Experimental investigation of emission inhomogeneity of gyrotron cathodes basing on their current-voltage characteristics

A scheme for automatic measurement of current-voltage characteristic of gyroresonance devices has been developed. Efficient emission inhomogeneity of cathode in powerful gyrotrons has been studied basing on analysis of current-voltage characteristics. Experimental data on the parameter of efficient emission inhomogeneity for different regimes are presented, as well as the estimate for admissible efficient inhomogeneity of the cathode for powerful gyrotrons and the dependence of electron beam parameters on efficient inhomogeneity of the cathode. A method of complex measurements is proposed, which makes it possible to judge about the contribution of different physical mechanisms into emission inhomogeneity of the cathode.     

W波段三次谐波回旋管实验研究

国内首次成功进行W波段三次谐波回旋管实验。回旋管工作模式为TE61,磁场1.2 T,采用拍频法测定工作频率为94.86 GHz。电子束电压为45 kV时,电流1.6 ~ 4.4 A范围内都观测到了三次谐波振荡信号。采用焦热计测定最大输出功率4.9 kW,效率约 3%。     

液滴撞击固体表面铺展特性的实验研究

利用高速摄影仪记录了不同液滴撞击固体表面的形态变化过程, 并探讨了液滴撞击参数对撞击过程液滴形态的影响. 结果表明: 液滴黏度对液滴铺展过程起着决定性作用, 液滴表面张力对液滴铺展后的回缩起到主导作用, 两者的共同作用决定着液滴的震荡特性; 撞击速度的提高会增大液滴的最大铺展因子, 但达到最大铺展的时间因表面张力的不同呈现不同变化规律.     

The volt-ampere characteristics of the leakage and emission current of sandwich cathodes

The study of the properties of a metal-dielectric-metal system in a strong electric field has so far led to heterogeneous results. Their agreement with theory is unsatisfactory or lacking entirely. The theoretical conceptions are based on the assumption of the field emission of electrons from the surface of metals to the conduction band of the dielectric and from there by passage through the second metal electrode to vacuum. A perfect dielectric is assumed here. This assumption is probably not fulfilled when realizing the cathodes, as can be estimated from a comparison of the technology of producing a dielectric, for example, with the preparation of intrinsic semi-conductors. The presence of defects in the dielectric layer may have a decisive influence on the properties of the cathodes. In this way we can obtain different results even when using the same materials for making the cathodes.The present paper deals with the influence of the thickness of the dielectric on the electrical properties of cathodes. Two different dielectrics were used, produced in different ways: a dielectric dependent on the metal electrode (oxidizing cathodes) and independent (evaporated cathodes).In conclusion, the author thanks L. Sodomka and K. Frainic for assistance in the experiments.     

Experimental study of a gyrotron operated at the second gyrofrequency harmonic with the single-stage energy recovery

We obtain an output efficiency of 60%, which is record-breaking for gyrotrons operated at the second gyrofrequency harmonic, for an output power of 6 kW in the continuous-wave regime. The increase in the efficiency is achieved by using single-stage energy recovery in a gyrotron with an electrically insulated collector. Experimental results confirm the validity of calculation of the electron-beam energy spectra in the gyrotron collector region. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 10, pp. 850–854, October 2008.     

Analysis of current-voltage characteristics of inhomogeneous Schottky diodes at low temperatures

Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current-voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current-voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current-voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.     

Measurements of the spread in the initial electron energy in a gyrotron

An analyzer intended for measuring electron energy in gyrotrons is described. Electron energy spectra are measured in various operating modes of an experimental gyrotron. It is shown that, even when no microwave field is generated, the spread in electron energy due to the space-charge effect can be as high as several percent.     

碳纳米管冷阴极脉冲发射特性及仿真模型研究

针对碳纳米管场致发射冷阴极在微波、毫米波电真空辐射源器件中的应用需求,采用2μs,20 kV的脉冲高压对碳纳米管场致发射冷阴极的脉冲发射特性进行了实验研究.通过改变阴阳极间距,对碳纳米管冷阴极发射电流特性及发生脉冲高压打火后的碳纳米管冷阴极发射特性进行了测试研究.在直径为4 mm的圆形平面碳纳米管冷阴极上获得最大发射电流16 mA,电流密度为127 mA/cm~2.以实验测试数据为基础,结合粒子模拟软件建立碳纳米管冷阴极场致发射仿真模型,给出了该仿真模型的相关参数,为下一步设计研制碳纳米管冷阴极电子光学系统及相关辐射源器件奠定基础.     

爆炸发射阴极特性的研究进展

文章对爆炸发射阴极的物理机制进行了阐述,着重对爆炸发射阴极的各种特性进行了介绍,包括阈值电压、发射均匀性、等离子体闭合速率、阴极寿命等.并且对研究爆炸发射阴极特性所采用的理论和测量方法进行了介绍,给出了目前阴极材料使用中存在的问题.     

爆炸发射阴极特性的研究进展

文章对爆炸发射阴极的物理机制进行了阐述，着重对爆炸发射阴极的各种特性进行了介绍，包括阈值电压、发射均匀性、等离子体闭合速率、阴极寿命等．并且对研究爆炸发射阴极特性所采用的理论和测量方法进行了介绍，给出了目前阴极材料使用中存在的问题．     

基于沉淀工艺制作四脚氧化锌纳米材料场致发射阴极的研究

采用沉淀法制备四脚氧化锌纳米材料场致发射阴极，将阴极和荧光屏封装起来抽真空并对屏施加电压，测试阴极的发射电流和荧光屏的发光亮度.利用沉淀法制备出面积为(13×15) cm²的阴极，测试结果表明，硅酸钾体积百分比在50×10^-3—83×10^-3范围，硝酸钡浓度在50×10^-4—77×10^-4 M范围，四脚氧化锌的浓度在82×10^-4—12×10^{-3相似文献}   

基于沉淀工艺制作四脚氧化锌纳米材料场致发射阴极的研究

采用沉淀法制备四脚氧化锌纳米材料场致发射阴极,将阴极和荧光屏封装起来抽真空并对屏施加电压,测试阴极的发射电流和荧光屏的发光亮度.利用沉淀法制备出面积为(13×15) cm²的阴极,测试结果表明,硅酸钾体积百分比在50×10^-3—83×10^-3范围,硝酸钡浓度在50×10^-4—77×10^-4 M范围,四脚氧化锌的浓度在82×10^-4—12×10^{-3关键词： 场致发射 沉淀法 显示屏亮度}     

TE_(02)模式95 GHz三次谐波回旋管实验

首次实现W波段三次谐波回旋管输出功率突破10kW。谐波回旋管互作用结构采用带有光阑结构的圆柱型开放式谐振腔,工作模式为低损耗圆对称模式TE02。实验中,在脉冲宽度20μs、电子束电压45kV、电流3A、磁场1.23T时,测得工作频率为95.22GHz,输出功率13.4kW,对应效率9.9%。     

早龄期荷载及低温作用下的混凝土声发射特征试验研究*

井壁混凝土由于施工与环境特殊性导致其裂缝扩展情况异常,本文通过对不同早龄期荷载、低温条件下混凝土轴压破坏过程的声发射检测,分析井壁施工环境对混凝土内部裂缝产生、发展的影响。研究表明,早龄期荷载、低温单独作用时,与标养混凝土主要差异在轴压过程中的声发射初始阶段,对混凝土内部的原有收缩裂缝有所影响。当两者耦合作用时,早龄期荷载影响比低温作用显著,并且在早龄期荷载较大时会出现声发射信号"倒置"现象。     

Field emission and current-voltage properties of boron nitride nanotubes

We have measured electrical transport properties of boron nitride nanotubes using an in situ manipulation stage inside a transmission electron microscope. Stable currents were measured in a field emission geometry, but in contact the nanotubes are insulating at low bias. At high bias, the nanotubes show stable, reversible breakdown current.     

Leakage and emission characteristics of condenser cathodes with thin layer of Al2O3

The paper gives the leakage and emission characteristics of sandwich cathodes of the type Al-Al₂O₃-Au prepared on polycrystalline Al and on a layer of Al deposited in vacuum with a layer of Al₂O₃ 100–500 Å thick. The samples with a monotonous leakage characteristic have an exponential emission characteristic and the samples with anomalous leakage characteristic showing a maximum have an emission characteristic beginning at anomally small voltages on the sample and in the energy spectrum they exhibit excess energy. The relationship between these two types and the method of preparing the layers is given. Measurements are described which bear witness to the slow processes taking place in the cathode and the paper gives hypotheses on the mechanism of emission from such cathodes.Thanks are due to I. Emmer who prepared a number of samples and performed several measurements (Figs. 3, 10) for paper [14] which the present author has used here.