PROJECT OF A NEW ELECTRON-POSITRON COLLIDER VEPP-2000 Yu.M. Shatunov, A.V. Evstigneev, D.I. Ganyushin, P.M. Ivanov, I.A. Koop, V.S. Kuzminykh, A.P. Lysenko, N.A. Mezentsev, N.V. Mityanina, I.N. Nesterenko, A.V. Otboev, E.A. Perevedentsev, V.M. Petrov, D.B. Schwartz, P.Yu. Shatunov, A.N. Skrinsky, A.A. Valishev, V.N. Volkov, Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia Abstract The status of VEPP-2M collider is presented. Implementa- tion of Round Colliding Beams (RCB) concept in the new collider VEPP-2000 is outlined, potential advantages of RCB over the flat colliding beams are discussed. The main design parameters and features of this VEPP-2000 collider are reported. 1 STATUS OF VEPP-2M AND MOTIVATION FOR THE CONSTRUCTION OF A NEW COLLIDER Since the end of 1992 the e + e - collider VEPP-2M in Novosibirsk has been successfully running in the c.m. en- ergy range from threshold of hadron production up to 1.4 GeV. Since 1984 VEPP-2M is operating with the five poles superconducting wiggler with the maximum field B =8 T, which increases the beam emittance by a factor of ≃ 3. The integrated luminosity of about 50 pb -1 was collected with two modern detectors SND[1] and CMD-2[2] allow- ing precise measurements of most of the hadronic chan- nels of e + e - annihilation. Together with 24 pb -1 collected at VEPP-2M in the previous generation of experiments in 1974-1987, this integrated luminosity is more than one or- der of magnitude higher than about 6 pb -1 accumulated by various experimental groups in Frascati and Orsay in the c.m. energy range from 1.4 to 2 GeV. Thus, there is a seri- ous energy gap between the maximum energy attainable at VEPP-2M and 2 GeV in which existing data on e + e - anni- hilation into hadrons are rather imprecise. Accurate mea- surements of hadronic cross sections in this energy range are crucial for better understanding of many phenomena in high energy physics. A recent decision to upgrade the VEPP-2M complex by replacing the existing collider with a new one, in order to improve the luminosity and at the same time increase the maximum attainable energy up to 2 GeV, will significantly broaden the potential of experiments performed at the col- lider. Following modern trends, the new project was named VEPP-2000. 2 ROUND COLLIDING BEAMS During the last decade at BINP the concept of Round Col- liding Beams (RCB)[3] was proposed. The evident advantage of round colliding beams is that with the fixed particle density, the tune shift from the op- posite bunch becomes twice as small as the tune shift in the case of flat colliding beams. Besides, the linear beam- beam tuneshift in the round beams becomes independent of the longitudinal position in the bunch, thereby weakening the action of synchro-betatron resonances. The main feature of the RCB is rotational symmetry of the kick from the round opposite beam; complemented with the X −Z symmetry of the betatron transfer matrix be- tween the collisions, it results in conservation of particle’s angular momentum. Thus, the transverse motion becomes equivalent to a one-dimensional (1D) motion. Resulting elimination of all betatron coupling resonances is of cru- cial importance, since they are believed to cause the beam lifetime degradation and blow-up. The above arguments in favour of RCB have been checked out by the computer simulations of the beam- beam effects in RCB option[4]. The simulations have also demonstrated stability of RCB against the “flip-flop” effect, similarly to conclusions from simple flip-flop models[5]. 3 VEPP-2000 PROJECT Figure 1: The VEPP-2000 collider layout 3.1 Collider Optics Our approach to the new collider optics is based on the idea of round colliding beams [3]. The main principles of round beam mode will be satisfied by placing SC solenoids in 439 Proceedings of EPAC 2000, Vienna, Austria