SLC positron source-simulation and performance

The main goal of the extensive program of simulation and experiment for the SLC positron system was to establish benchmarks at locations where beam characteristics could be measured well, and to use ray tracing to judge and predict the quality of the positron beam delivered to the SDR (South Damping Ring), to make sure that the beam was within the measured acceptance of the SDR. Performance of the source was found to be in good general agreement with computer simulations with S-band acceleration and, where not, the simulations led to identification of problems, particularly the underestimated impact of linac misalignments due to the 1989 Loma Prieta earthquake. It is suggested that the earthquake resulted in a loss of approximately 20% positron yield during the following year, because the impact of the known misalignment was underestimated. At present the quadrupoles in sector 1 are aligned no better than 0.2 mm RMS. It is suggested that aligning sector 1 to the design value of 0.1 mm should increase the number of positrons at the damping ring by 7%.<>