IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 22, NO. 3, JUNE 2012 4904404 Magnetic Design of the Advanced Light Source Harmonic Sextupoles A. Madur, C. Steier, D. Arbelaez, S. Marks, S. Prestemon, and R. Schlueter Abstract—Forty-eight harmonic sextupole magnets with in- tegrated dipole correctors and skew quadrupole coils will be introduced in the Advanced Light Source Storage Ring. These new magnets are required to allow the ALS to provide the 40 beamline users with higher photon beam brightness (factor of 2 or 3). Introducing new combined-function magnets in an existing storage ring is a challenge due to the limited space available and a balance had to be found between magnet performance and spatial constraints. Consequently four different magnet designs were required. The calculation and simulation results obtained for each design as well as the impact of the different design choices on the magnetic performance are developed in this paper. I. INTRODUCTION N EW MAGNETS will be introduced in the Advanced Light Source (ALS) storage ring (SR) to produce higher brightness photon beams for the users. This upgrade project is dedicated to the reduction of the horizontal emittance by a factor of 2 (undulator beamlines) or 3 (bend magnet beam- lines) [1]. Initial analysis to evaluate possible upgrade options was car- ried out in 2007 [2] and global optimization methods were used to demonstrate the possibility to reduce the beam emittance by only introducing new sextupole fields in the lattice [3], [4]. Introducing new magnets in an almost 20-year old SR, in- creased the number of design constraints considerably. These combined function magnets will indeed have to fit around ex- isting vacuum chambers (3 different cross section), to clear beamline equipment (40 beamlines) and to adapt to the ex- isting steering corrector power supplies. The upgrade consists in replacing the existing steering correctors by six-pole com- bined function magnets providing sextupole, vertical & hor- izontal steering, and skew quadrupole correction. This leads to the replacement of 46 magnets and the addition of 2 sex- tupole in the injection sextion to make the sextupole lattice symmetric. All these constraints and the design choices we made for these magnets are developed in [5]. The constraint analysis work then resulted in 4 different magnet designs that will allow the ALS to meet its objective of increasing the photon beam brightness. Manuscript received September 13, 2011; accepted January 12, 2012. Date of publication March 05, 2012; date of current version May 24, 2012. This work was supported by the Director, Office of Science, of the US Department of En- ergy under Contract No. DE-AC02-05CH11231. The authors are with Lawrence Berkeley National Laboratory, Berkeley, CA 94707 USA (e-mail: amadur@lbl.gov). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2012.2184514 Fig. 1. Top: Type E1 and E2; Bottom: Type F, Type G magnets. TABLE I FIELD STRENGTH REQUIREMENTS II. MAGNET DESIGNS A. General Characteristics Fig. 1 shows the four different designs that are planned to be installed. There will 21 type E1 magnets and 1 type E2 magnet in the straight sections, 2 type F magnets in the injection section and 24 type G magnets in the arc sections. All of the magnets except the type F will provide all the re- quired the field type at full strengths (Table I). Compromised requirements were set for the type F magnets as they will have a shorter core length (70 mm) to accommodate for the crowded injection area. These magnets will therefore provide a sextupole field only (no other correction) and its integrated strength will be 15 T/m compared to the full integrated sextupole field re- quirement of 19 T/m of the other magnets. Note that the 19 T/m of the new magnet sextupole integrated field strength is about 20% of the ALS existing sextupoles. B. Coil Design All the magnet coils will be made of square hollow copper conductor (4 4 mm and 2.5 mm diameter cooling channel). U.S. Government work not protected by U.S. copyright.