束波互作用的自洽过程,从理论上给出正反馈机制对器件模式控制、起振电流等参数的影响,并模拟研究了这种反馈机制对模式控制的影响,由此设计了一个能够在(1 MV,20 kA)电子束条件下克服模式竞争的过模BWO,其微波输出功率为7.9 GW,频率为8.68 GHz,相应的效率为39.5%.     

用八孔耦合器识别TM0_(1)/TE_(11)混模中TE_(11)模式的方法北大核心CSCD

在高功率微波传输系统中,为了提高功率容量和效率,往往采用过模波导,因此圆波导中往往出现TM_(01)和TE_(11)混合模式的情况。采用角向均匀分布的8孔圆波导耦合器,对提取TE_(11)模式的混合比和极化角度的方法进行了分析和研究。分析了圆波导中TM_(01)和TE_(11)模式在耦合孔处的电场分布,并采用CST对各耦合孔的输出功率进行了模拟计算,得出相互正对的耦合孔的平均功率与8个孔的平均功率之比与模式之间的相位差无关的结论。同时,发现该比值与TE_(11)模式的混合比成线性关系,线性关系中的比例系数是极化角度线性函数。通过线性拟合获得了计算TE_(11)模式混合比和极化方向的表达式。与仿真设定的参数相比,用该表达式计算的结果表明,在TE_(11)模式混合比小于30%时,用其计算TE_(11)模式的混合比和极化角度是可行的,误差不超过10%。在此基础上,给出了实际情况下TE_(11)模式信息的具体判断方法。     

发光等离子体对6GHz高功率微波的防护性能研究

为研究发光等离子体对高功率微波的防护性能,建立了一维条件下等离子体与高功率微波相互作用的物理模型,并采用数值仿真得到了不同条件下的微波透射效果,分析了发光等离子体对高功率微波的防护性能。随后,实验研究了双层柱状等离子体阵列对6 GHz高功率微波脉冲的透射效果,实验结果与仿真结果相符,说明高功率微波的入射使等离子体产生了非线性效应。实验结果还表明,TE极化时的防护效果要优于TM极化时的防护效果;等离子体击穿场强阈值随电场作用空间的增大而减小;TE极化时等离子体对高功率微波脉冲的屏蔽效能最高可达13 d B,且随入射功率的增大而进一步增大。