Neutron resonance spin echo with longitudinal DC fields.
Neutron resonance spin echo with longitudinal DC fields.
复制标题
具有纵向直流场的中子共振自旋回波。
DOI：
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发表时间：
2016
影响因子：
1.6
通讯作者：
W. Häussler
中科院分区：
文献类型：
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作者：
M. Krautloher;J. Kindervater;T. Keller;W. Häussler
本文报道了一台中子共振自旋回波(NRSE)仪器的设计、结构和性能，该仪器采用射频(RF)自旋触发器，结合了射频场和直流场，后者定向平行(纵向)于中子传播方向(纵向NRSE(LNRSE))。纵向结构的优点是有效磁路积分的内在均匀性。在RF线圈的中心，通过中子自旋的π翻转来反转自旋进动相位的符号，从而抵消了在RF触发器边界处的不均匀自旋进动。像常规的自旋回波仪器(中子自旋回波(NSE))一样，菲涅耳线圈或毕达哥拉斯线圈可以减少残留的不均匀性。由于B0线圈具有良好的本征均匀性，校正线圈所需的电流密度至少比传统的NSE低三倍。由于校正线圈的精度和电流密度是NSE和LNRSE分辨率的限制因素，后者具有超越现有NSE仪器能量分辨率的内在潜力。我们的原型LNRSE光谱仪是在德国加兴MLZ的共振自旋回波(REEDA)光束线上实现的。直流场由B0线圈产生，基于具有有源屏蔽的阻性分裂对螺线管，用于沿光束路径的低杂散场。一对2米距离的射频触发器产生∼0.5TM的场积分。LNRSE技术是未来准弹性激发的高分辨率光谱的替代技术。此外，它还结合了Mieze技术，该技术允许实现自旋去极化样品和样品环境的自旋回波分辨率。在这里，我们给出了线圈几何形状的数值优化结果和样机的第一批数据。
We report on the design, construction, and performance of a neutron resonance spin echo (NRSE) instrument employing radio frequency (RF) spin flippers combining RF fields with DC fields, the latter oriented parallel (longitudinal) to the neutron propagation direction (longitudinal NRSE (LNRSE)). The advantage of the longitudinal configuration is the inherent homogeneity of the effective magnetic path integrals. In the center of the RF coils, the sign of the spin precession phase is inverted by a π flip of the neutron spins, such that non-uniform spin precession at the boundaries of the RF flippers is canceled. The residual inhomogeneity can be reduced by Fresnel- or Pythagoras-coils as in the case of conventional spin echo instruments (neutron spin echo (NSE)). Due to the good intrinsic homogeneity of the B0 coils, the current densities required for the correction coils are at least a factor of three less than in conventional NSE. As the precision and the current density of the correction coils are the limiting factors for the resolution of both NSE and LNRSE, the latter has the intrinsic potential to surpass the energy resolution of present NSE instruments. Our prototype LNRSE spectrometer described here was implemented at the resonance spin echo for diverse applications (RESEDA) beamline at the MLZ in Garching, Germany. The DC fields are generated by B0 coils, based on resistive split-pair solenoids with an active shielding for low stray fields along the beam path. One pair of RF flippers at a distance of 2 m generates a field integral of ∼0.5 Tm. The LNRSE technique is a future alternative for high-resolution spectroscopy of quasi-elastic excitations. In addition, it also incorporates the MIEZE technique, which allows to achieve spin echo resolution for spin depolarizing samples and sample environments. Here we present the results of numerical optimization of the coil geometry and first data from the prototype instrument.