Beam Line

The beam line supplies high intensity pion and muon beams with momenta ranging from 10 to 500 MeV/c. Figure 2.1 shows the layout of the beam line [17].

  
Figure 2.1: Magnetic elements of beam line.

Two modes of operation are available [17]:

• Mode A provides high flux with low momentum resolution. Its momentum is limited by the focusing strength of the first quadrupoles to values lower than 280 MeV/c.
• Mode B is a low acceptance, high momentum resolution version up to momenta of 500 MeV/c.

The defining characteristics of the beam line are summarized in Table 2.1.

  
Table 2.1: Characteristics of the beam line in Mode A (high flux) and Mode B (high momentum resolution).

In the 1997 data run, the beam line was tuned in Mode B for 116 MeV/c negative pions. This tune is shown in Figure 2.2 as the output of the TRANSPORT [20] program calculation. In the figure, the top solid line represents the beam envelope in the horizontal (x) direction, and the bottom solid line the beam envelope in the vertical (y) direction. The arrows represent collimators and slits in the beam path, and the dotted line is the momentum dispersion measured in cm/% in the x direction.

  
Figure: The beam tune for the 1997 data run. The top part of the graph represents the x direction, and the bottom the y direction. The arrows indicate collimation, and the dotted line is the beam momentum dispersion, measured in cm/%. These calculations were made with the TRANSPORT program.