The Next Linear Collider Damping Ring Complex

Abstract

THE NEXT LINEAR COLLIDER DAMPING RING COMPLEX * J. Corlett † , D. Atkinson, S. De Santis, N. Hartman, K. Kennedy, D. Li, S. Marks, Y. Minamihara, H. Nishimura, M. Pivi, D. Reavill, R. Rimmer, R. Schlueter, A. Wolski, LBNL, Berkeley, CA, USA S. Anderson, B. McKee, T. Raubenheimer, M. Ross, J. C. Sheppard, SLAC, Stanford, CA, USA Abstract We report progress on the design of the Next Linear Collider (NLC) Damping Rings complexes. The purpose of the damping rings is to provide low emittance electron and positron bunch trains to the NLC linacs, at a rate of 120 Hz. As an option to operate at the higher rate of 180 Hz, two 1.98 GeV main damping rings per beam are proposed, and one positron pre-damping ring. The main damping rings store up to 0.8 amp in 3 trains of 190 bunches each and have normalized extracted beam emittances γe x = 3 mm-mrad and γe y = 0.02 mm-mrad. The optical designs, based on a theoretical minimum emittance lattice (TME), are described, with an analysis of dynamic aperture and non-linear effects. Key subsystems and components are described, including the wiggler, the vacuum systems and photon stop design, and the higher- order-mode damped RF cavities. Impedance and instabilities are discussed. Table 1: Parameters for the Main Damping Ring and Positron Pre-Damping Ring. Circumference (m) Max. Current (A) Bunch trains x Bunches per train x Bunch separation (ns) ν x , ν y , ν s γe x equilib. (mm-mrad) γe x extract. , γe y extract. (mm-mrad) σ e (%), σ z (mm) ξ x uncorr. , ξ y uncorr τ x , τ y , τ e (ms) MDR 3 x 190 x 1.4 PPDR 2 x 190 x 1.4 2.95 x 10 -4 7.05 x 10 -3 INTRODUCTION The NLC damping ring complexes provide damping of the e + /e - beams from the sources, producing stable, low- emittance beams which pass on to bunch length compressors and pre-acceleration before entering the main linacs [1]. The main damping rings of both e + /e - systems are identical. Due to the large emittance of positrons produced from the target, a pre-damping ring is required to reduce the e + beam emittance to be accommodated by the main damping ring acceptance. Each ring will store multiple trains of bunches at once, and a single fully damped bunch train is extracted while a new train from the source is injected. The repetition rate is 120 Hz, although options to operate at 180 Hz have been explored. U sr (kV/turn) α p V RF (MV), Frequency (MHz) Lattice 36 TME cells 16 TME cells sources and the B-Factories in that they must store high current beams (~ 1A) while attaining small emittances, low vacuum pressure, and large synchrotron radiation power loading. Many design and technology issues for Electron complex DESIGN The damping ring designs use Theoretical Minimum Emittance (TME) arc cells, with a racetrack layout in which damping wigglers, RF systems, feedback systems, a circumference adjustment chicane, and injection/ extraction hardware are located in the long straights. Damping wigglers are required to provide the necessary damping at 1.98 GeV, given a 120 Hz injection/extraction rate and the extracted beam emittance requirement. General discussion of design criteria are given in [2], and details of the current lattice designs in [3]. Principal parameters of the rings are listed in Table 1. The rings resemble third-generation synchrotron light Positron complex Figure 1. Damping rings layouts, showing e + and e - complexes at the ends of the main linacs. Work supported by the US DOE under contract DE-AC03- 76SF00098 (LBNL), and DE-AC0376SF00098 (SLAC) jncorlett@lbl.gov