ILL的PF1B仪器用固体中子极化器的研制
A project of advanced solid-state neutron polarizer for PF1B instrument at ILL
摘要：
在超镜（SM）偏振器中，固态器件具有许多优点。最相关的是与气隙偏振器相比小5-10倍的长度，允许施加更强的磁场。一个好的SM偏振器的一个重要条件是匹配的衬底SLD（散射长度密度）与SM涂层SLD的自旋下降中子。对于传统的Si衬底上的Fe/Si SM，当中子从衬底到达SM时，该SLD阶跃为正，这导致在小Q下偏振器性能的显著损失。相反，我们使用单晶蓝宝石/石英基板。后者在与Fe的界面处显示出负的自旋下降中子SLD阶跃，因此避免了小Q时的全反射区。为了优化偏振器的性能，我们制定了蓝宝石V型弯曲器的概念，进行光线跟踪模拟的蓝宝石V型弯曲器，比较结果与传统的C型弯曲器在Si上，和实验研究不同基板的V型弯曲器原型。我们的结果表明，基板材料的选择，偏振器的几何形状和磁化场的强度和质量有显着的影响。特别地，我们比较了偏振器对于$50 mT$和$300 mT$的施加磁场强度的性能。只有大的场强提供了一个很好的协议之间的模拟和测量的偏振值。对于双碰撞组态，在$0.3-1.2 nm$的中子波段获得了记录的极化$>0.999$，在$2 nm$只有$1\%$降低。在没有任何准直的情况下，发现在整个出射捕获光谱$0.997$上平均的偏振等于先前仅使用“交叉”（X-SM）几何中的双偏振器获得的值。这些结果被应用在一个全尺寸的偏振器的PF 1B仪器。
英文摘要：
Among Super-Mirror (SM) polarizers, solid-state devices have many advantages. The most relevant is 5-10 times smaller length compared to air-gap polarizers allowing to apply stronger magnetic fields. An important condition for a good SM polarizer is the matching of the substrate SLD (Scattering Length Density) with the SM coating SLD for spin-down neutrons. For traditional Fe/Si SM on Si substrate, this SLD step is positive when a neutron goes from the substrate to the SM, which leads to a significant loss of the polarizer performance at small Q. Instead, we use single-crystal Sapphire/Quartz substrates. The latter show a negative SLD step for spin-down neutrons at the interface with Fe and, therefore, avoid the total reflection regime at small Q. To optimize the polarizer performance, we formulate the concept of Sapphire V-bender, perform ray-tracing simulations of Sapphire V-bender, compare results with those for traditional C-bender on Si, and study experimentally V-bender prototypes with different substrates. Our results show that the choice of substrate material, polarizer geometry and the strength and quality of magnetizing field have dramatic effect. In particular, we compare the performance of polarizer for the applied magnetic field strength of $50 mT$ and $300 mT$. Only the large field strength provides an excellent agreement between the simulated and measured polarization values. For the double-collision configuration, a record polarization $>0.999$ was obtained in the neutron wavelength band of $0.3-1.2 nm$ with only $1\%$ decrease at $2 nm$. Without any collimation, the polarization averaged over the full outgoing capture spectrum, $0.997$, was found to be equal to the value obtained previously only using a double polarizer in the "crossed" (X-SM) geometry. These results are applied in a full-scale polarizer for the PF1B instrument.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
