Relativistic Cherenkov microwave oscillator without a guiding magnetic field

A relativistic Cherenkov microwave oscillator without a guiding magnetic field has been designed, constructed, and tested in which a continuous cylindrical electron beam propagates in a short (L ≈ 3λ, λ being the radiation wavelength) resonant slow-wave structure. The electron beam is energy-modulated at the input of the interaction space, which provides conditions for the energy exchange at a wave phase velocity exceeding the particle velocity. The effective beam-wave coupling is provided by a nearly homogeneous profile of the longitudinal electric field component of the synchronous wave in the interaction space cross section. The efficiency of power conversion from high-current electron beam to electromagnetic radiation at E₀₁ mode is about 8% at a maximum output pulse radiation power of 1.2 ± 0.3 GW and a working frequency of 4.05 GHz.     

The harmonic oscillator equation for ultracold neutrons moving in an inhomogeneous magnetic field

The motion of ultracold neutrons in a magnetic field featuring a quadratic inhomogeneity is considered. A partial solution to the stationary Schrödinger equation is found, which leads to a harmonic oscillator equation for the X coordinate. It is demonstrated that, under certain conditions, it is basically possible to provide for a spatial focusing of neutrons with the formation of either a single point focus or two side foci. Dependence of the focusing on the degree of monochromaticity of the neutron beam is considered.     

Chaotic oscillator with electron feedback and magnetic field at the cathode

The influence of a magnetic field at the cathode on the operation of a low-voltage vircator with electron feedback has been experimentally studied. It is shown that this magnetic field can significantly improve the characteristics and parameters of the vircator, provided that the field lines do not coincide with electron trajectories in the system.     

New phases of HTS in high magnetic field

Fluctuation behavior of HTS in high magnetic field is studied within the Ginzburg-Landau theory. Landau level degeneracy of Cooper pairs enhances fluctuations which destroy the familiar Abrikosov lattice. Instead, a charge density-wave of Cooper pairs (SCDW) is the new low-temperature phase of the theory. SCDW has no condensate, but differs from the normal state by a periodic modulation of Cooper pair density. In the presence of disorder, the Abrikosov state is revived and both superconducting and density-wave phases are possible.I would like to thank my collaborators I. F. Herbut, R. áik, and D. Stroud for many useful and productive discussions. The work reported here was supported in part by the NSF grant DMR-9415549.     

Optimizing nonstationary 38-GHz pulse-train relativistic backward wave oscillator with low guiding magnetic field

Characteristics of a compact relativistic backward wave oscillator (BWO) operating in the 8-mm wavelength range have been optimized using the results of experimental investigation and numerical simulations. The coefficient of electron beam power conversion into microwave pulses close to unity is obtained for electrons transported in inhomogeneous magnetic field (2.2–1.7 T) below the cyclotron resonance level. In a regime of train generation at a repetition frequency of 10 Hz, the peak power of ～250-ps electromagnetic pulses amounted to 450–600 MW. Numerical simulations show good prospects for obtaining peak powers above 100-MW level using a BWO with a beam-focusing system based on high-coercivity permanent magnets.     

A new model of DLA under high magnetic field

A new Monte Carlo model is introduced to describe diffusion-limited aggregation (DLA) with extra forces arising from Lorentz's and/or Coulomb forces. Furthermore, we simulate a behavior of multiparticle diffusive aggregation to examine the resultant pattern of crystal in electrochemical deposition. Different patterns grown under various external forces are produced by Monte Carlo simulations. In the present model, the basic movement of particles is a random walk, with different transition probabilities in different directions, which characterizes stochastically the effect of extra forces. In case of assuming a high magnetic field, pattern formations which are qualitatively different from the standard DLA model are observed and they are successfully compared with preexisting experiments (Mogi et al., 1991). The present numerical results of electrochemical deposition show that the generated patterns strongly depend on the force acting on ions and their concentration (Sawada et al., 1986).     

Transport of paramagnetic liquids under nonuniform high magnetic field

From recent investigations, the magnetic force generated by a heterogeneous high magnetic field has been highlighted, in particular by levitating systems. This paper is devoted to describing a new method for the analysis of the magnetic properties of liquids by using the magnetic force. This technique has consisted of observing and measuring the transport of a paramagnetic or diamagnetic liquid under the gradient of high magnetic fields. The theoretical approach of this phenomenon has been developed taking into account the fluid motion expanding in an axially symmetrical magnetic field. From this investigation, a typical experiment has been carried out by injecting a small amount of paramagnetic copper sulfate solution in a cell settled inside the bore of a superconducting magnet. Consequently, the accordance between the experimental results and the theoretical expectations has led to the determination of the magnetic susceptibility of the solution in a short time.     

强磁场下Al-Si过共晶合金组织细化原理研究

为了改善Al-Si合金性能,研究了强磁场对Al-Si过共晶合金组织的影响.依据热力学和晶粒形核理论,阐述了组织变化的原因.研究表明:当Al-Si过共晶合金在600℃施加强磁场并平行于磁场方向下凝固时,共晶组织被细化,但对初生硅相影响不大;磁场强度越大,细化效果越明显;强磁场降低了固态熵和磁自由能的影响,使共晶组织临界形核半径减小,而硅由于是逆磁质对其影响不大;强磁场使液态金属平行于磁场方向流动,进一步细化了组织.     

高低温循环试验下磁脉冲焊接接头性能研究

磁脉冲焊接是一种高效的固相焊接工艺,对异种金属材料在汽车轻量化中的运用具有积极意义.通过对5052Al/HC420LA板件磁脉冲焊接接头进行不同条件下的高低温循环试验,对比焊接接头在高低温循环试验前后的力学性能变化,研究了高低温循环冷却方式、循环次数对焊接接头性能的影响.利用扫描电子显微镜(SEM)研究了焊接接头微观形貌特征,分析了高低温循环试验前后焊缝微观界面的特征及其变化.研究表明：不同高低温循环试验条件下5052Al-HC420LA铝-钢磁脉冲焊接接头的连接强度相比于5052铝合金的母材强度下降了5%~25%;冷却速度越快,高低温循环次数越多,接头力学性能下降越明显;接头在高低温循环试验前后出现了母材失效与焊缝失效两种剪切失效模式;水冷冷却的接头比空冷冷却更易产生微观裂纹.     

Torsional oscillations of an anisotropic semi-infinite space by an impulsive twist in the presence of a magnetic field

We study magneto-elastic torsional oscillations of an orthotropic, homogeneous semi-infinite space by an impulsive twist applied over some circular region of the free boundary. Taking displacement currents into account, expressions for the elastic displacement, induced magnetic and electric fields in the half space and free space are calculated. The magnetic field acting is supposed to be uniform and normal to the free surface z = 0 and is directed into the medium. It is shown that torsional oscillations develop into shear waves at a large distance from the region of the applied twist in the radial direction. Further it turns out that, when compared with the case of zero displacement current the present case is found to decrease the phase velocity. Expressions for the real phase velocity, attenuation constant, phase angle and the skin depth of each of the two modes, which are predominantly elastic and magnetic in character, are calculated. Results are compared with those available in the literature for some special cases of shear waves in an infinite medium and electro-magnetic waves in conductors.     

稳态混合磁体装置低温系统过冷槽的设计与优化

40 T稳态混合磁体装置的外超导磁体需要4.5K、5×105Pa、18 g／s超临界氦迫流冷却,拟采用盘管换热器将从制冷机出来的氦冷却至超临界状态.首先对氦制冷机进行混合模式的热力学分析,确定过冷槽中盘管换热器的进口压力及温度,进而提出阶梯管径理论,根据工程要求设计并优化盘管换热器,得出盘管换热器的盘绕方式及尺寸;最后...     

稳态混合磁体15kA高温超导电流引线的设计

为了降低运行费用,正在建设中的中国科学院强磁场科学中心稳态混合磁体的电流引线采用高温超导电流引线.依据一种较为精确计算电流引线的方法,从传热学中的特征关联式出发,初步计算出了稳态混合磁体15 kA高温超导电流引线的基本尺寸与漏热.高温超导电流引线的常温段采用板式换热器的结构形式,增大了对流换热面积;超导段的保护体采用不锈钢,降低了对液氦热沉的热负荷.     

Neutron experiments on solid3He in high field at very low temperature

The magnetic transition from the paramagnetic phase to the magnetically ordered high-field phase of solid³He is observed by polarized neutron transmission experiments. The transition shows the feasibility of neutron diffraction experiments on the high-field ground state of solid³He. The behavior of the boundary resistance between solid³He and silver powder in a magnetic field is discussed.     

基于逐步回归法的潜艇高空磁场仿真

应用目前磁场换算中较多使用的磁荷模拟法对潜艇高空磁场进行了仿真，为了尽量减少磁荷的位置及大小受人为经验的影响，且提高换算精度，采用逐步回归法对各模拟磁荷的磁矩进行筛选，最后对潜艇高空磁场进行了计算机仿真．仿真结果表明，该方法精度比较高，而且模型的稳定性好，对实际防空中磁探具有重要的意义．     

高梯度强磁力永磁磁选机磁系的研究与磁场计算

用稀土永磁材料NdFeB,研究并设计了高梯度强磁力永磁磁选机的磁系,用我们推导的磁路计算方法及公式对磁系的磁场强度、梯度及磁力进行了计算与分析,研制并优选了最佳的高梯度强磁力永磁磁选机的磁系.     

Effect of high magnetic field on the processing of pearlitic steels

This paper compares data from various sources concerning the impact of high magnetic field (HMF) on changes that occur in pearlite with respect to microstructure, phase transition, and mechanical properties. HMF raises the transformation temperatures of both ferrite and pearlite. This effect can be enhanced by increasing the carbon content. Other alloying elements may influence austenite decomposition temperature, Curie temperature, and magnetic moment, thus either increasing or decreasing the effect of HMF on phase transformation temperature. By altering the transformation thermodynamics, HMF increases the volume fraction of proeutectoid ferrite, decreases that of cementite, and decreases the lamellar spacing. HMF introduces the microstructure anisotropy and aligns proeutectoid ferrite grains parallel to the direction of the HMF. This effect becomes smaller when the cooling rate is higher. By affecting both phase transformation and the alignment of grains, HMF affects the morphology and microstructure of proeutectic ferrite and pearlite, and, consequently, their mechanical properties and corrosion resistance.     

Duct flow with a transverse magnetic field at high Hartmann numbers

Finite element methods can be used for determining the flow in a straight channel under a variety of wall conductivity conditions when a uniform magnetic field is imposed perpendicular to the flow direction. At high Hartmann numbers oscillatory solutions are found unless sufficient points are placed within the Hartmann layers. In some one‐ and two‐dimensional problems it appears that it is adequate to place one or two points within the Hartmann layer to remove the oscillations. Central core values can sometimes be predicted with good accuracy even when the Hartmann layers are not resolved adequately. A nine‐point Gauss point rule has been used to evaluate the stiffness and other matrices for the eight‐node elements. Copyright © 2001 John Wiley & Sons, Ltd.     

Sub-100-nm negative bend resistance ballistic sensors for high spatial resolution magnetic field detection

We report the magnetic field detection properties of ballistic sensors utilizing the negative bend resistance of InSb∕In(1-x)Al(x)Sb quantum well cross junctions as a function of temperature and geometric size. We demonstrate that the maximum responsivity to magnetic field and its linearity increase as the critical device dimension is reduced. This observation deviates from the predictions of the classical billiard ball model unless significant diffuse boundary scattering is included. The smallest device studied has an active sensor area of 35×35 nm(2), with a maximum responsivity of 20 kΩ∕T, and a noise-equivalent field of 0.87μT∕Hz at 100 K.     

Sputter deposition of dielectric films using a magnetic field for protection from high energy electrons

Thin films of SiO₂ and Al₂O₃ were prepared by r.f. sputtering. For protection from energetic electrons in the plasma, deposition was carried out in an area protected by a magnetic field of appropriate strength.The deposited films are free of pinholes, show sound insulation characteristics and have good adhesion to the substrate.