RECENT IMPROVEMENTS IN LUMIN&TY AT PEP+

IEEE Transactions on Nuclear Science, Vol. NS-30, No. 4. August 1983 RECENT IMPROVEMENTS IN LUMIN&TY AT PEP+ R. Helm, M. Allen, A. Chao, M. Donald, S. Kheifets, T. Martin, R. Miller, P. Morton, 3. Paterson, J Rees L. Rivkin, JY Seeman, H. Shoaee, J. Spencer, H. Wiedemann, P. Wilson, B. Richter P Stanford Linear Accelerator Center Stanford University, Stanford, California 94305 Summary Table II. Performance and limiting parametersat 14.5 GeV. We will describe improvements which have led to new records for peak and average luminosity at PEP. Compar- ison of recent results with several earlier lattice and optical modifications shows rather good correlation with the predictions of a beam-beam simulation program. I rnax W/beam) L,,(1030cm-2s-1) L,,,W-l/day) typical maximum PEP1 21 7.5 PEP2b -- 16.7 10 Introduction The PEP lattice has been modified from its original design (PEPL) by relocation of the final focus quadru- poles nearer to the interaction points. The purpose of this change was to allow operation with lower beta functions at the IPs, thereby increasing the luminositv. For a given chromatic aberration the value of 8* (the ii denotes value at the IP) scales approximately directly the distance of the final focus l&s from the IP, and the maximum luminosity is expected to vary as the in- verse of B". At PETRA and CESR the lattices were modi- fied for lower B*s and the expected luminosity improve- ments seem to have'been observed.lY2 Eymax(mm-mr) *"XmaX Av ymax 220 300 .0098 .031 .031 23 24.8 16 32.3 -- 1000 -- 1534 .0105 .0052 .033 .050 .024 .046 At PEP the changes were made in two stages. First (PEP2), in the summer df 1981 the nearest, vertically focusing quadrupole (Ql) was moved from its original distance of 11 m to 7.35 m from the IP, which is about the minimum required to accomodate the largest detectors A current-limiting instability in PEP2 required use of a different focusing configuration. To avoid this problem the next, horizontally focusing quadrupole (Q2) was moved in the summer of 1982 from the original 15.2 m to 12.24 m (PEP3). Figures 1-4 show the lattice changes and typical beta functions in the insertion region. Table I lists optical parameters for several configura- tions. Operating experience in the original lattice and the two modifications and comparison with a beam-beam simulation study are summarized below.