Beam lines group at PSI

µE4 beam line

The µE4 is optimized for an intense polarized muon beam in the momentum range between 30 and 100 MeV/c. Its layout essentially duplicates that of µE1 :

a high acceptance pion section
a superconducting solenoid
an extraction section

The beam line is attached to the target station TE at an angle of 90°, and the system has been adapted to the 6 cm length of the carbon production target. Matching the lower pion energies available, the superconducting solenoid is only 5 m long. The extraction system can be operated in two different modes :

Mode A is achromatic yielding higher muon fluxes

Mode B is chromatic (or analyzing) yielding four times smaller range widths at a corresponding cost of intensity

The following table lists the main characteristics of the extraction section.The layout of the experimental area and of the magnetic components are shown in Fig 1 and Fig 2 . In Fig 3 the measured negative muon fluxes and ranges as a function of momentum are plotted. The flux for positive muons is higher by a factor of four.

Table 1 : Characteristics of the µE4 beam line

   Mode                                        A                  B

   Momentum acceptance (FWHM)                 15%                 3%
   Beam spot at solenoid end (mm FWHM)               50 horiz.
                                                     35 vert.
   Beam divergence at solenoid end                  100 horiz.
   [mrad FWHM]                                      300 vert.
   CH2 range width at 88.5 MeV/c [g/cm²]      2.0                 0.55
   CH2 range width at 50.0 MeV/c [g/cm²]      0.3                 0.10
   Beam spot size at target (mm FWHM)                 60 horiz.
                                                      40 vert.
   Mean muon polarization [%]                         75

The muon channel µE4 has the following advantages over the µE2 channel :

It is designed for experiments requiring low momentum and/or small range widths, as seen in Fig 4 . It is possible to select even lower muon momenta than 50 MeV/c and to obtain correspondingly smaller widths by degrading the pions in front of the channel.

Low neutron background due to the use of a 90° pion production angle. Since the muon area µE4 is located at backward angles with respect to the target TE and the beam dump, very few high energy ( > 100 MeV/c) neutrons rach the area from these sources(1/1000 neutrons 1/mA s cm²). The main source of fast neutrons in the energy range from 1 to 100 MeV/c is therefore the pion dump after the last bending magnet, which is well shielded. A second source of neutrons (in case of negative muons operation) is the slit system where the halo muons are dumped.

There is a manual in pdf format with more details. Conversion from DAC values to field values and vice versa, can be done using the TUNE and ITUNE programme .

The coordinator for this beam line is F. Foroughi .

F. Foroughi .