VEPP-2000 Operation with Round Beams in the Energy Range from 1 to 2 GeV D. Berkaev a , A. Kirpotin a , I. Koop a , A. Lysenko a , I. Nesterenko a , A. Otboyev a , E. Perevedentsev a , Yu. Rogovsky a , A. Romanov a , P. Shatunov a , Yu. Shatunov a , D. Shwartz a , A. Skrinsky a , I. Zemlyansky a a Budker Institute of Nuclear Physics of Siberian Branch Russian Academy of Sciences, Novosibirsk, Russia Abstract The idea of round-beam collision was proposed more than twenty years ago for the Novosibirsk Phi-factory de- sign [1]. It requires equal emittances, equal small fractional tunes, equal beta functions at the IP, no betatron coupling in the collider arcs. Such an approach results in conservation of the longitudinal component of angular momentum. As a consequence, it yields an enhancement of dynamical stability, even with nonlinear effects from the beam-beam force taken into account. The Round Beam Concept (RBC) was realized at the electron-positron collider VEPP-2000 and successfully tested at the energy of 510 MeV [2]. Despite the low energy, a high single-bunch luminosity of 10 31 cm -2 s -1 was achieved together with a maximum tune shift as high as 0.1. At present the work is in progress to increase the energy of the collider to explore the range between 500 MeV and 1 GeV in collision. 1. Collider overview The VEPP-2000 electron-positron collider has to op- erate in the beam energy range 0.2–1 GeV. It was con- structed at the place of its predecessor VEPP-2M, us- ing the existing beam production chain of accelerators: ILU – a pulsed RF cavity with a voltage of 2.5 MeV, a 250 MeV synchrotron B-3M and a booster storage ring BEP with the maximum beam energy of 825 MeV (see Fig. 1). VEPP-2000 lattice has a two-fold symme- try with two experimental straight sections 3 m long, where the Cryogenic Magnetic Detector and Spherical Neutral Detector are located. Two other long straights (2.5 m) are designed for injection of beams and RF cav- ity, and 4 short technical straights accomodate triplets of quadrupole magnets (maximum gradient 50 T/m). To avoid dispersion inside the detectors, an RF cavity and injection straights, a couple of dipoles together with the triplet in between constitute 4 achromats. Chromaticity corrections are performed by two families of sextupole magnets located in the technical straight section, where the dispersion is high. Design parameters of the collider are given in Table 1. Closed orbit steering and gradient corrections are done with 1–2% coils placed in the dipole and Parameter Value Circumference, Π 24.39 m Betatron functions at IP, β ∗ x,z 10 cm Betatron tunes, ν x,z 4.1, 2.1 Beam emittance, ǫ 1.4 × 10 -7 m rad Momentum compaction, α 0.036 Synchrotron tune, ν s 0.0035 Energy spread, σ ΔE/E 6.4 × 10 -4 Beam-beam parameters, ξ 0.075 Luminosity, L 10 32 cm -2 s -1 Table 1: VEPP-2000 main parameters (at E = 1 GeV). quadrupole magnets. An accelerating HOM-damping RF cavity operates at the 14-th harmonic of the revolution frequency (172.0 MHz) [6]. It provides a bunch length of about 3 cm at the top energy and stability of design bunch cur- rent of 200 mA. Beam diagnostic is based on 16 optical CCD cam- eras, that register the synchrotron light from either end of the bending magnets and give the full informa- tion about beam positions, intensities and profiles (see Fig. 2). In addition to optical BPMs, there are also 4 Available online at www.sciencedirect.com Nuclear Physics B (Proc. Suppl.) 225–227 (2012) 303–308 0920-5632/$ – see front matter © 2012 Elsevier B.V. All rights reserved. www.elsevier.com/locate/npbps doi:10.1016/j.nuclphysbps.2012.02.063