电子成像均匀约束磁场的产生及测试分析

为增加离子与原子碰撞成像系统中探测电子的立体角，设计了一约束电子的复合型亥姆霍兹线圈装置.对复合型亥姆霍兹线圈的磁场分布进行了理论计算和分析，并对制作的复合型亥姆赫兹线圈产生的磁场进行了实验测量，得出磁场的均匀性好于±0.6%. 关键词： 亥姆霍兹线圈 磁场分布 磁场均匀性     

地磁环境下基于SQUID三轴磁强计的矢量稳场

超导量子干涉器件(Superconducting Quantum Interference Device, 简称 SQUID) 是一种高灵敏度的矢量磁探测器. 本文采用低温超导SQUID 作为传感器, 搭建了一套三轴矢量磁场稳定装置. 该系统由两个三轴 SQUID磁强计模块、 比例积分微分(PID) 控制器和反馈线圈组组成. 在该系统的矢量稳场下, 磁场波动峰峰值在有效带宽内可以降低四个数量级, 可达pT 量级, 稳场效果显著. 此技术可以满足大部分需要稳定磁场, 如高灵敏度磁传感器的标定等应用场合.     

基于电磁感应法测量亥姆霍兹线圈磁场的改进

本文在电磁感应法的基础上,通过与亥姆霍兹线圈串联使电容达到谐振的改进方法,测量了不同电容参数下的亥姆霍兹线圈磁场分布,并利用Origin软件拟合分析了亥姆霍兹线圈磁场与中心轴线位置的关系.实验结果表明,基于电磁感应的改进方法测得的亥姆霍兹线圈磁场精确度在一定程度上均大于传统电磁感应法的测量结果,3种电容选择中,串联电容为0.099×10^-6F时,精确度最高,拟合的亥姆霍兹线圈磁场与中心轴线位置的关系式与理论状态下的公式基本吻合.改进方法的实验效果明显,精确度高,科学可行,是一种值得推广的测量亥姆霍兹线圈磁场的改进方法.     

亥姆霍兹线圈磁场均匀性的研究

本文利用ＩＢＭ—ＰＣ计算机时圆电流的磁场和亥姆霍兹线圈（Ｎ＝１和Ｎ＝９９）的磁场作了精确计算； 给出了亥姆霍兹线圈的磁场系数和相对误差的数据，画出了１％、０．２％和０．０２％的磁场均匀区；对影响亥姆霍兹线圈磁场均匀性的几个因素进行了计算和讨论．     

亥姆霍兹线圈最均匀磁场的条件

亥姆霍兹线圈最均匀磁场的条件孟立志，赵保利（内蒙古大学０１００２１）（内蒙古林学院０１００１９）亥姆霍兹线圈是由一对相互平行的半径相等的圆线圈所构成．根据毕奥一萨伐尔定律，电流元Ｉｄｌ在空间产生的磁场ｄＢ为［１］根据（１）式，很容易得到一个圆线圈在其...     

HT_c SQUID工作环境低频磁干扰消除研究

针对高温超导量子干涉器(HT_c SQUID)磁强计技术在非磁屏蔽环境中受到的极低频干扰,实验研究了主动补偿方法消除这种干扰的可行性和有效性。实验由高精度程控电流源提供电流,通过亥姆赫兹线圈产生用于抵消极低频干扰的补偿磁场,使用两套HT_c SQUID磁强计搭建了测试系统,其中一套用于低频磁干扰背景的探测,另一套用于磁干扰补偿消除效果的甄别。结果表明,这种动态补偿消除方法可以达到比较好的效果。     

低噪声超导量子干涉器件磁强计设计与制备

超导量子干涉器件(superconducting quantum interference device, SQUID)作为一种极灵敏的磁通传感器,在生物磁探测、低场核磁共振、地球物理等领域得到广泛应用.本文介绍了一种基于SQUID的高灵敏度磁强计,由SQUID和一组磁通变压器组成. SQUID采用一阶梯度构型,增强其抗干扰性.磁通变压器由多匝螺旋的输入线圈和大尺寸单匝探测线圈组成,其中输入线圈与SQUID通过互感进行磁通耦合.利用自主工艺平台,在4英寸硅衬底上完成了基于Nb/Al-AlO_x/Nb约瑟夫森隧道结的SQUID磁强计制备.低温测试结果显示,该磁强计磁场灵敏度为0.36 nT/Φ_0,白噪声段磁通噪声为8μΦ_0/√Hz,等效磁场噪声为2.88 fT/√Hz.     

亥姆霍兹线圈轴线磁场计算机测量实验研究

亥姆霍兹线圈产生的磁场具有广泛的物理应用。利用霍尔传感器件,研究制作了具有USB2．0数据通讯接口的高速磁场数据测量装置,编写了磁场数据采集处理程序,设计了中心距可调的亥姆霍兹线圈并用所研制的仪器进行了轴向磁场分布测量。结果表明：该实验装置测量精度高,实时性好,实验手段先进,可扩展为多个设计性物理实验。     

高阶高温超导量子干涉器件平面式梯度计的设计

设计了一种高温超导平面式梯度计的探测线圈，利用这种探测线圈与超导量子干涉器件(SQ UID)耦合，可以制成二阶或更高阶的高温超导SQUID平面式磁场梯度计.设计的探测线 圈由两个闭合环路组成，每个闭合环路是由若干个环路通过细小的连接通道连接而成.两个 闭合环路由一条超导窄带分割，将SQUID与这条超导窄带耦合可以测出超导窄带上的电流大 小.通过调整各个环路的形状、面积和位置，可以使超导窄带上的电流与磁场的高阶梯度成 正比，从而测得磁场的高阶梯度. 通过计算，得到了各个环路的面积、电感以及位置的关 系，在理 关键词： 高阶平面式磁场梯度计 高温超导薄膜     

超导量子干涉器件

超导现象是一种宏观量子现象.磁通量子化和约瑟夫森效应是两个最能体现这种宏观量子特性的物理现象.超导量子干涉器件(superconducting quantum interference device,SQUID)是利用这两个特性而形成的超导器件.SQUID器件在磁信号灵敏探测方面具有广泛的应用.本文简要介绍低温超导和高温超导SQUID器件的相关背景和发展现状以及应用领域.     

An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils

For a practical superconducting quantum interference device(SQUID) based measurement system,the Tesla/volt coefficient must be accurately calibrated.In this paper,we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils.The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil.By applying magnetic fields through a three-dimensional Helmholtz coil,the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields.Calibration with alternating current(AC) field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current(DC) calibration to avoid possible effects due to eddy current.In our experiment,a calibration relative error of about 6.89 × 10-4is obtained,and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils.The method does not need precise alignment of the magnetometer inside the Helmholtz coil.It can be used for the multichannel magnetometer system calibration effectively and accurately.     

基于拉曼频移的白宝石压腔无压标系统高温高压实验标定

在高压实验科学中, 各类宝石压腔是最为常见的高压设备之一, 其样品腔中压力的精确标定是实验的关键. 目前, 人们主要通过加入红宝石等压标物质来进行定压, 但压标物质的加入会增加实验的装样难度, 改变样品腔中的物理化学环境, 甚至直接与实验样品发生反应, 从而对实验结果产生影响. 在0–6.3 GPa和300–573 K下, 利用共聚焦拉曼显微镜, 根据白宝石压砧砧面的ν₁₂ 拉曼频移与温度和压力的变化关系, 建立了一套适用于高温高压水热体系的无压标白宝石压腔系统. 实验结果表明: 白宝石砧面的ν₁₂ 峰随着压力的升高发生线性蓝移, 而随着温度升高则发生线性红移, 且温度和压力对拉曼频移的影响存在耦合效应. 利用本实验结果, 可在高温高压下根据白宝石砧面的拉曼频移计算出样品腔的压力P=(Δλ-0.01913×ΔT)/(1.9158-0.00105×ΔT), 在物理学、材料学和地球科学等领域具有重要应用.     

一类演化方程的高稳定性的差分格式

考虑一类演化方程u_t=au∂_2k+1(其中a是常数,u∂_2k+1=∂^2k+1u/∂x^2k+1,k=1,2……)的有限差分解法。构造了两类具有高稳定性的显式差分格式。并用引入耗散项的方法建立了两类半显式差分格式,它们是无条件稳定的且可显式地进行计算。     

Development of series SQUID array with on-chip filter for TES detector

A cold preamplifier based on superconducting quantum interference devices(SQUIDs)is currently the preferred readout technology for the low-noise transition edge sensor(TES).In this work,we have designed and fabricated a series SQUID array(SSA)amplifier for the TES detector readout circuit.In this SSA amplifier,each SQUID cell is composed of a first-order gradiometer formed using two equally large square washers,and an on-chip low pass filter(LPF)as a radiofrequency(RF)choke has been developed to reduce the Josephson oscillation interference between individual SQUID cells.In addition,a highly symmetric layout has been designed carefully to provide a fully consistent embedded electromagnetic environment and achieve coherent flux operation.The measured results show smooth V-Φcharacteristics and a swing voltage that increases linearly with increasing SQUID cell number N.A white flux noise level as low as 0.28μφ;/Hz;is achieved at 0.1 K,corresponding to a low current noise level of 7 pA/Hz;.We analyze the measured noise contribution at mK-scale temperatures and find that the dominant noise derives from a combination of the SSA intrinsic noise and the equivalent current noise of the room temperature electronics.     

Development of 1.3GHz high-T-c rf SQUID

A new high-T_c (HT_c) rf SQUID working at around 1.3GHz has been developed to avoid electromagnetic interference such as growing mobile communication jamming. This new system works in a frequency range from 1.23 to 1.42GHz (centred at 1.3GHz), which is not occupied by commercial communication. The sensor used in the 1.3GHz rf SQUID is made of a HT_c coplanar superconducting resonator and a large-area HT_c superconducting film concentrator. We have achieved in the 1.3GHz HT_c rf SQUID system a minimal flux noise of 2.5×10^{-5}Φ_0/\sqrt{Hz} and a magnetic field sensitivity of 38fT/\sqrt{Hz} in white noise range, respectively. The effective area of the concentrator fabricated on a 15×15mm^2 substrate is 1.35mm^2. It is shown that the 1.3GHz rf SQUID system has a high field sensitivity. Design and implementation of 1.3GHz HT_c rf SQUID offers a promising direction of rf SQUID development for higher working frequency ranges.     

A Superconducting Quantum Interference Device Measurement System for Ultra Low-Field Nuclear Magnetic Resonance

We describe a superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) spectrometer operating at ultralow magnetic fields far below the Earth’s field. The spectrometer consists of a helium-cooled magnetic sensor system and two Helmholtz coils, one for pre-polarizing the sample by fields of up to 5 mT, and one for the detection in fields of the nanotesla and microtesla range. The spectrometer represents the current state of the art in ultralow-field NMR and enables the observation of phenomena that are difficult or impossible to achieve by a conventional NMR setting. In particular, one can obtain broad band spectra covering different nuclei, such as ¹H and ³¹P, with a frequency resolution in the millihertz range, observe the variation of their heteronuclear coupling with the detection field strength, and investigate relaxation processes that reflect molecular dynamics in the millisecond range.     

Superconducting phase qubits with shadow-evaporated Josephson junctions

We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device(SQUID) detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm~2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems(TLS) residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T_1 and dephasing time T_φ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.     

Implementation of quantum partial search with superconducting quantum interference device qudits in cavity QED

We present a method to implement the quantum partial search of the database separated into any number of blocks with qudits,D-level quantum systems.Compared with the partial search using qubits,our method needs fewer iteration steps and uses the carriers of the information more economically.To illustrate how to realize the idea with concrete physical systems,we propose a scheme to carry out a twelve-dimensional partial search of the database partitioned into three blocks with superconducting quantum interference devices(SQUIDs)in cavity QED.Through the appropriate modulation of the amplitudes of the microwave pulses,the scheme can overcome the non-identity of the cavity–SQUID coupling strengths due to the parameter variations resulting from the fabrication processes.Numerical simulation under the influence of the cavity and SQUID decays shows that the scheme could be achieved efficiently within current state-of-the-art technology.     

Modulation depth of series SQUIDs modified by Josephson junction area

The superconducting quantum interference device(SQUID) amplifier is widely used in the field of weak signal detection for its low input impedance, low noise, and low power consumption. In this paper, the SQUIDs with identical junctions and the series SQUIDs with different junctions were successfully fabricated. The Nb/Al-AlO_x/Nb trilayer and input Nb coils were prepared by asputtering equipment. The SQUID devices were prepared by a sputtering and the lift-off method.Investigations by AFM, OM and SEM revealed the morphology and roughness of the Nb films and Nb/Al-AlO_x/Nb trilayer.In addition, the current–voltage characteristics of the SQUID devices with identical junction and different junction areas were measured at 2.5 K in the He~3 refrigerator. The results show that the SQUID modulation depth is obviously affected by the junction area. The modulation depth obviously increases with the increase of the junction area in a certain range. It is found that the series SQUID with identical junction area has a transimpedance gain of 58 ? approximately.     

拟随机选择法

本文针对通常的随机选择法在求Riemann问题基本解上遇到的困难,提出采用拟特征线形式下的各独立标量方程形式,求其简单的Riemann问题组以代替原Riemann问题的解。这样,使方法基本保持了随机选择法的特点,又使方法的实现、应用和推广更加容易,而且可以设计并行算法。最后用激波管和溃坝问题为例作了实算。结果与已知的结果相比也是满意的。