Design of a 10cms Super-b Factory *

Parameters have been studied for a high luminosity e+ecollider operating at the Upsilon 4S that would deliver a luminosity of 1 to 4 x 10/cm/s. This collider, called a Super-B Factory, would use a combination of linear collider and storage ring techniques. In this scheme an electron beam and a positron beam are stored in lowemittance damping rings similar to those designed for a Linear Collider (LC) or the next generation light source. A LC style interaction region is included in the ring to produce sub-millimeter vertical beta functions at the collision point. A large crossing angle (+/24 mrad) is used at the collision point to allow beam separation. A crab-waist scheme is used to reduce the hourglass effect and restore peak luminosity. Beam currents of 1.8 A at 4 x 7 GeV in 1251 bunches can produce a luminosity of 10/cm/s with upgrade possibilities. Such a collider would produce an integrated luminosity of about 10,000 fb (10 ab) in a running year (10 sec) at the Υ(4S) resonance. Further possibilities include having longitudinally polarized eat the IR and operating at the J/Psi and Psi’ beam energies. DESIGN STRATEGY The construction and operation of modern multi-bunch ee colliders [1,2,3] have brought about many advances in accelerator physics in the area of high currents, complex interaction regions, high beam-beam tune shifts, high power RF systems, controlled beam instabilities, rapid injection rates, and reliable uptimes (~90%). A Conceptual Design Report (CDR) [4] was issued in May 2007, with about 200 pages dedicated to the accelerator design. This report discusses site requirements, crab waist compensation, parameters optimization in order to save power, IP quadrupole design, Touschek backgrounds, spin rotator scheme, and project costs. A possible layout at Tor Vergata University near Rome is shown in Figure 1. The ring lattices have been modified to produce very small horizontal (a few nm-rad) and vertical emittances (a few pm-rad). Crab waist sextupoles near the interaction region introduce a left-right longitudinal waist position variation in each beam allowing a vertical beta function which is much smaller than the bunch lengths. *Supported by US DOE contract DE-AC02-76SF00515. [email protected] ___________________________ Figure 1: Possible SuperB location at Tor Vergata University with a ring circumference of 1800 m and an injector located adjacent to the future SPARX FEL. LUMINOSITY AND CROSSING ANGLE The luminosity L and beam-beam parameters, ξy, ξx, in an ee collider with a horizontal crossing angle are given by the expressions: where fc is the frequency of collision of each bunch, N is the number of particles in the positron (+) and electron (-) bunches, σ is the beam size in the horizontal (x) and vertical (y) directions, γ is the normalized beam energy, ε is the beam emittance, β is the beta function (cm) at the collision point for each plane and θ is the crossing angle. The Piwinski angle is φ =θσz/σx. The Super-B accelerator consists of two asymmetric energy rings, colliding in one Interaction Region (IR) at a large horizontal angle, with a spin rotator section in the HER to provide longitudinal polarization of the electron beam at the IP. In order to have equal tune shifts for the two beams, asymmetric B-Factories operate at unbalanced SPARX 1 stage SuperB LINAC SPARX future SLAC-PUB-14656 SLAC National Accelerator Laboratory, Menlo Park, CA 94025 beam currents, with a current ratio inverse to the energy ratio. For SuperB, with an energy ratio of 7/4 and a large crossing angle, new conditions for having equal tune shifts are possible. LER (+) and HER (-) beams can have different emittances and β* but equal currents: