Conceptual Design of ILC Damping Ring Wiggler Straight Vacuum System

CONCEPTUAL DESIGN OF ILC DAMPING RING WIGGLER STRAIGHT VACUUM SYSTEM* S. Marks, K. Kennedy, D. Plate, R. D. Schlueter, M. Zisman, LBNL, Berkeley, CA 94720, U.S.A. Abstract The positron and electron damping rings for the International Linear Collider will contain long straight sections consisting of twenty wiggler/quadrupole pairs. The wigglers will be based upon the CESR superconducting design. There are a number of challenges associated with the design of the wiggler straight vacuum system, in particular, the absorption of photon power generated by the wigglers. This paper will present the overall conceptual design of the wiggler straight vacuum system developed for the ILC Reference Design Report. Particular emphasis will be placed on photon power load calculations and the absorber design. The first section of this paper presents a summary of the vacuum system conceptual design. The second section presents photon power load calculations and discuss the absorber design. VACUUM SYSTEM CONCEPT The wiggler straight vacuum system for the ILC damping rings consists of separate chambers for the wiggler and quadrupole sections. Fig. 1 shows a plan view layout of a portion of the wiggler straight. A cross-section of the wiggler chamber is shown in Fig. 2. The overall width and height of the chamber indicated in the figure represent dimensions compatible with the proposed wiggler and cryostat design. The chamber is a machined and welded aluminum unit, designed as a warm-bore insert, mechanically decoupled from the wiggler and cryogenic system. A NEG pumping system and photon absorber are incorporated in antechambers. Integral cooling is incorporated to minimize distortion of the chamber and thermal load on the wiggler cryostat during NEG regeneration. A TiZrV NEG surface coating will be used on the main chamber bore to minimize SEY [2]. Note that the eventual vacuum system design may utilized other surface coatings such as TiN as well as incorporate other technologies, such as clearing electrodes, to minimize SEY. INTRODUCTION The magnet lattice adopted for the International Linear Collider (ILC) positron and electron damping rings for the Reference Design Report (RDR) contains a total of eighty damping wigglers per ring. The wigglers are incorporated into four straight sections, which incorporate 21 quadrupoles and twenty wigglers centered between quadrupole pairs. The wigglers are based upon the CESR superconducting design [1]. The primary technical challenges for the wiggler straight vacuum system consist of dealing with the substantial power eradiated from the wiggler and minimizing the secondary electron yield (SEY) in order to meet emittance objectives for the positron ring. The former challenge was the primary focus of technical work on the vacuum system within the RDR phase. Techniques for SEY reduction provide a significant focus for current and future work. Table 1 summarizes the parameters relevant for the wiggler straight layout and radiated power load calculations. Table 1: Wiggler Straight Parameters Total Length of Straight (m) Quadrupole Spacing (m) Wiggler Length (m) Wiggler Period (m) Wiggler Field Strength (T) Number of Full Strength Poles Electron Energy (GeV) Current (A) Figure 1. ILC wiggler straight layout. The NEG pumping system will be similar to that designed for the PEP-II B Factory [3]. The assembly consists of NEG coated fins and an integral heating rod for regeneration. The estimated pumping speed for CO is 1000 liters/sec/m. With a total incident photon flux of 2×10 18 photons/s/m, the estimated yield of CO will be 2×10 13 molecules/s/m. This will result in an equilibrium CO partial pressure of 7×10 -10 Torr. *Work supported by the Office of Science, U. S. Department of Energy, under Contract No. DE-AC02-05CH112231