# Nuclear Science and Techniques

《核技术》(英文版) ISSN 1001-8042 CN 31-1559/TL     2019 Impact factor 1.556

Nuclear Science and Techniques ›› 2017, Vol. 28 ›› Issue (3): 29

• NUCLEAR PHYSICS AND INTERDISCIPLINARY RESEARCH •

### A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

Ran Xiao 1,2,3  Elvezio Morenzoni 3  Zaher Salman 3  Bang-Jiao Ye 1,2  Thomas Prokscha 3

1. 1 State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei 230026, China
2 Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
3 Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland
• Contact: Ran Xiao; Thomas Prokscha E-mail:xran@mail.ustc.edu.cn; thomas.prokscha@psi.ch
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Ran Xiao, Elvezio Morenzoni, Zaher Salman, Bang-Jiao Ye, Thomas Prokscha. A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis.Nuclear Science and Techniques, 2017, 28(3): 29
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Abstract:

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-lSR) 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 LElSR 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 lSR 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.