Operation of PEP in a low emittance mode

PEP has been used as a source of synchrotron radiation with an undulator beam line operating parasitically during particle physics runs at 14.5 GeV beam energy. The possibilities of using PEP in a dedicated mode for synchrotron radiation have been considered. Since a lower beam energy is preferred in this case, PEP has been successfully operated at 8 GeV where the uncoupled beam emittance is 27 nm rad. It is of interest to reduce this emittance further with a different optics having stronger horizontal focussing. This has been done by increasing the horizontal betatron phase advance per cell from 560 to 1000 resulting in an emittance of about 9 nm rad. To keep the strength of the sextupoles and their effect on the dynamic acceptance of the ring small, the natural chromaticity was reduced by having parallel focussing in the intersection points instead of the usual low-beta optics. The dynamic acceptance of such a configuration has been tested by particle tracking and found to be larger than the physical aperture. This optics does not require new hardware but was implemented by changing the powering of the different optical elements. In a brief run at 8 GeV a beam was successfully injected and accumulated. The horizontal and vertical emittances were measured using the photon beam of the 58 m long undulator beam line and found to be 12.1 and 1.2 nm rad. This is close to the expected value of 9.9 nm rad for the sum of the two. The beam life time was over 30 hours at low currents. Different methods of reducing this emittance even further are investigated