Nonlinear effects in the SLC e+ transport line

The target area of the SLC positron system, 2 km down the linac, is connected back to the front end of the machine by 2 km-long transport line, consisting of 75 FODO cells, with a quadrupole aperture of 10 cm. The beam in the return line experiences a loss larger than predicted. Taking into account the relatively high dodecapole component in the FODO lattice quadrupoles of 2.5% of the quadrupole component at a radius of 4.65 cm, it is found through particle tracking that nonlinear resonances occur for certain values of the phase advance per FODO cell, particularly at 90 degrees , the standard value previously used. These resonances lead to particle loss in the outer layers of phase space due to the particles with a large amplitude being more affected by the dodecapole moment.<
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