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The swinger consists of two large dipole magnets, labelled entrance magnet and swinger magnet in figure gif. In a time-of-flight experiment of the sort that was carried out here the detector is necessarily confined to a single point at the end of a long flight path. This means that it is not possible, or at least extremely inconvenient, to move the detector to measure observables at different scattering angles. Instead the entrance and swinger magnets bend the proton beam so that it is incident on the target from a different angle, as shown in figure gif.

Figure: Schematic view of the proton path through the beam swinger [Hua91].

This effectively changes the scattering angle and, therefore, the momentum transfer at which measurements are being made. The combination of the two magnets can swing the beam to any angle between and . Figure gif also shows that there are two flight paths away from the target; one at and one at , both of which were in use during the experiment. This allows measurements to be taken at two angles simultaneously (separated by ) out to , or a momentum transfer of . It should be noted that at any angle aside from the polarization of the incoming protons with an in-plane polarization ( or ) will be precessed by the dipole fields. This extra precession must be compensated for by the BL3 and BL5 precession solenoids.

Michael A. Lisa
Tue Apr 1 08:52:10 EST 1997