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     

Gain properties of a wide aperture X-ray pre-ionized excimer amplifier

A wide aperture, X-ray pre-ionized discharge pumped excimer laser was comparatively studied as oscillator and amplifier with XeCl and KrF as the active gases. With XeCl (KrF), an oscillator output energy of 3J (1 J) and a small-signal gain coefficient of 11%cm^–1 (6%cm^–1) were measured. The beam size was 6×5 cm². For smaller beam widths (obtained by limiting the pre-ionized region), both excimers showed considerably higher gain. The dependence of output parameters on the X-ray dose was studied for both excimers.     

同轴虚阴极谐振效应研究

中国工程物理研究院应用电子学研究所的一些实验表明由阳极反射板、阳极网和阴极发射的电子束形成的环状虚阴极围成的准谐振腔是决定同轴虚阴极输出微波功率和传输模式的关键所在. 在二极管电压350kV，电流23kA条件下，获得了500MW的微波输出功率，能量转换效率约6.2％，工作频率3.3GHz，输出微波主要由TM₀₁模式和TE₁₁模式组成. 对同轴虚阴极的谐振效应进行了分析. 关键词： 高功率微波 同轴虚阴极 谐振腔 模式竞争     

Plasma density measurement in a gas-filled X-band backward wave oscillator with a double conversion heterodyne microwave interferometer

Plasma density was measured with a heterodyne microwave interferometer in both a gas-filled X-band backward wave oscillator (BWO) and in a smooth tube. Plasma is generated by impact ionization of a 650 kV, 2 kA electron beam. For fixed gas pressure we found that the plasma density rise in the operating BWO was much faster than in a smooth tube, indicating that Trivelpiece-Gould modes, or high power microwaves, increase plasma generation. Additional plasma enhanced BWO microwave output power. Measured plasma density at optimum power levels was n_cr ≈ 6 × 10¹²cm⁻³ at onset of emitted microwaves.     

Parameters of the beam plasma formed by a forevacuum plasma source of a ribbon beam in zero-field transportation system

We have studied the generation of the beam plasma formed by a forevacuum plasma source of a ribbon electron beam in the conditions of its transportation without an accompanying magnetic field. The ignition conditions in the beam transportation region of the beam–plasma discharge producing a plasma formation of the plasma sheet type with a plasma concentration of ~10¹⁶ m^–3 and an electron temperature of 1–2.5 eV have been determined. The attained values of parameters and the sizes of the plasma formation make it possible to use it in technologies of the surface modification of planar extended articles.     

Passively mode-locked Yb:KLu(WO4)2 thin-disk oscillator operated in the positive and negative dispersion regime

We demonstrate a passively mode-locked femtosecond Yb:KLu(WO(4))(2) thin-disk laser oscillator. Chirped-pulse operation in the positive dispersion regime as well as solitary operation have been realized, and the laser performance of both configurations are compared. In the solitary mode-locking regime the output power exceeds 25 W in a diffraction-limited beam, and pulse durations as short as 440 fs at a 34.7 MHz repetition rate have been generated. For the first time we present a chirped-pulse operation of a thin-disk oscillator that yields a maximum average output power of 9.5 W with a Fourier limit of 450 fs.     

侧面泵浦主振荡功率放大器中的光束质量提高

报道了一种利用球差补偿效应提高侧面泵浦主振荡功率放大器输出光束质量的实验装置。在理论上提出了一种新的球差补偿方法,利用正球差经过会聚透镜焦点后向负球差转化的现象,补偿下一放大级中的正球差效应。在实验上搭建了两级放大的侧面泵浦Nd:YAG主振荡功率放大器。在连续输出的情况下,从振荡级输出功率为42W、光束质量因子为1.48的种子光,经过一级放大后的功率为74W,光束质量因子恶化为1.80;继续经过二级放大后,光束质量因子提高为1.40。实验结果表明,所提出的球差补偿理论是提高激光放大过程中光束质量的有效手段。     

Cascade processes in a plasma oscillator

A theoretical and numerical analysis is made of the dynamics of nonlinear electron-beam scattering of a wave reflected by the emitting device of a plasma oscillator. It is shown that a counterpropagating plasma wave can interact nonlinearly with other waveguide modes of the system and with charge-density beam waves, leading to changes in the operation of the oscillator. It is established by means of a numerical simulation that the generation efficiency is reduced as a result of scattering of the counterpropagating wave and stimulated emission of a strong-potential plasma wave with phase velocity v _ph=ω/k _z≪c. Zh. éksp. Teor. Fiz. 112, 1299–1311 (October 1997)     

Relativistic backward wave oscillator using a selective mode converter

A new version of the relativistic backward wave oscillator (BWO) is proposed and investigated experimentally, where the cutoff (for the working mode mode) taper at the cathode end is replaced by a selective Bragg-type mode converter. In the experimental BWO model, which operates in the three-centimeter range and is equipped with a mode converter based on a slightly corrugated waveguide, a radiated power of 700 MW in pulses of duration up to 100 ns with an output spatial structure similar to a Gaussian wave beam is obtained at an accelerating potential of 0.8 MV and a focusing magnetic field of 7 kOe. Zh. Tekh. Fiz. 69, 102–105 (November 1999)     

Nonlinear theory of beam excitation of azimuthal surface modes in plasma-filled cylindrical metal waveguides

It is shown that electromagnetic surface waves propagating along the azimuthal angle can be excited efficiently by an annular electron beam in a cylindrical metal waveguide partially filled with a magnetoactive plasma. A self-consistent system of differential equations is obtained to describe the nonlinear interaction between the beam particles and an azimuthal surface wave in the single-mode regime. This system of equations is analyzed numerically and the influence of the parameters of this waveguide structure on the development of the resonant beam instability is determined. Zh. Tekh. Fiz. 69, 84–88 (July 1999)     

基于开槽单矩形栅和圆形电子注的W波段返波振荡器

提出将开槽单矩形栅和圆形电子注作为 W波段返波振荡器的注波互作用回路. 使用 3维电磁场仿真软件CST-MWS对开槽单矩形栅的高频特性进行了仿真分析, 研究结果表明: 相对于传统单矩形栅, 新结构的基模带宽有所展宽; 基模与高次模发生模式竞争的可能性很小; 在采用圆形电子注时新结构能获得大得多的耦合阻抗; 新结构的趋肤损耗略有改善. 将该慢波结构应用于设计一支以94 GHz为频带中心的W 波段返波振荡器: 设计了简洁的慢波过渡部分、输出耦合器和终端匹配衰减器, 优化参数后获得了良好的信号传输特性; 利用粒子模拟软件CST-PS对返波振荡器模型进行了三维大信号注波互作用计算, 设定合适的电子注电流等参数后, 调整工作电压在较宽的频带内获得了瓦级的功率输出, 电子效率在整个频带范围内优于1%. 关键词： 开槽单矩形栅 圆形电子注 返波振荡器 W波段     

Investigation of the spatial beam quality of pulsed ns-OPOs

This paper reports on an experimental investigation of the spatial beam quality of a pulsed nanosecond optical parametric oscillator (OPO). The OPO is a 355 nm pumped type-I BBO-OPO. The spatial quality of the OPO output is characterized by the M²-parameter in dependence of other experimental parameters such as resonator length, pump-beam diameter, pump-pulse duration and pump energy. The results obtained indicate, that an appropriate choice of these parameters substantially improves the spatial beam quality of the OPO output. Received: 19 November 2002 / Revised version: 3 February 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +49-631/205-3906, E-mail: anstett@rhrk.uni-kl.de     

650 GHz正弦波导返波管的模拟计算

提出了一种利用正弦波导慢波结构设计的太赫兹频段大功率返波管的新方案。3维粒子模拟研究结果显示:在20 kV的工作电压和5 mA的驱动电流下,该返波管在645.9 GHz频率处将具有1.55 W的峰值功率输出,互作用效率为1.55%,频谱纯净,输出模式为TE10模。通过在15～25 kV之间进行电压调谐,可获得80 GHz的调谐带宽,且峰值输出功率都在1 W以上。     

Scaling studies and time-resolved microwave measurements on arelativistic backward-wave oscillator

A relativistic backward-wave oscillator (BWO) operating at a frequency near 8 GHz has been built. The parameters of the 60-ns electron beam driving this microwave source are varied over the ranges 0.8-1.5 MV and 2-10 kA. Several different annular cathodes for launching the electron beam are tried, varying the outer radius and shape. The axial magnetic field guiding the beam through the BWO is varied between 0.6 and 3 T. The power transfer downstream to an output waveguide is investigated as a function of the shape of the transition from the BWO to the waveguide. The scaling of the output power and frequency with these variations is discussed. Time-resolved measurements of 2-ns-long segments of the microwave output are shown. In observations of the microwave signal, it is found that the frequency shifts as the output power envelope passes through a sharp dip. It is proposed that this shift corresponds to a change in the longitudinal operating mode of the BWO     

Excimer lasers and laser systems

The results of the experimental study of UV lasers and laser systems pumped by different methods are presented. Two lasers were pumped by electron beams from Marx generators. Three lasers were pumped by transverse discharge with UV preionization. An XeCl laser pumped by electric discharge using a generator with inductive energy storage and semiconducting opening switch is investigated. The highest laser radiation energies of 2000, 90, and 0.7 J have been obtained at 5=308, 249, and 222 nm, respectively. The amplification of the laser beam from the master oscillator under conditions of strong amplified spontaneous emission is considered. In particular, formation of the output from an amplifier in the wings of the XeCl laser band and in the case of a large-aperture XeCl amplifier are investigated. The output beam divergence in these experiments was measured to be ~10^-4 rad.     

Optical studies of ZnSe/ZnMgSSe-based quantum-well semiconductor heterostructures

Results of an optical study of heterostructures based on new compounds, ZnSe/ZnMgSSe, are presented. The possibility of using these compounds to produce high-quality quantum-well structures having strong exciton features in optical spectra is demonstrated. An analysis of reflectance spectra has yielded the exciton parameters: the resonant frequency, oscillator strength, and exciton line damping. The exciton binding energies have been determined from magneto-optical spectra. The samples studied have a high structural perfection and small inhomogeneous width of the excitonic resonances. Fiz. Tverd. Tela (St. Petersburg) 40, 811–812 (May 1998)     

非磁化等离子体填充的相对论返波管的粒子模拟

 对非磁化等离子体填充的相对论返波管进行了粒子模拟分析，结果表明在一定的等离子密度范围内，观察到电子注的良好传输，得到了高功率电磁波输出。等离子体密度变化过程中，输出存在有峰值功率点。通过粒子模拟清晰地观察到注、等离子体及波相互作用的物理过程，并且模拟结果解释了部分实验现象。     

Double XeCl laser with lateral UV preionization

We present a very compact and very reliable laser system formed of two discharge sections both with lateral UV preionization. The discharge electrodes are contained in a single vessel and form an oscillator-amplifier system. A single spark gap switches on both circuits. By applying a generalized self-filtering unstable resonator to the oscillator and injecting the laser beam into the single pass amplifier, an output beam of 105 mJ, with a brightness of 5.5×10¹³ W cm^–2Sr^–1 has been obtained. Moreover, by applying a pulse-forming network in one discharging circuit, the duration of the discharge breakdown has been increased and output laser pulses of 40 ns FWHM, and 80 ns base width duration (at 10% points) and of energy 100 mJ are obtained.     

电子束注入简单磁镜中被电子迴旋共振加热捕获的实验研究

在简单磁镜MM-2中,在采用15GHz大功率迴旋管进行电子迴旋共振加热(ECRH)的同时,以不同的方式向磁镜中注入电子束,进行了ECRH捕获电子束的实验研究。结果表明:由于电子束的提前注入,等离子体的预电离时间被大大地缩短。由上ECRH对电子束的捕获,使得热电子环参数得到很大的改善,热电子环的反磁β值约增加62%,对应反磁增加的捕获效率约为(30—40)%。在迴旋管输出约30kW的条件下,适应建立热电环的气体压力窗为(4.67—21.3)×10^-4Pa。 关键词：     

Injection-locked single-frequency laser with an output power of?220?W

A solid-state laser system for the next generation of gravitational wave detectors with an output power of 220?W at the wavelength of 1064?nm is presented. Single-frequency operation of the laser was achieved by injection-locking of a high-power ring oscillator to an amplified non-planar ring oscillator (NPRO) following the Pound?CDrever?CHall scheme. The high-power stage which features four longitudinally pumped Nd:YAG laser crystals as active media in a ring resonator configuration was designed for reliable long term operation. Using a non-confocal ring cavity to filter the output beam, a pure TEM₀₀ mode with 168 W output power was obtained.