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A new approach to high-current operation of the Advanced Photon Source.

It is shown that the operation of the Advanced Photon Source (APS) storage ring at 6 GeV will (1) deliver higher brilliance at x-ray energies used by a majority of users due to natural reduction in electron beam emittance at lower storage ring energy, and (2) lower the total power produced by insertion devices thus permitting stored currents up to 300 mA with minimal changes in accelerator or beamline hardware. While higher brilliance x-ray beams can be realized from the APS undulators by only increasing the stored current for the present modes of operation, this however leads to serious high heat load concerns. This report includes detailed analyses of radiation brilliance, undulator tunability, power, power density, and total and coherent flux as a function of x-ray energy from various harmonics of undulator-A, for operation at 6.0, 6.5 and 7.0 GeV with 100, 140, 200 and 300 mA currents. A discussion of a smaller period (2.7 cm) undulator's spectral performance is also presented. It is shown that the APS can be immediately operated at 6 GeV with 200-300 mA current to benefit user science in the x-ray energy range below 35 keV. This may not require any hardware change either in the storage ring or the beamlines, making this switch without any interruptions to user research programs. Finally, the suggested 6 GeV operation with 300 mA should be considered a temporary step towards higher brilliance operation. A need for re-optimization of the APS technical operations, defined by storage-ring energy, current, undulator period, and power, are also addressed in this report.