共查询到18条相似文献，搜索用时 453 毫秒
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结合光抽运铯束频标的具体结构,论证了用余弦傅里叶逆变换的方法推导原子速度分布的可行性;用该理论对实验系统测量的Ramsey花样进行了分析,得到铯束管中有效原子真实的速度分布,该速度分布与铯束管的具体结构对速度的要求相一致;通过速度分布精确计算了影响光抽运铯束频标准确度的重要因素——二级多普勒频移,其大小为-3．5×10-13。 相似文献
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本文指出了子午环光栏自动控制系统研制的必要性，并简要介绍了控制原理，结果表明，该控制部分设计合理大大简便了操作。 相似文献
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对太阳大气磁场的可靠测量有助于人们更好地理解太阳活动区内外的许多活动现象,如耀斑的触发和能量释放过程、黑子的形态和黑子大气的平衡、日珥的形成等.由于原子在磁场中的一些能级会产生分裂(Zeeman效应),使对应这些能级的谱线分裂成若干个具有不同偏振特性的分量,因此目前对黑子磁场的测量主要是通过偏振光,即Stokes参量I、Q、U、V的观测来实现的.该文主要介绍近30年来太阳黑子光谱反演的方法以及所取得的成就;同时也对光谱反演和滤光器型的望远镜矢量磁场的测量进行了简单的比较. 相似文献
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《天文研究与技术》2020,(3)
星载氢原子钟具有频率稳定度高、频率漂移率低的优点,在卫星导航定位和频率计量中得到了广泛应用。星载氢原子钟的腔泡系统用于实现氢原子的量子跃迁及其信号采集,原子跃迁信号幅度直接决定了系统的信噪比,进而影响整机性能指标,所以腔泡系统是星载氢原子钟的核心组件。目前,星载氢原子钟腔泡系统主要采用直螺线管来产生原子跃迁所需的C场。由于星载氢原子钟物理部分的结构限制,直螺线管的磁场均匀度有进一步提高的空间。探讨使用多段线圈代替直螺线管用于产生C场的可行性。首先对多段线圈产生的磁场进行理论分析计算,同时使用ANSYS电磁场仿真软件对多段线圈的各项参数进行仿真和优化,包括各段长度、段数、间距以及匝数、内径和总长度等。然后优选磁场均匀度较好的线圈配置参数,可将C场的非均匀度由直螺线管约10%降低到多段线圈约1%。根据仿真优化结果建立了试验九段线圈,对比测试了原子跃迁信号增益,同时结合电路部分进行闭环测试,对频率稳定度指标进行了对比。实验结果表明,原子跃迁信号可有效提升,阿伦方差在中短稳(1～1 000 s)表现更好。此项工作为星载氢原子钟整机性能指标的进一步提升打下了基础。 相似文献
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本文指出了子午环光栏自动控制系统研制的必要性，并简要介绍了控制原理．结果表明，该控制部分设计合理大大简便了操作． 相似文献
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介绍了光抽运铯束管的光频移测量的原理和结果，并对结果进行了简要的分析，估算了射入Ramsey腔的相应光强。产生散射光光频移的原因是抽运光和检测光通过漫反射进入微波腔的漂移区与铯原子相互作用所致。 相似文献
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为降低氢脉泽由C场不均匀导致的跃迁频率相对变化率,提出了三段螺线管和四组线圈两种C场组件设计方式。利用轴线上磁场的高阶展式计算了L=0.05～0.5的三段螺线管构造匀强磁场时的安匝比以及螺线管间距,并选择L=0.2～0.45的三段螺线管进行了磁场的有限元分析,给出了不同宽度的三段螺线管磁场非均匀度分布。其中L=0.45的三段螺线管在储存泡区域的最大非均匀度为0.105%,相应的跃迁频率相对变化率为1.02×10-13。采用相同的方法计算了四组线圈以及五组线圈构造匀强磁场时线圈间的安匝比和间距,并对线圈内的磁场进行了有限元仿真,给出了非均匀度分布,四组线圈式C场筒内磁场在储存泡区域的非均匀度最大值为0.066%,相应的跃迁频率相对变化率为6.42×10-14。 相似文献
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V. E. Abramov-Maksimov G. F. Vyalshin G. B. Gelfreikh V. I. Shatilov 《Solar physics》1996,164(1-2):333-343
In the present paper we present the results of measurement of magnetic fields in some sunspots at different heights in the solar atmosphere, based on simultaneous optical and radio measurements. The optical measurements were made by traditional photographic spectral observations of Zeeman splitting in a number of spectral lines originating at different heights in the solar photosphere and chromosphere. Radio observations of the spectra and polarization of the sunspot - associated sources were made in the wavelength range of 2–4 cm using large reflector-type radio telescope RATAN-600. The magnetic field penetrating the hot regions of the solar atmosphere were found from the shortest wavelength of generation of thermal cyclotron emission (presumably in the third harmonic of electron gyrofrequency). For all the eight cases under consideration we have found that magnetic field first drops with height, increases from the photosphere to lower chromosphere, and then decreases again as we proceed to higher chromosphere and chromosphere-corona transition region. Radio measurements were found to be well correlated with optical measurements of magnetic fields for the same sunspot. An alternative interpretation implies that different lines used for magnetic field measurements refer to different locations on the solar surface. If this is the case, then the inversion in vertical gradients of magnetic fields may not exist above the sunspots. Possible sources of systematic and random errors are also discussed. 相似文献
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Yu. V. Glagolevskij A. V. Shavrina G. A. Chuntonov D. A. Lyashko 《Astrophysical Bulletin》2013,68(4):454-460
Modelling the magnetic field structure in HD49976, we obtained a map of its magnetic field distribution on the surface and its main parameters. Simulating the distribution of Ca and Sr by the phase dependences of the Ca II 3934 Å and Sr II 4215 Å equivalent line widths revealed that their abundances are most likely increased between the magnetic poles. An insufficiently clear result is due to the structure of the magnetic field of HD49976, which proved to be complex, not corresponding to the central dipole. It is modelled by two dipoles, the stronger of them is in the center of the star, and the other, weaker, is at distance of 0.3R * from the center. The synthetic spectrum method yielded abundances of 28 elements in the moments of magnetic field extrema. The carbon and sulfur abundances proved to be close to the solar values, silicon showed a deficit of 1.0 dex, lithium, calcium, iron and the iron peak elements, strontium, rare earths are in excess, especially significant in the case of rare earths. High-resolution spectropolarimetric observations closely covering the entire rotation period are required to investigate the distribution of chemical elements in complex multi-dipole magnetic configurations, applying the Magnetic Doppler Imaging method. 相似文献
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Magnetic reconnection induced by Kelvin Helmholtz instability 总被引：1，自引：0，他引：1
MHD simulation study is performed to investigate magnetic reconnection induced by the Kelvin Helmholtz instability in the initially sheared magnetic field geometry as well as in the uniform magnetic field geometry. Slow mode rarefaction structures seen in the uniform field case are not observed in the sheared field case. Dynamo action is less prominent and the conversion of plasma flow energy into the other forms of energy is also smaller in the sheared field case than in the uniform field case. Momentum transport is mostly due to the hydrodynamic stress in the sheared field case, while the electromagnetic stress is dominant in the uniform field case. The long term evolutions are also markedly different in the two cases. In the uniform field geometry, the magnetic field lines twisted due to the Kelvin Helmholtz instability become reconnected and flattened so that they resume the straight field line structure which resembles the initial field geometry. The magnetic field, however, is not uniform with smaller intensity in the central region where the pressure balance is partially maintained by the enhanced thermal pressure. In the initially sheared magnetic field geometry, magnetic reconnection continues to operate until the end of the simulation and the conversion of the flow energy into the thermal energy is still seen. 相似文献
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Ikkoh Funaki Hidenori Kojima Hiroshi Yamakawa Yoshinori Nakayama Yukio Shimizu 《Astrophysics and Space Science》2007,307(1-3):63-68
To propel a spacecraft in the direction leaving the Sun, a magnetic sail (MagSail) blocks the hypersonic solar wind plasma
flow by an artificial magnetic field. In order to simulate the interaction between the solar wind and the artificially deployed
magnetic field produced around a magnetic sail spacecraft, a laboratory simulator was designed and constructed inside a space
chamber. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet is operated in a quasisteady mode of 0.8 ms duration.
It can generate a simulated solar wind that is a high-speed (above 20 km/s), high-density (1018 m−3) hydrogen plasma plume of ∼0.7 m in diameter. A small coil (2 cm in diameter), which is to simulate a magnetic sail spacecraft
and can obtain 1.9-T magnetic field strength at its center, was immersed inside the simulated solar wind. Using these devices,
the formation of a magnetic cavity (∼8 cm in radius) was observed around the coil, which indicates successful simulation of
the plasma flow of a MagSail in the laboratory. 相似文献
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Mars Express (MEX) does not carry its own magnetometer which complicates interpretation of ASPERA-3/MEX ion measurements. The direction of the interplanetary magnetic field (IMF) is especially important because it, among other things, determines the direction of the convective electric field and orientation of the cross tail current sheet and tail lobes. In this paper we present a case study to show the properties of the magnetic field near Mars in a quasi-neutral hybrid (QNH) model at the orbits where the Mars Global Surveyor (MGS) has made measurements, present a method to derive the IMF clock angle by comparing fields in a hybrid model and the direction of the magnetic field measured by MGS by deriving the IMF clock angle. We also use H+ ring velocity distribution observations upstream of the bow shock measured by the IMA/ASPERA-3 instrument on board MEX spacecraft. These observations are used to indirectly provide the orientation of the IMF. We use a QNH model (HYB-Mars) where ions are modeled as particles while electrons form a mass-less charge neutralizing fluid. We found that the direct MGS and non-direct IMA observations of the orientation magnetic field vectors in non-crustal magnetic field regions are consistent with the global magnetic field draping pattern predicted by the global model. 相似文献