The design of pion and muon channels
Date
1972
Authors
Al-Qazzaz, Nadhim
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Abstract
Various concepts for the transportation of pions and muons from production targets external to the TRIUMF accelerator have been studied. A dual purpose magnetic channel capable of providing a pion beam and a muon beam has been designed.
Phase One of the system consists of five quadrupoles and two bending magnets, and forms the pion collection section of the muon channel. It a1so serves as a stopped pion channel. The maximum solid angle of acceptance of this channel is 26 msr and the range of accepted momenta extends 17.5% on each side of the central momentum. For a 100 μA proton beam incident on a 10 cm long beryllium target, the calculated maximum stopping density of pions in an area of 25 cm x 25 cm is 1 x 108 n-(sec·g/cm2)-1 when the channel is operated at a central momentum of 100 MeV/c. A maximum muon stopping density of 7 x 106 μ-(sec·g/cm2)-1 can be obtained if the pions are separated by range absorption. Better muon beam purity is obtained by tuning the second half of the channel to 90 MeV/c to collect muons from the decay of pions in the backward direction
when the first half is set at 160 MeV/c. In this case, a maximum muon stopping density of 1 x 106 μ-(sec·g/cm2)-1 can be obtained. If a bending magnet is placed after the Phase One system to separate the muons and the pions by momentum analysis, a calculated maximum muon stopping density of 2 x 106 μ-(sec·g/cm2)-1 can be obtained when the magnet is tuned to 85 MeV/c and the channel is set at 160 MeV/c.
Phase Two of the design consists of a long straight alternating gradient section and an analyzing section. The straight section provides an extra 5.5 meter length for pion decay. When the central momentum of the pion collection system is 160 MeV/c and the straight section is tuned to optimize the number of mouns from the backward decay of pions, the calculated maximum muon stopping density in a 25 cm x 25 cm area is 1 x 107 μ-(sec·g/cm2)-1. The analyzing section consists of a 90° bending magnet and a quadrupole triplet. With the pion collection system and the straight section set as described above and the analyzing section tuned to 82 HeV/c, a calculated maximum stopping density is 3.2 x 106 μ-(sec·g/cm2)-1 in a 25 cm x 25 cm area and 1.1 x 106 μ-(sec·g/cm2)-1 in a 10 cm x 10 cm area. An average muon polarization of between 70% and 90% may be obtained. The yields of TI+ and μ+ are about three times larger than the TI- and μ- yields.
The accuracy of the calculation procedures was checked by comparing calculated and measured values for a pion channel, designed and set up at the Lawrence Laboratory at Berkeley. The two sets of values were found in agreement to within experimental error.