Low Field Magnets with High Temperature Superconductors for an Upgrade of Cesr*#

An upgrade to the CESR electron-positron storage ring is being considered in which the single ring machine is replaced with two rings capable of storing high currents to provide high luminosity symmetric electron-positron collisions. This paper considers the implementation of the two rings using dual bore quadrupoles fabricated with high temperature superconductors (HTS). The use of HTS provides the required high current density needed to achieve the small (81 mm) inter-beam spacing, with a simpler and more efficient cryogenic system than would be required with conventional low-temperature superconductors. Concepts for the quadrupole magnetic and cryostat design are discussed. A concept for dipole magnets using Nb3Sn, integrated with a warm beam tube vacuum system, is also discussed. 1 MOTIVATION FOR THE DUAL-BORE SUPERCONDUCTING QUADRUPOLE The requirement for closely-spaced dual bore quadrupoles in the two ring symmetric collider[1] arises from the desire to minimize, as much as possible, the separation of the beams in the two rings. In the current design , the two beams share all the dipoles in the ring. The width of the dipoles, and consequently their cost and complexity, is thus minimized by keeping the beam centerlines relatively close together. The limited space available in the existing tunnel for the new rings provides an additional motivation to keep the overall dipole and quadrupole cross section small. Furthermore, the difficulties of beam separation as the beams emerge from the interaction region is minimized with a small beam separation. The goal for the beam-to-beam separation in the current ring design, 81 mm, requires a sufficiently high current density that a normal-conducting solution would have prohibitively large operating costs. Thus a superconducting coil design is the only practical and affordable choice. 2 DUAL-BORE QUADRUPOLE DESIGN