Effects of graphite intercalation with cesium in a thermionic converter

The thermionic energy converter (TEC) with inter-electrode low-temperature plasma and cesium vapor dynamic flow in the inter-electrode gap (IEG) demonstrated an increase in efficiency of up to 20%. This was mainly reached due to the decrease in the effective electron work function to an anomalously low value of the order of 1 eV from a perforated nickel collector covered with nanosized graphite flakes under the converter working conditions. SEM X-ray microanalysis of the collector surface layers was performed, and the model of the effects proposed.     

Thermionic energy converter in magnetic field

The paper deals with the influence of a magnetic field on the function of a thermionic energy converter. It derives a relation for the effect of the magnetic field on the converter current in a diffusion regime and gives measurements for a quasi-vacuum and diffusion regime of the converter.     

Experimental thermionic energy converter without enclosure: A molecular beam supplied converter

Experimental thermionic energy converters of an open type, i.e. with no closely located surrounding walls, as proposed here, have many advantages compared to conventional enclosed converters. Interactions with and problems of the enclosure do not interfere with the fundamental plasma and surface processes, which can be studied efficiently in an open converter, for example by mass spectrometry, optical spectroscopy, electron energy analysis and surface analytical methods. An open converter has been built and tested, where the necessary alkali vapour is supplied by a molecular beam type source with 400 laser bored effusion holes. The source acts as collector in front of a directly heated emitter. An ignited mode behaviour can be reached easily. The examples of results presented for Mo and Pt emitters at 1600–1700 K, a Cs plasma and nickel collector give a power density of 1–2 W cm^–2 and a minimum barrier index of 1.95–2.1 eV and indicate a behaviour similar to enclosed converters. Thus, results for new surfaces, new additives etc. found in open converters should be of direct relevance for the development of normal enclosed converters.     

引导磁场对收集极中电子能量沉积的影响

理论分析了引导磁场对收集极材料中电子运动的约束作用,推导了引导磁场作用下二次电子的逃逸条件,利用蒙特卡罗方法计算了引导磁场作用下电子束在收集极中的能量沉积规律。研究结果表明:引导磁场对电子在材料内部的运动约束作用很弱,对二次电子有强约束作用;大部分二次电子经拉莫回旋再次轰击在收集极上被收集,逃逸的二次电子沿引导磁场方向进入束波作用区;增大电子的入射角度时,束流密度的降低和二次电子的再次入射降低了收集极中电子的最大沉积能量密度,提高了收集极的耐电子轰击能力。     

Atomic coherence effects on optically pumped cesium atoms in static magnetic field

The population difference between ground states F = 4 and F = 3 is calculated for Cs atoms pumped on the D₂ line by a resonant laser beam. The pumping efficiency for Cs atoms in a static magnetic field on two hyperfine transitions (6S_1/2 F = 4 → 6P_3/2 F′ = 3 and F′ = 4) is calculated for various pump laser intensities. The population difference as a function of the static magnetic field exhibits a dip centered at the zero magnetic field, which corresponds well with the Zeeman coherence between sublevels of the F = 4 state. The full-width at half-maximum (FWHM) of the dip as a function of the pump laser intensity shows abnormal power broadening behavior that differs for different hyperfine transitions. We present experimental results that agree with the theoretical calculations.     

能量输运对柱状等离子体开关磁场穿透过程的影响

 对于高密度、导通时间为μs级的柱状等离子体开关,利用磁流体动力学理论(MHD),对其导通阶段的磁场穿透过程进行了模拟,得到了磁场分布随时间的变化;研究了开关导通过程中能量输运导致的温度不均匀分布对磁场穿透过程的影响。模拟结果表明：对于高密度等离子体开关,磁场以远大于磁扩散速率的速度穿透到等离子体中;在磁压对等离子体产生的压缩效应和欧姆加热效应共同作用下,激波区域的等离子体温度显著升高,这进一步加速了磁场穿透;当考虑能量输运方程时,开关导通时间为0.87 μs,比等温模型的结果0.92 μs短,与实验结果0.87 μs相一致。     

能量输运对柱状等离子体开关磁场穿透过程的影响

对于高密度、导通时间为μs级的柱状等离子体开关,利用磁流体动力学理论(MHD),对其导通阶段的磁场穿透过程进行了模拟,得到了磁场分布随时间的变化;研究了开关导通过程中能量输运导致的温度不均匀分布对磁场穿透过程的影响。模拟结果表明：对于高密度等离子体开关,磁场以远大于磁扩散速率的速度穿透到等离子体中;在磁压对等离子体产生的压缩效应和欧姆加热效应共同作用下,激波区域的等离子体温度显著升高,这进一步加速了磁场穿透;当考虑能量输运方程时,开关导通时间为0.87 μs,比等温模型的结果0.92 μs短,与实验结果0.87 μs相一致。     

Simplified calculations of a thermionic converter in the ignited mode

The charged particle transport in the plasma of a thermionic converter in the ignited mode is treated to be due to the charged particle density gradient and the electric field. The corresponding coefficients as well as the numerical treatment of the ionization and recombination processes are taken from the literature, the latter one in a suitable approximation. The electron temperature is assumed to be uniform within the gap. Taking account of the boundary conditions for the electron and ion currents and for the flux of the kinetic electron energy analytical solutions are found whose numerical evaluations can easily be performed. To make allowance for the Schottky effect and a double sheath at the emitter surface is shown to be necessary and possible with moderate effort for the calculation of I-V curves. The validity limit of the model is discussed.     

Influence of magnetic field on exciton luminescence

The magnetic field dependence of the exciton emission intensity I_ex(H) has been investigated in Ge crystals stressed along the direction near 〈100〉. In the low field limit the magnetic field correction has been evaluated to the wave functions of the ground and some excited states of an isotropic exciton. The calculated dependence I_ex(H) in the case of Ge is in a good agreement with the experimental one at H ? 0.5 T.     

Influence of cesium atoms on the field electron emission from multi-walled carbon nanotubes

It has been shown that the deposition of cesium atoms on multi-wall carbon nanotubes abruptly increases the current of the field electron emission, decreases the threshold electric field by a factor of three (to 0.8 V/m), and decreases the work function to 2.1–2.3 eV. It has been found that the flowing of the large emission current I ≥ 2 × 10^?6 A leads to a change in the current-voltage characteristics and a decrease in the emission current. This effect has been explained by escape of cesium atoms from the tips of most nanotubes into the nanotube depth due to desorption or intercalation. At the same time, the low work function is retained for some nanotubes, probably, due to the stronger bonding of Cs atoms with these nanotubes.     

基于新型三电平变流器的超导磁储能系统设计

为改善超导磁储能系统在充放电过程中的输出特性,并提高其能量转换效率,在分析了A-NPC三电平变流器拓扑结构及其工作原理的基础上,以此变流器为核心,设计了一套超导磁储能系统。该系统采用一种基于SVPWM调制的三电平直接功率控制策略,并利用功率前馈解耦算法,实现了储能系统充放电过程中的单位功率因数控制。实验结果表明,储能系统充放电过程稳定可靠,工作效率有效提高,并能获得良好的电流、电压波形。     

扫场对核磁共振测量的影响

在连续波核磁共振实验中,通常采用低频扫场产生重复再现的共振吸收信号。当处于磁场中的射频线圈引线回路等效面积不为零时,简谐扫场必然引起该闭合回路的磁通量变化,由此而产生同频简谐感生电动势并与核磁共振信号叠加共同构成振荡器输出信号。由于扫场上升和下降过程的感生电动势方向相反,从而扫场前半周和后半周所对应的共振吸收测量信号存在差异。实验结果表明：扫场强度及方向对核磁共振测量影响来源于实验测量技术缺陷,而非核磁共振的物理本质。     

磁场对光抽运信号的影响

在做光泵磁共振实验时,分别研究了竖直线圈和水平线圈产生的磁场对光抽运信号的影响,并做出了它们之间的关系曲线.由此曲线计算了北京地磁场的垂直分量为(0.0881±0.0015)×10-4T,估算出北京地磁场的水平分量约为0.425×10-4T.同时,这项工作对于区分光抽运信号和磁共振吸收信号也有一定的帮助.     

超导磁储能变流器的超螺旋滑模控制策略研究

针对超导磁储能(Superconducting Magnetic Energy Storage,SMES)变流器采用传统滑模控制方法时存在较大的抖振问题,研究了一种超螺旋滑模控制策略用于改善这一现状。根据SMES变流器拓扑结构进行建模分析,然后选取d、q轴的电流误差值作为积分滑模面,设计了超螺旋滑模控制器。该控制器包含了等效控制和切换控制两部分,其中采用超螺旋控制率的切换控制仅在趋近阶段起作用,使跟踪误差能够在有限时间内收敛为零;当系统状态到达准滑模态时采用等效控制,有效地削弱了抖振幅度。MATLAB/Simulink仿真结果表明,所提出的控制策略较PI控制以及传统滑模控制有着更小的抖振和更高的动态响应性能。     

Photoneutrino energy loss rates under magnetic field

The neutrino energy loss rate is calculated due to the photoneutrino process in a hot plasma, under magnetic field.

The calculations done for low densities and relatively low temperatures may be used for astrophysical estimations in neutron stars.

     

垂直磁场对光抽运信号的影响

保持扫场和垂直磁场合成的叠加磁场大小一定,定量研究了地磁场的垂直分量抵消不同时叠加磁场方向变化角度Δθ对光抽运信号幅度的影响.结果表明:光抽运信号幅度随叠加磁场方向变化角度Δθ的增大而增大,当Δθ=180°时,即地磁场的垂直分量完全抵消时,光抽运信号幅度最大,并用量子理论的观点解释了这一规律.     

Xenon induced changes of plasma drop and electron temperature of a thermionic converter

The I–V curves of a thermionic converter were measured for several cesium pressures and various electrode distances, and partial pressures of added xenon as well. The minimum internal voltage drop across the electrode gap was determined and correlated with cesium pressure, spacing and xenon pressure. Without xenon added this voltage drop shows the well-known minimum at an optimum pressure-spacing product ofp _Cs d=5·10⁻²cm·Torr. Only for smaller values of the pressure-spacing product the internal voltage drop can be reduced by the addition of xenon. An interpretation is achieved by a comparatively simple model assuming a uniform electron temperature in the electrode gap. Using this model, the electron temperatures were calculated for various spacings and xenon pressures. Comparing the experimental data of the internal voltage drop and the correspondingly calculated electron temperatures it turns out that, within the framework of the model used, the internal voltage drop is represented by the electron temperature. The electron temperature itself is determined by the ion balance. Presented at the 10th Intersociety Energy Conversion Engineering Conference, Newark, Delaware, USA (1975).     

Influence of switchable magnetic field on the modulation property of nanostructured magnetic fluids

Magnetic fluid is a kind of colloidal material with tunable microstructure and unique optical properties. The tunable magneto-optical modulation property of magnetic fluid under externally switchable magnetic field with various modulation periods is investigated theoretically and experimentally. The transitional modulation period (lower limit of the working frequency) between the square-like and oscillation-like modulation is achieved and found to be magnetic-field- and sample-concentration-dependent. The modulation mechanism is analyzed and ascribed to the dynamic microstructure of magnetic fluid under different modulation periods of external magnetic fields. The result of this work may be helpful for the pragmatic applications of magnetic fluid based on the square-like modulation.     

高能等离子体入射对磁场膨胀影响的模拟研究（已撤稿）

采用三维模型，使用混合网格质点法对等离子体入射偶极子磁场产生的磁场膨胀进行数值模拟.在模拟中考虑了高能等离子体注入两种不同类型磁场的情况：等离子体注入没有背景磁场的偶极子磁场和等离子体注入有背景磁场的偶极子磁场.研究表明背景磁场的存在不仅改变了粒子的分布，还改变了磁场膨胀的程度.还研究了注入的高能等离子体的速度对磁场膨胀的影响，结果表明入射的高能等离子体速度越大，磁场膨胀的程度就越大.对于低的入射速度，入射粒子在偶极子磁场中的回旋半径与偶极子磁场的特征长度相比较小，粒子被磁场束缚，对偶极子磁场的影响可以忽 关键词： 网格质点法 磁场膨胀 偶极子磁场