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1.
临界电流密度Jc是超导薄膜的一个重要参量,它可以衡量超导薄膜的功率承载能力。大面积高温超导薄膜制成后,其Jc需要被无损精确测量。文中提出了一种新的交流磁场下的高温超导薄膜临界态模型:(1)基于此模型对薄膜的临界电流密度进行了精确无损测量;(2)并将实验测量的三次谐波电压曲线进行拟合研究。首先,根据麦克斯韦方程和伦敦方程,计算外加直流磁场超导薄膜Meissner态下电流和磁场在薄膜内的分布;然后分析薄膜进入临界态后内部电流的变化,在考虑顶扎力作用的情况下,提出了临界态电流和磁场非均匀分布模型;最后根据其模型,推导出三次谐波电压的表达式。为了验证该理论,分别对四片超导薄膜在不同频率下进行了三次谐波和临界电流密度测量。实验结果表明:三次谐波电压的理论与实验曲线一致;与四点传输法的测量结果相比较,该方法测量超导薄膜临界电流密度的误差在5%左右,具有高精度、无损伤、方便快捷等优点。 相似文献
2.
介绍了一种用于ITER的NbTi超导股线在不同温度下临界电流测试的方法和装置。该装置包括一孔径为70mm、最高磁场高达16T的背景磁体以及变温杜瓦等系统。对NbTi超导线变温测试设计了二元电流引线。用该系统得到了其NbTi超导股线在不同磁场不同温度下的临界电流,用“Luca”定标律拟合了测试结果,并对测试结果进行了分析。 相似文献
3.
We have measured the transport critical current densityJ
cof sintered YBa2Cu3O7, in various applied fields up to 185 Oe at 77 K. We find a sharp decay ofJ
cwith magnetic field. We show that this sharp decay is consistent with the low field hysteresis results of Groveret al. We argue that the observed field dependence is not caused by intragranular weak links. 相似文献
4.
K. Il’in D. Rall M. Siegel A. Engel A. Schilling A. Semenov H.-W. Huebers 《Physica C: Superconductivity and its Applications》2010,470(19):953-956
The density of critical currents jC in Nb thin films with thickness smaller than 15 nm and width between 100 nm and 10 μm has been measured in a wide temperature range. We have found that the temperature dependencies of jC in sub-micrometer wide bridges at 0.7TC < T < TC are well described by the Ginzburg–Landau de-pairing critical current. In wider bridges already at T < 0.9TC the jC value is significantly reduced due to the penetration and de-pinning of magnetic vortices. 相似文献
5.
在多晶系统的MgB2超导体中存在晶粒间较小的整体电流和晶粒内大的局域电流.用改变升温速率的方法制备了不同晶粒大小和晶粒连接性的MgB2样品,并对它们的晶粒大小进行了统计.采用一种测量超导临界电流密度的Campbell法,分别测量和计算得到了它们的整体电流和局域电流密度.研究表明:长时间的烧结造成晶粒变大,材料有较大的整体临界电流密度,而短时间烧结的样品则相反;同时发现晶粒细化只提高了样品的局域临界电流密度,而且样品内部缺陷、杂质及晶界等因素是影响MgB2超导体整体电流传输的主要因素. 相似文献
6.
We investigated the influence of surface damage on the critical current density (Jc) of MgB2 thin films via 140-keV Co-ion irradiation. The Jc(H) of the surface-damaged MgB2 films was remarkably improved in comparison with that of pristine films. The strong enhancement of Jc(H) caused by a surface damage in MgB2 films can be ascribed to additional point defects along with an atomic lattice displacement introduced through low-energy Co-ion irradiation, which is consistent with the change in the pinning mechanism, from weak collective pinning to strong plastic pinning. The irreversible magnetic field (Hirr) at 5 K for surface-damaged MgB2 films with a thickness of 850 and 1300 nm was increased by a factor of approximately 2 compared with that of a pristine film. These results show that the surface damage produced by low energy ion irradiation can serve as an effective pinning source to improve Jc(H) in a MgB2 superconductor. 相似文献
7.
Feng Shuang-jiu Chen Chun-xia Li Guang Li Xiao-guang 《Frontiers of Physics in China》2006,1(2):243-245
The dependences of critical current density J
c on the interlayer coupling strength and magnetic field in Bi2212 crystals were obtained by measuring the magnetic loop of
the crystals with different interlayer coupling strengths. It was revealed that J
c decreases with the decrease in the interlayer coupling of the crystals. The relation of J
c ∞ exp (−H
β) was also found in the crystals, and further analysis indicated that it was the result of Zeldov pinning potential model.
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Translated from Chinese Journal of Low Temperature Physics, 2005, 27(1) (in Chinese) 相似文献
8.
《Current Applied Physics》2014,14(9):1277-1281
We have investigated the critical current density for MgB2 films having various crystal orientations prepared by using a hybrid physical-chemical vapor deposition system. An enhancement of the critical current density is clearly presented in MgB2 films with an a-axis or a b-axis orientation rather than a c-axis orientation. X-ray diffraction patterns reveal a suppression of c-axis orientations while a (100) orientation becomes dominant, and the surface morphology of the a-axis-oriented film shows that the orientation of the c-axis-oriented MgB2 grains parallel to the plane of the substrate. As the a-axis orientation becomes more dominant in the MgB2 films, the field performance of the critical current density clearly becomes better. These results suggest that the synthesis of MgB2 with high ab-plane orientations is one of the keys to enhancing the critical current density in MgB2. 相似文献
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T. Sueyoshi S. Yutani T. Sogo K. Yonekura A. Adachi T. Fujiyoshi F. Mitsugi T. Ikegami N. Ishikawa S. Awaji K. Watanabe 《Physica C: Superconductivity and its Applications》2010,470(20):1295-1299
We investigated the dependences of the critical current density Jc on the magnetic field angle θ in YBa2Cu3O7−δ thin films with the crossed configurations of the columnar defects (CDs). To install the crossed CDs, the films were irradiated using the high energetic Xe ions at two angles relative to the c-axis. The additional peak around the c-axis appears in the Jc(θ) for all irradiated films. In lower magnetic fields, the height of the Jc(θ) peak caused by the crossed CDs with the crossing angles θi = ±10° was higher than that for the parallel CDs. It is considered that the correlation of the flux pinning by the crossed CDs along the c-axis occurs even in the case of θi = ±25°, which was also suggested by the kink behaviors of the scaling parameters of the current–voltage characteristics near 1/3 of the matching field. In higher magnetic fields, on the other hand, the height and width of the Jc(θ) peak for the crossed CD configurations rapidly reduce with increasing the magnetic field compared to the parallel ones. In the crossed CD configurations, the dispersion in the direction of CDs would prevent the correlation of flux pinning along the c-axis in high magnetic fields, which occurs in the parallel CD configurations due to the collective pinning of flux lines including the interstitial flux lines between the directly pinned flux lines by CDs. 相似文献
12.
基于Kim临界态模型,通过考虑超导块材内部屏蔽电流的穿透历史过程,讨论了场冷条件下临界电流密度对高温超导悬浮系统磁悬浮排斥力和吸引力的影响.结果显示:最大超导磁悬浮排斥力和吸引力均随临界电流密度的增加呈指数关系增加,并趋于饱和;场冷条件下的磁悬浮力回滞能量损耗远高于零场冷情况;存在一个磁悬浮力比率κ,κ值对于评价大电流... 相似文献
13.
A new analytical model of high voltage silicon on insulator (SOI) thin film devices 总被引:2,自引:0,他引:2
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A new analytical model of high voltage silicon on insulator (SOI)
thin film devices is proposed, and a formula of silicon critical
electric field is derived as a function of silicon film thickness by
solving a 2D Poisson equation from an effective ionization rate,
with a threshold energy taken into account for electron multiplying.
Unlike a conventional silicon critical electric field that is
constant and independent of silicon film thickness, the proposed
silicon critical electric field increases sharply with silicon film
thickness decreasing especially in the case of thin films, and can
come to 141V/μm at a film thickness of 0.1μm which is
much larger than the normal value of about 30V/μm. From the
proposed formula of silicon critical electric field, the expressions
of dielectric layer electric field and vertical breakdown voltage
(VB,V) are obtained. Based on the model, an ultra thin film
can be used to enhance dielectric layer electric field and so
increase vertical breakdown voltage for SOI devices because of its
high silicon critical electric field, and with a dielectric layer
thickness of 2μm the vertical breakdown voltages reach 852
and 300V for the silicon film thicknesses of 0.1 and 5μm,
respectively. In addition, a relation between dielectric layer
thickness and silicon film thickness is obtained, indicating a
minimum vertical breakdown voltage that should be avoided when an
SOI device is designed. 2D simulated results and some experimental
results are in good agreement with analytical results. 相似文献
14.
通过混合物理化学气相沉积法 (hybrid physical-chemical vapor deposition, HPCVD), 在(000l) SiC 衬底上制得一系列从10 nm到8 μm的MgB2超导膜样品, 并对它们的形貌、超导转变温度Tc 和临界电流密度Jc与膜厚度的关系进行了研究. 观察到Tc随膜厚度增加上升到最大值后, 尽管膜继续增厚, 但Tc值保持近乎平稳, 而Jc则先随膜厚度增加上升到最高值后, 继而则随膜的厚度的增加而下降. MgB2膜的Tc(0)和Tc(onset)值与膜厚的关系基本一致, Tc(0)在膜厚为230 nm处达到最大值Tc(0)=41.4 K, 而Jc(5K,0T)在膜厚为100 nm时达到最大值, Jc (5 K, 0 T)=2.3×108A·cm-2, 这也说明了我们能用HPCVD方法制备出高质量干净MgB2超导膜. 本文研究的超导膜厚度变化跨度非常大, 从10 nm级的超薄膜到100 nm级的薄膜, 再到几微米的厚膜, 如此Tc和Jc对膜厚度变化的依赖就有了较完整、成体系的研究. 并且本文的工作对MgB2超导薄膜制备的厚度选取具有实际应用意义.
关键词:
2超导膜')" href="#">MgB2超导膜
混合物理化学气相沉积法
厚度
临界电流密度 相似文献
15.
M. Gitterman I. ShapiroB.Ya. Shapiro 《Physica C: Superconductivity and its Applications》2012,472(1):83-86
In a nonuniform superconductor with randomly distributed local critical temperature both the macroscopic critical temperature and the upper critical magnetic field strongly depend on the characteristic correlation length ρ0 of correlated disorder. The shift of the macroscopic critical parameters from those for non-correlated disorder, which does not exist for white noise, is obtained for small ρ0 in the framework of the Ginzburg-Landau theory. 相似文献
16.
S.K. Chen X. Xu J.H. Kim S.X. Dou J.L. MacManus-Driscoll 《Physica C: Superconductivity and its Applications》2010,470(20):1211-1215
In this work, nano sized SiC powders were mixed with Mg and B and reacted by either a one-step insitu or two-step method resulted in different level of C substitution. X-ray diffraction shows the presence of Mg2Si signifying that the reaction between SiC and Mg occurred leading to the release of C in samples reacted in one-step method. Moreover, the much reduced value of a-axis indicates C substitution took place. Resistivity measurements showed higher intragrain scattering owing to a higher density of defects and/or impurities. These samples also show higher Hirr and Hc2 at 20 K in comparison to samples with mainly unreacted SiC (hence lower C substitution). More importantly, their Jc’s are more insensitive to high magnetic field (>4 T) at 6 K. However, at 20 K the effect of C content on Jc(H) is less pronounced. Finally, the order of magnitude of Jc(H) at both 6 K and 20 K is rather dominated by pinning. 相似文献
17.
YBa2Cu3O7 + xAg?(x = 0.0, ?5.0, ?15.0 and 20 wt%) composite samples have been prepared by the solid state reaction method. The changes in structure are confirmed from the X-ray diffraction analysis and SEM measurements. The critical current density is calculated using Bean's formula from the magnetization measurement. We find that the addition of silver in YBCO enhances the critical current density (?JC) by a factor of nearly six (for 15% Ag) in comparison to pure YBCO. Enhancement of the pinning force (FP) by a factor of ten is also reported. The enhancement in ?JC is investigated over a wide range of magnetic fields. These significant changes in ?JC and FP are attributed to the presence of Ag particles as efficient artifical pinning centers in YBCO. 相似文献
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根据脉冲驱动源和负载参数,提出了3 MV感应电压叠加器磁感应腔的设计指标为1.2 MV/70 ns。由感应腔的电流传输效率和真空同轴线绝缘要求,确定了磁芯的几何尺寸;研制了矩形比为0.5的预退火非晶磁环,明确磁环数量不少于6只;在30 T/s时,实验测量的最大脉冲相对磁导率与饱和波模型计算结果相当;估算磁感应腔的等效激磁电感约为7.3 μH,涡流损耗电阻约为139 Ω。根据临界击穿场强的经验公式,采用电场数值分析方法,确定了磁感应腔的电气结构;实验验证了磁感应腔设计有效性;建立了基于磁感应腔的3 MV感应电压叠加器全电路模型,阳极杆箍缩二极管电压、电流计算波形,与实验结果基本相符。 相似文献