上海光源储存环主支撑减振研究

 上海光源是一台在建的第三代同步辐射光源,对束流轨道稳定性要求很高。由磁铁和支架组成的支撑组件的机械稳定性是影响束流轨道稳定性的重要因素。对主支撑组件样机的测试结果表明,其最低共振频率处放大倍数为50左右,超过要求5倍。因此,需要研究相应的减振措施。利用阻尼减振原理设计了一种约束阻尼结构。在样机上的测试结果表明,安装该装置后,支撑组件的共振放大倍数最大可以降低91.8%,对应的功率谱密度的峰值可以降低25 dB。因此,该装置可以用来增加支撑的稳定性。     

EPICS在加速器控制系统中的应用

 介绍了当前国内外大型加速器实验室采用的主流控制系统软件开发工具EPICS的总体结构和特点,主要介绍了ASYN结构和特点,以及对使用ASYN软件包建立磁铁电源串口设备支持模块进行的研究,并将其应用于中国工程物理研究院驱动自由电子激光的30 MeV直线加速器磁铁电源控制系统中。同时还具体介绍了磁铁电源控制系统的结构以及系统软件设计,为直线加速器控制系统的建设做好准备工作。使用EPICS开发工具建立的加速器控制系统可以满足实验要求的高可靠性和高稳定性,从而为自由电子激光实验提供高品质束流。     

范德瓦尔斯磁性材料CrOCl变磁性相变的磁力显微镜研究

近年来,二维范德瓦尔斯磁性材料因为在自旋电子学的应用前景而吸引了广泛的关注.CrOCl是一种范德瓦尔斯磁性材料,理论预言其单层具有高达160 K的居里温度,因此吸引了广泛的关注。为了更好的理解这一材料的磁性,我们利用磁力显微镜研究了CrOCl变磁性相变中磁畴结构随磁场的变化。实验发现,在2K下CrOCl样品表面出现随磁场变化的方格条纹,给出了变磁性相比中反铁磁相和铁磁相竞争的图样,并通过二维快速傅里叶变换证实了CrOCl磁性的各向异性。我们的结果为后续研究CrOCl薄层的磁性提供了参考依据。     

A constant gradient unilateral magnet for near-surface MRI profiling

The design and construction of a unilateral NMR (UMR) magnet assembly for near-surface 1D profiling is presented. The arrangement consists of a single permanent magnet topped with a shaped iron pole cap. The analytically determined profile of the pole cap shapes the field over the magnet, giving a constant gradient of 31 G/cm over a 8mm depth at a 1H frequency of 4.26 MHz in a spot approximately 5 mm wide. The moderate gradient allows 1D profiling of planar samples with a frequency encoded spin-echo experiment. The curvature of the magnetic field limits the available resolution to 100's of microm. The device is suitable for profiling planar samples in which a coarse resolution but large spatial extent is desired.     

A novel technique for imaging with inhomogeneous fields

We introduce a simple, efficient, low-SAR method for magnetic resonance imaging in the presence of a static field with a permanent, and possibly large gradient. The technique, which is called slant-slice imaging is essentially a spin-echo imaging sequence except that the imaging slice is oriented such that the static field gradient can be used in conjunction with applied gradients during readout. Data are collected for 2D slices. Unlike single point imaging techniques, entire lines of k-space are acquired with each readout. The slant-slice pulse sequence is used to obtain high quality images, using a clinical scanner to simulate a static field with a large permanent gradient. The effects of the inhomogeneity are quantified by two parameters nu and q, which are useful for assessing the utility of a magnet design for 3D-MR imaging.