πE5 Beam Line

The πE5 beam line is a low energy (10-120 MeV/c) pion and muon beam line, viewing the thick target at 175° with respect to the primary proton beam. The main properties of the beam line are given in the following table. The beam line and a layout of the experimental area are shown in Fig 1 and Fig 2 respectively.
Length 10.4 m
Solide angle 150 msr
Momentum acceptance (FWHM) 10 %
Momentum resolution (FWHM) 2 %
Spot size (FWHM) 15 mm horizontal
  20 mm vertical
Angular divergence (FWHM) 450 mrad horizontal
  120 mrad vertical
The second bending magnet AST is designed in a way that the beam can serve alternatively two experiments at the location U and Z as indicated in the layout, within a short switching time.

In the middle of the beam line, where the momentum restricting slit system is located, the aberrations are rather large and therefore the momentum resolution is poor (2% FWHM). The situation is better at the final focus since the beam line is built up symmetrically causing some aberrations to vanish at the end.

There are three sets of horizontal and one set of vertical slits, which define the momentum and/or the acceptance in the two versions of optics which correspond to the two positions for experiments at locations U and Z.

Plots of the rates and phase space at the focus just behind the seocnd bending manet AST are shown if Fig 3 and Fig 4 respectively.

Due to the large opening of the vacuum chamber and the relatively small bending radii, there is a high neutron background in the region of the second bending magnet. Estimated fluxes are : 150 neutrons mA-1 s-1 cm-2 at energies larger than 120 MeV, and low energetic neutrons, which produce a radiation level of 50 mS mA-1 h-1.