共查询到19条相似文献,搜索用时 234 毫秒
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亥姆霍兹线圈在产生数十T的准静态脉冲磁场的装置中得到广泛应用。以自行研制的一套用于磁压剪实验技术的脉冲磁场发生系统的亥姆霍兹线圈为研究对象,结合装置的电参数,利用有限元软件ANSYS对装置放电过程中线圈的热和力进行了仿真研究。研究结果表明,当装置在线圈中产生上升时间约1.34 ms、幅值14.37 kA的放电电流和10.7 T的磁场时,线圈中的最大温升约150℃,最大应力近0.5 GPa,铜导线中的最大应力约0.2 GPa,线圈导线变形位移小于0.05 mm。基于分析结果,在线圈制作时,选择绝缘层耐温超过200℃、抗拉强度0.5 GPa的铜导线作为线圈绕线,选择抗拉强度达5.8 GPa的柴龙纤维绕制在铜导线外层进行加固,并制作了相应结构的亥姆霍兹线圈对。利用该线圈对进行的放电实验测试结果表明,在满足设计指标的情况下,线圈对结实可靠,可重复使用。 相似文献
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对Ka波段TM02模式低磁场相对论返波管的结构特点、工作原理进行了介绍,详细分析了该器件以TM02模工作的模式选择机制。通过粒子模拟,该器件在1 T引导磁场下获得了功率为493 MW、频率29.3 GHz的微波输出,工作模式及频率与理论设计相一致。随后,基于模拟中的结构参数开展了初步的实验研究,当二极管电压为580 kV、电流为3.56 kA、引导磁场1 T时,获得了功率286 MW、频率29.3 GHz、脉宽约10 ns的微波输出。实验获得的微波频率与数值模拟一致,但是微波功率与数值模拟结果有明显差异,并且微波脉冲后沿有明显的缩短,分析认为在低磁场下后端谐振腔链受到电子轰击是导致该问题的主要原因。 相似文献
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分析和测试了磁致伸缩材料磁弹性内耗的偏置磁场依赖特性,发现Terfenol-D的品质因数(与内耗的量值成反比)强依赖于偏置磁场.利用磁致伸缩材料磁弹性内耗强依赖于偏置磁场的特性,提出了一种静态和准静态磁场的磁传感器方法,即将磁致伸缩材料与压电变压器单元层叠构建一种复合变压器.分析表明:在谐振状态下,复合变压器的输出电压正比于其品质因数,于是复合变压器的输出电压强依赖于偏置磁场;磁致伸缩材料的ΔE效应对复合变压器输出电压的影响很小.制备Terfenol-D/PZT8复合变压器进行了实验,结果表明,在近谐振状态下,当激励输入电压振幅为0.5V时,复合变压器工作的输出电压对静态磁场的灵敏度达到~5.12mV.Oe-1. 相似文献
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研究了行波管中均匀聚焦磁场和周期永磁聚焦磁场对轨迹波动的影响。推导了这两种磁场下轨迹波动周期和幅值,讨论了磁场强度对轨迹的影响。解释了聚焦磁场存在小的波动的原因,并且通过计算得出小波动的周期为磁场周期的1/2,揭示了在周期永磁聚焦磁场下,电子轨迹近似等效于周期为周期永磁聚焦磁场1/2的小波动和均匀磁场形成的波动轨迹的叠加。利用电子科技大学编写的微波管模拟套装中的3维注-波互作用模块进行了静态轨迹计算,验证了理论推导。 相似文献
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利用PIC(particle-in-cell)方法模拟研究了超短强激光与锥型三明治结构靶相互作用快电子束的产生和传输,并与锥通道靶、锥丝靶和锥靶在相同激光参数下的作用结果进行了比较.研究发现强激光与锥三明治靶作用产生的快电子能被不同密度材料产生的准静态界面强磁场有效地准直传输.相对其他三种锥型结构靶,锥三明治靶能产生更多数目及更高能量的快电子,提高了激光到快电子的能量转换效率和快电子束的品质,这对快点火能量沉积是有利的. 相似文献
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三维拉曼边带冷却后的铯原子样品装载于一个磁悬浮的大体积交叉光学偶极阱中, 继续加载一个小体积的光学偶极阱后, 实现了Dimple光学偶极阱对铯原子的高效装载. 对不同磁场下磁悬浮大体积光阱的有效装载势能进行理论分析与实验测量, 得出最优化的梯度磁场和均匀偏置磁场, 获得了基于磁悬浮大体积光阱的Dimple光学偶极阱的装载势能曲线, 实现了Dimple光学偶极阱对经拉曼边带冷却后俘获在磁悬浮的大体积光阱中的铯原子样品的有效装载. 比较了Dimple光学偶极阱分别从拉曼边带冷却、大体积的交叉光阱和消除反俘获势后的磁悬浮大体积光阱装载的结果, 将俘获在磁悬浮大体积光阱中的铯原子样品装载到Dimple光学偶极阱, 铯原子样品的密度提高了约15倍. 相似文献
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通过对层流平衡相对论电子的运动微分方程组进行数值求解,得到正则角动量在pθ=0,pθ=const.和pθ∝r2三种情况下,束流的传输特性.针对pθ=0的相对论实心电子束,利用数值求解得到了与解析方法一致的结果,从而验证了数值方法的合理性;针对无法用解析方法求解的pθ=0环行电子束、pθ=const.和pθ∝r2的情况,利用数值方法得到了束流和空间极限电流关于波导、电子束结构和二极管电压等参数的变化规律及对轴向导引磁场的要求.计算结果表明:当相对论电子束以层流平衡态传输时,环行束较实心束具有更高的空间极限电流和更低的轴向导引磁场,且当阴极发射面与导引磁场的磁场线垂直时,维持电子束层流平衡所需的轴向导引磁场最低;电子束在有限磁场导引下以层流平衡态传输时,空间极限电流明显大于无限大磁场导引下一维近似的情况.利用数值方法对层流平衡相对论电子束进行理论研究,更全面地揭示了电子束在正则角动量满足不同条件时的束流特性,为设计新型结构的高功率微波器件提供理论参考. 相似文献
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扩展互作用器件,采用三个线圈和一个磁极实现均匀磁场分布。根据理论计算采用有限元法磁学(FEMM)仿真软件对所求磁场进行了建模分析,依据FEMM计算的磁场结合静电电子枪,采用CST仿真软件对高电流密度、高压缩比的电子注在均匀聚焦磁场的作用下传输进行优化。经过计算得出,在工作电压为17 kV、阴极发射电流密度小于10 A/cm2的条件下,由皮尔斯电子枪发射的电子注在均匀磁场的聚焦作用下传输良好,通过率为100%,得到了导流系数为0.175μP的电子枪,在均匀磁场区形成了高电流密度、高压缩比的电子注,平均电流密度达到343.17 A/cm2,压缩比为32,电子注横纵速度比为7.2%。 相似文献
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P. Cantillon-Murphy L.L. Wald M. Zahn 《Journal of magnetism and magnetic materials》2010,322(17):2607-2617
In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad s−1. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 °C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B0. Results are presented for the expected temperature increase in small tumors ( radius) over an appropriate range of magnetic fluid concentrations (0.002-0.01 solid volume fraction) and nanoparticle radii (1-10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful the goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the transverse rotating magnetic field in the presence of B0 are investigated to demonstrate the effect of Ω, the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ. The analysis shows that as the rotating field frequency increases so that Ωτ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization's magnitude is a strong function of the field frequency. In this frequency range, the fluid's transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1-3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle spin-velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations. 相似文献
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P. Holstein J. Rauchfuß M. Winkler G. Klotzsche D. Geschke 《Solid state nuclear magnetic resonance》1998,10(4):225-233
Solid state NMR techniques have been developed to investigate dynamic molecular effects (e.g., molecular reorientations) due to simultaneously applied external electric fields on electrically sensitive materials such as liquid crystals (LC), liquid crystalline polymers (LCP) and polymeric electrets. Such effects can be observed only on relatively thin systems (10-200 μm). That means that many scans are necessary to achieve a sufficiently high signal-to-noise-ratio in the spectra (500-1000 scans). If the material is also magnetically sensitive, the electric field can be used to orient molecules in a starting orientational state and by switching-off the voltage to access fast reorientation processes in the magnetic field B0. Until now, the behaviour of orientable molecular systems under the influence of electric fields has been investigated by means of a more or less quasistatic approach (LCP: 100 V, electrets: 1 kV) in equilibrium states. The achievable time resolution depends on the desired signal-to-noise-ratio. For the case of proton NMR this means a time resolution of about 10 min. However, very often switching processes occur on a much shorter time scale. Using conventional techniques it is impossible to observe fast (ca. 100 μs) electrically or magnetically induced reorientation processes. In this work, we present a concept to overcome the problems outlined above and to extend the area of our current in situ NMR investigations on thin electrically-switched or poled polymeric layers. The basic idea is to include synchronized electric pulses during the NMR experiment using the preparation and/or mixing periods of a 1D or 2D pulse sequence for the application of an orienting field (electric or magnetic) and to use the reversibility of the molecular switching phenomenon to achieve a sufficient signal-to-noise-ratio. The techniques extend the range of possible investigations from about 100 μs to approximately T1 for correlated spectra (and to longer times of applied fields for uncorrelated spectra). Results are shown for a nematic LC and a nematic polymer having a similar side chain. 相似文献
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为了增强等离子体激励器的扰动能力、提升等离子体气动激励的控制效果,采用高压探针、烟流显示和PIV流场测试等多种研究手段,开展了磁场加速等离子体激励器特性研究,获得了激励器不同时刻的放电图像,分析了磁场强度对激励器电学特性与诱导流场特性的影响规律.结果表明,(1)放电等离子体的定向运动速度与磁场强度成正比,磁加速等离子体的最大移动速度达到了6 m/s;(2)通过对不同剖面的诱导流场进行研究发现,磁场加速等离子体激励器能够在近壁区产生一系列涡结构.此外,该诱导流场具有显著的三维特征与非定常特性.研究结果为开展基于磁加速等离子体气动激励的流动控制奠定了基础. 相似文献
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对大回旋半径电子枪的渐变线圈磁场进行了设计,采用3个线圈实现所需要的渐变磁场分布,增加了线圈磁场系统的调节能力,理论和计算机仿真的磁场分布结果符合得很好。将实现的渐变磁场分布同给定的静电场分布相结合,通过求解带电粒子的运动方程得到了粒子轨迹,在此基础上建立大回旋半径电子枪的3维粒子仿真模型,在给定静电场分布条件下分析了3个线圈安匝数对电子束参数的影响,完成了工作电压为40 kV、工作电流为1 A的大回旋半径电子枪的参数优化,得到了横纵速度比为1.4~2.5,纵向速度离散小于8%(横纵速度比为1.9时)的大回旋半径电子束。 相似文献