Electron Positron Factories - eScholarship

LBL--30858 DE91 016981 ELECTRON POSITRON FACTORIES t Michael S. Zisman, S. Chattopadhyay, Alper A. Garren, Glen Lambertson Lawrence Berkeley Laboratory, Berkeley, CA 94720 Elliott Bloom, William J. Corbett, Massimo Cornacchia, Jonathan M. Dorfan Stanford Linear Accelerator Center, Stanford, CA 94309 William A. Barletta Lawrence Livermore National Laboratory, Livermore, CA 94550 Dip-ter Mohl CERN, Geneva 23, Switzerland Claudio Pellegrini University of California, L.os Angeles, CA 90024 navid Rice Cornell University, Ithaca, NY 14853 Matthew Sands University of California, Santa Cruz, CA 95064 1. Introduction GENERAL In the design of an e+ e- circular collider to serve as a B-factory, a ¢-factory, or a r-charm- factory, the beam energies are defined by the res- onant nature of the interaction cross section. The challenge in the accelerator design, then, is to push on the luminosity frontier rather than the energy frontier. Thus, it is issues related to the high beam intensities and the large number of col- liding bunches that are paramount. The goal of all these factories is to achieve lu- minosity values approximately two orders of mag- nitude beyond those of existing colliders in the ap- propriate energy range. In all operating e+e-mach- ines, however, there is one characteristic param- eter that has proven resistant to large improve- ments from particular design choices-the beam- beam space charge tune shift parameter, This parameter-in all operating e+e-colliders and in all energy ranges-lies between about 0.02 and 0.06. It does not seem reasonable, then, to base a design on a value for that is well beyond the range that has been seen in experiments over e. e many years and that has resulted from numerous detailed and sophisticated simulation codes. With this constraint in mind. the design op- tions invariably proceed along two paths, as illus- trated in Fig.!. First, the lattice design is pushed tc produce very low values of f3;. This cheice forces a concomitant reduction in the bunch length to reach the operating regime where {7 L :$ /3;, along with a substantial amount of RF hardware to produce the short bunch. Second, achieving high luminosity without a greatly increased value forces the design to one with many bunches (hun- dreds, or even thousailds). To avoid numerous parasitic bunc!! crossings, and because of the large circulating currents, designs for B- and r-charm- factories have uniformly adopted a two-ring ap- proach. In a ¢-factory, such an approach is not mandatory. Subsequent branches in the design logic are indicated in Fig. 1. The performance criterion of any flavor fac- tory is usable integrated luminosity per year. A good duty cycle is required in addition to high peak luminosity. Defining a duty cycle D == CIC over on. vear of calendar time, present e+ e- collid- ers oper~te at D - 0.25[1,2]. For a B-factory with C = 3 X 10 33 , D must be close to 0.4 to ac- e Work supported by the Department of Energy contracts DE-AC03-76SF00515, DE-FG03-90ER40565, DE- AC03·76SF00098 and W-7405-ENG-48, and the National Science Foundation. MASTER