Development and test of an L-band magnetron

An L-band relativistic magnetron has been designed, built, and tested at approximately 1.1 GHz. The authors have obtained a peak RMS power of 2.4 GW in one waveguide, and a total of 3.6 GW from two waveguides. The overall efficiency reached 9%, compared with the input power. In contrast with previous S- and X-band magnetron results, the L-band magnetron impedance does not collapse at the end of the pulse, and microwave generation tends to last as long as high voltage is applied. This implies that large total energies can be produced by applying long high-voltage pulses     

Experimental results from a tandem BWO-TWT system used to generatehigh-power microwaves

A relativistic backward wave oscillator (BWO) in tandem with a traveling wave tube (TWT) amplifier has been used to generate relatively long pulses of high-power X-band microwaves. In these experiments, a BWO is used to modulate the annular relativistic electron beam, which subsequently drives a TWT producing high-power microwave radiation. A special RF sever located between the two structures cuts off microwaves generated in the BWO from the TWT. Peak powers in excess of 100 MW are observed with overall beam-to-microwave efficiencies as high as 35%. By operating the BWO below saturation levels, pulse-shortening effects are minimized so that microwave pulses of duration comparable to that of the beam (100 ns) are possible. The operating frequency of the tandem system is tuned from 11 to 12 GHz by varying the effective energy of the beam     

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-band dielectric Cerenkov maser amplifier experiment

An X-band dielectric Cerenkov maser amplifier experiment is reported. The amplifier system consisted of a solid, thermionically generated electron beam propagating through a cylindrical waveguide partially filled with an annular, dielectric liner. The input signal was provided by a tunable (9-10.3 GHz) magnetron with power up to 10 kW. Electron beam voltages and currents of up to 250 kV and 100 A could be generated for 1 μs pulse durations. The system was configured to operate in the TM₀₁ mode of the dielectric-lined waveguide. In this experiment the gain of the system with respect to the length of the dielectric liner was studied at a fixed input frequency of 10.3 GHz. At electron beam parameters of 160 kV and 60 A, a power gain of 24 dB over 56 cm of interaction length was measured for an input power of 4.5 kW, corresponding to a maximum RF amplified power of 1.15 MW and 12% efficiency     

The type and extent of non-LTE in argon arcs at 0.1-10 bar

A 30-A, 3-mm-diameter, wall-stabilized argon arc with 1% hydrogen is examined spectrometrically at pressures of 0.1-10 bar. Values of T_g, and T_exa diverge as pressure decreases below 5 bar (n_e⩽1×10¹⁷ cm^-3) at r=0. T_exβ is 20-40% larger than the other temperatures. The results are dependent on the transition probability scale used     

Pressure limits for the vacuum arc deposition technique

Observations of the cathodic copper plasma expansion at low pressures of He, Ar, and SF₆ showed that, for background gas mass densities of ρ_g=1 to 4×10^-4 kg/m ³ and higher, the plasma and gas are separated into two volumes. A shock wave acts as a boundary between the two volumes. The boundary attains a stationary position once its expansion velocity decreases to the velocity of sound in the background gas. This position corresponds to a distance R_c to the cathode that agrees with a snowplow expansion model, giving R_c ^βf=E_r, where f is a function of the arc current and background gas characteristics, E _r is the erosion rate of the cathode, and β varies between 2.1 and 2.5. The interaction model is based on kinetic energy exchanges between two gas-like volumes without other energy losses. A maximum pressure limit for vacuum arc deposition is set for ρ_g /I=2 to 9×10^-6 kg/m³ A     

X-ray laser research at the LULI (Palaiseau)

The X-ray laser program at Palaiseau is based on the recombination scheme in lithiumlike ions, which requires a moderate pump power and seems to be promising for the purpose of scaling to shorter wavelengths. In aluminum plasmas, peak gain values of 2-2.5 cm^-1 have been obtained at a wavelength of 105.7 Å corresponding to the 3d -5f transition, 6 ns after the top of a 2 ns laser pulse. The same transition in sulfur is emitted at 65.2 Å and has shown a gain of 1 cm^-1 in a preliminary time-integrated experiment. Simulations using a collisional-radiative model as the postprocessor of a hydrodynamic numerical code predict amplifications for the 3d-4f, 3d-5f, and 4d-5f transitions. A new experiment, in progress at the present time, has been designed to enhance the gain-length product up to 10-15 at 105.7 Å. The recently extended facilities of the LULI make it possible to produce a 6-cm-long plasma column, keeping the flux density at the same level as in the previous experiments     

Performance characteristics of a high-power X-bandtwo-cavity gyroklystron

The operating characteristics of a two-cavity X-band gyroklystron experiment are reported. Beam voltages and currents up to 440 kV and 200 A, respectively, are generated in 1 μs pulses by a thermionic magnetron injection gun. Velocity ratios (ν_⊥ /ν_z) near one in the output cavity are used to achieve peak powers of 24 MW near 9.87 GHz. The maximum saturated efficiency of more than 33% occurs at a beam voltage of 425 kV and a current of 150 A. A large signal gain in excess of 34 dB is realized by operating the input cavity just below the start oscillation threshold. Details of tube stability and the dependence of amplification on magnetic field profile, input signal parameters, and various beam quantities are presented     

A two-component model for the electron distribution function in ahigh-current pseudospark or back-lighted thyratron

Temperature, energy, and densities of two electron distribution function components, including an isotropic bulk part and an anisotropic beam, are analyzed for a hydrogen pseudospark and/or back-lighted thyratron switch plasma with a peak electron density of 1-3×10¹⁵ cm^-3 and peak current density of ≈10⁴ A/cm². Estimates of a very small cathode-fall width during the conduction phase and high electric field strengths lead to the injection of an electron beam with energies ⩾100 eV and density of 10¹³-10¹⁴ cm^-3 into a Maxwellian bulk plasma. Collisional and radiative processes of monoenergetic beam electrons, bulk plasma electrons and ions, and atomic hydrogen are modeled by a set of rate equations, and line intensity ratios are compared with measurements. Under these high-current conditions, for an initial density n_H2=10¹⁶ cm^-3 and electron temperature of 0.8-1 eV, the estimated beam density is ≈10¹³ -10¹⁴ cm^-3. These results suggest the possibility of producing in a simple way a very high-density electron beam     

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     

L波段三维ESR成像系统的研制(Ⅳ)--系统组成与各部分性能指标

报道了自行研制的L波段三维电子自旋共振成像（3D-ESRI）系统的整机结构及各部分性能指标. 该系统主要由L波段ESR谱仪、三维梯度磁场装置、数据处理及图像重建软件组成. 系统的微波频率为1.05 GHz;最大微波功率500 mW. 采用3-环2-缝再进入式谐振腔,无载Q值>1 000;最大测量体积为φ 20 mm, 高30 mm柱状水溶液样品. 接收系统采用100 kHz锁相放大电路,最大增益可达1×10⁶;时间常数0.02 ms～1 s;磁场调制幅度>0.5 mT. 最大梯度磁场2 mT/cm;三维梯度线性度均优于5 ％;稳定度可达10^-5;主磁场可在1.6～96 mT范围内任意点选择扫场起始点;在0.2～16 mT范围选择磁场扫描宽度. 数据系统为12位A/D实现数据采集,三路8位D/A控制梯度磁场. 采用滤波反投影法实现图像重建, 成像功能包括：二维、三维自旋浓度成像;等浓度线2D图像显示;3D立体和断层图像显示等. 对水溶液和固体模型样品进行ESR成像的结果表明：本系统可以开展较大体积生物样品的ESRI研究.     

Monte Carlo simulation of electron swarms in nitrogen in uniformE×B fields

The motion of electrons in nitrogen in uniform E× B fields is simulated using the Monte Carlo technique for 240⩽E/N⩽600 Td (1 Td=1×10^-17 V cm²) and 0⩽B/N⩽0.45×10^-17 T cm³ . The electron-molecule collision cross sections adopted are the same cross sections as those used previously for the numerical solution of the Boltzmann equation. The swarm parameters obtained from the Monte Carlo simulation are compared with the Boltzmann solution and with the experimental data available in the literature. In relation to E×B fields, it is concluded that the Monte Carlo approach provides an independent method of substantiating the validity of the equivalent electric-field approach     

Validity conditions for complete and partial local thermodynamicequilibrium of nonhydrogenic level systems and their application tocopper vapor arcs in vacuum

Validity conditions for complete and partial local thermodynamic equilibrium (CLTE and PLTE) of homogeneous, time-dependent, and optically thin plasmas are derived. For Cu I, electron densities of n_e⩾(5×10²²-5×10²³ ) m^-3 are required for the establishment of CLTE. For Cu I and Cu II, n_e⩾(5×10²¹-5×10²¹ -5×10²²) m^-3 is necessary for PLTE (for electron temperatures of 1-2 eV). Application to low-current copper vapor arcs in vacuum shows that CLTE can be expected for r<200-600 μm (r=distance from the cathode spot). A further limitation follows for temperatures of 2 eV or higher if diffusion effects are taken into consideration. Consequently, the use of the LTE formulas in plasma spectroscopy of low-current vacuum arcs is very limited     

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%.     

Design of a high-efficiency C-band backward wave oscillator

For practicability of the high power microwave source,a C-band backward wave oscillator(BWO)which has high conversion efficiency is designed.When the axial guiding magnetic field is 0.83 T,the electron energy and the beam current of the diode are respectively 80 keV and 2.1 kA,a microwave output power of100 MW at 7.4 GHz microwave frequency with 65% conversion efficiency is achieved in simulation.     

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在HL-2A装置上研制了用于测量等离子体密度分布的两套幅度调制微波反射仪。微波反射仪采用时间延迟法。这两套微波反射仪有不同的频率范围(26.5～40GHz和40～60GHz),它们所对应的密度测量范围是(0.84～1.98)×1019m-3和(1.98～4.47)×1019m-3。时间分辨率可达1ms,空间分辨率约为5mm。     

A microwave generated plasma in a tunable resonant cavity forstudies of turbulence in weakly ionized gases

A microwave plasma in argon is generated inside a pyrex tube by a 3-kW power supply in combination with a magnetron, wave guide, and a resonant cavity. The gas pressure is varied from 200 to 2000 mtorr, and the microwave output power is varied from 600 to 1200 W. Plasma parameters are determined by using a single Langmuir probe. Bias voltage and current characteristic curves are analyzed for the determination of electron temperature, density, and plasma potential. Electron density is found to be in the range of 1.4-7.6 × 10¹¹ cm^-3 , electron temperature 4.2-6.2 eV, and plasma potential 22.6-35.6 volts. Turbulence in plasma emissions can now be studied in these various regimes using Ar I lines     

准两腔振荡器的理论和实验研究

根据两腔振荡器和返波管的特点提出了准两腔振荡器，其作用机理是两腔振荡器的机理，结构类似返波管.这种结构主要由调制腔组和换能腔组两部分组成，调制腔组实现电子束速度调制，调制后的电子束在通过一个微波场较弱的区间时实现电子束群聚，然后在换能腔组实现电子能量到微波能量的转化，并通过输出结构输出；同时，调制腔组和换能腔组之间存在微波耦合，换能腔组中的一部分微波能量可以耦合到调制腔组，形成一个正反馈回路，在一定条件下实现微波振荡.根据此理论，根据Sinus-700加速器的参数(800 kV，10 kA)设计了一个X波段的高功率微波器件，2.5维Particle in Cell (PIC)程序模拟的效率为28%，微波频率为9.42GHz，微波输出功率为2.25GW，实验上得到的微波输出为微波频率9.40GHz，微波输出功率2.44GW. 关键词： 两腔振荡器 返波管 多波切仑可夫微波器件     

Soft X-ray recombination laser research at the Institute of LaserEngineering

Soft X-ray laser experiments recently carried out using the Gekko MII glass laser facility at the Institute of Laser Engineering, Osaka University, are described. Hydrogenic and lithiumlike lasing schemes in recombining plasmas were investigated using foil targets exploded with line-focused 532 nm laser radiation of approximately 100 J energy. In a preliminary study, time-integrated emissions of Balmer-α transitions in C⁸⁺ and O⁷⁺ and 5-3 transitions in Al¹⁰⁺ were found to increase nonlinearly with increasing target length, yielding gain coefficients of G=0.9 to 2.3 cm ^-1. In a subsequent, more refined study, which included time-resolved measurements, the authors obtained a gain of G=2 cm^-1 and a gain-length product GL=3 for the Balmer-α transition in F⁸⁺ at 80.9 Å     

电离层中性气体释放的早期试验效应研究

在电离层释放电子吸附类中性气体能够引起电离层电子密度耗空,在释放之后快速形成"电离层洞";同时,由于释放气体的快速膨胀,挤压背景等离子体,在电离层洞的外边缘产生"壳状"电子密度增强结构,电离层洞和电子密度增强结构同时存在是释放早期试验效应的显著特征.本文研究了电离层中性气体释放的早期试验效应,建立了释放早期电子密度的时空演化物理模型,仿真了释放早期电子密度的时空演化过程,同时采用射线追踪方法研究了释放后10 s和120 s不同频率信号在扰动区的传播效应,并反演得到了电离层垂直探测电离图,反演结果与一次火箭喷焰的实际观测结果吻合较好,初步验证了本模型的正确性.