PSI低能μ子装置束斑优化的分段锥形电透镜：Geant4模拟分析
A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis
摘要：
PSI的低能μ子设施提供了几乎完全极化的正μ子，其能量在keV范围内可调，以在薄膜、异质结构和近表面区域上进行μ子自旋旋转（LE-muSR）实验，具有纳米深度分辨率。低能μ子束通过静电透镜聚焦并传输到样品。为了在样品位置实现最小的束斑尺寸，并使束能够在水平和垂直方向上转向，在样品位置附近安装了一个特殊的静电装置。它由一个接地电位的圆柱体和四个圆锥形电极组成，这些电极可以在不同的电势下工作。在LE-muSR实验中，可以沿束方向在样品处施加电场以将μ子加速/减速到不同的能量（0.5-30 keV）。此外，水平或垂直磁场可以叠加用于横向或纵向场muSR实验。在这些额外的电场和磁场的存在下，锥形透镜的聚焦特性进行了研究和优化的Geant 4模拟。一些实验测试也进行了，并表明模拟很好地描述了实验装置。
英文摘要：
The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the keV range to carry out muon spin rotation (LE-muSR) experiments with nanometer depth resolution on thin films, heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes, which can be operated at different electric potential. In LE-muSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies (0.5-30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field muSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.
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