Spear -present Status and Improvement Program*

Initial operating experience with the SLAC electron-positron storage ring SPEAR is described. A single-beam coherent instability, which can be suppressed either by control of the ring chromaticity or by feedback, has been observed. A second single-beam coherent instability has been observed at currents around 50 mA and is not yet understood. Current-dependent bunch lengthening and widening have been observed, and experiments indicate that these phenomena may be associated with an increase in the energy spread of the beam. A luminosity of 2 x 1030 cmm2 set-l has been achieved and two-beam interaction effects are described. Procedures to increase the luminosity to the design value of 1O32 cme2 set -1 at 2 GeV are discussed. Plans to increase the maximum beam energy of SPEAR to 4.5 GeV are described. *Work supported by the U. S. Atomic Energy Commission. **P. Morton, R. McConnell, J. Rees, B. Richter, A. Sabersky, R. Scholl, J. Voss, H. Wiedemann (visitor from DESY, Hamburg, West Germany), M. Allen, J. -E. Augustin (visitor from University of Paris, Orsay, France), A. Boyarski, W. Davies-White, N. Dean, G. Fischer, J. Haissinski (visitor from University of Paris, Orsay, France), J. L. Harris, L. Karvonen, R. R. Larsen, and M. J. Lee. (Presented at the IIIrdAll Union Conference for Scientific Problems of Charged Particles Accelerators, Moscow, October 2 4, 1972.)