Krautloher Maximilian, Kindervater Jonas, Keller Thomas, Häußler Wolfgang
Physik-Department, Technische Universität München, D-85748 Garching, Germany.
Max Planck Institute For Solid State Research, 70569 Stuttgart, Germany.
Rev Sci Instrum. 2016 Dec;87(12):125110. doi: 10.1063/1.4972395.
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 B 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 B 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.
我们报告了一种采用射频（RF）自旋翻转器的中子共振自旋回波（NRSE）仪器的设计、建造和性能，该射频自旋翻转器将射频场与直流场相结合，直流场与中子传播方向平行（纵向）（纵向NRSE（LNRSE））。纵向配置的优点是有效磁路积分具有固有的均匀性。在射频线圈的中心，中子自旋的π翻转会使自旋进动相位的符号反转，从而消除射频翻转器边界处的非均匀自旋进动。与传统自旋回波仪器（中子自旋回波（NSE））的情况一样，可以通过菲涅耳线圈或毕达哥拉斯线圈来降低残余的不均匀性。由于B线圈具有良好的固有均匀性，校正线圈所需的电流密度比传统NSE至少小三分之一。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，因此LNRSE具有超越现有NSE仪器能量分辨率的内在潜力。我们在此描述的LNRSE光谱仪原型是在德国加兴的MLZ的共振自旋回波用于多种应用（RESEDA）束线中实现的。直流场由B线圈产生，基于具有有源屏蔽的电阻式分裂对螺线管，以降低沿束线的杂散场。一对相距2 m的射频翻转器产生的场积分约为0.5 Tm。LNRSE技术是准弹性激发高分辨率光谱学的未来替代方案。此外，它还结合了MIEZE技术，该技术可实现对自旋去极化样品和样品环境的自旋回波分辨率。在此，我们展示了线圈几何形状的数值优化结果以及来自原型仪器的首批数据。
