椭圆中子导管光学像差的校正
Correction of Optical Aberrations in Elliptic Neutron Guides
摘要：
现代非线性弹道中子导管在中子束输送和仪器中是一个有吸引力的概念，因为它们提供了比直的或线性锥形导管更高的性能。然而，像其他弹道几何形状，他们有可能创造显着的非平凡的仪器分辨率功能。我们解决的最突出的光学像差，即彗差的来源，我们表明，对于扩展源的离轴射线具有不同的焦距从轴上的射线，导致在引导系统中的多次反射。我们说明了慧差、有限尺寸的源和具有非完美反射率的镜子之间的相互作用如何共同产生中子束发散的不均匀分布，这是复杂分辨率函数的来源。为了解决这些问题，我们提出了一种混合椭圆-抛物波导几何形状。使用这种新的中子导管形状，可以调节中子束并去除几乎所有的像差，同时提供与标准椭圆形中子导管相同的束流性能。我们强调了积极的影响，这种新的形状可以带来一些中子散射仪器类型。
英文摘要：
Modern, nonlinear ballistic neutron guides are an attractive concept in neutron beam delivery and instrumentation, because they offer increased performance over straight or linearly tapered guides. However, like other ballistic geometries they have the potential to create significantly non-trivial instrumental resolution functions. We address the source of the most prominent optical aberration, namely coma, and we show that for extended sources the off-axis rays have a different focal length from on-axis rays, leading to multiple reflections in the guide system. We illustrate how the interplay between coma, sources of finite size, and mirrors with non-perfect reflectivity can therefore conspire to produce uneven distributions in the neutron beam divergence, the source of complicated resolution functions. To solve these problems, we propose a hybrid elliptic-parabolic guide geometry. Using this new kind of neutron guide shape, it is possible to condition the neutron beam and remove almost all of the aberrations, whilst providing the same performance in beam current as a standard elliptic neutron guide. We highlight the positive implications for a number of neutron scattering instrument types that this new shape can bring.
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