Project of Booster Synchrotron for Duke Fel Storage Ring*

In this paper we present a project of a Booster-injector for the Duke FEL storage ring. The Booster will provide full energy injection into the storage ring at energy from 0.25 to 1.2 GeV. The Duke storage ring FEL (SR FEL) operates in lasing mode with 193-700 nm wavelength range [1,2]. This range will be extended into VUV in near future [3,4]. The geometry of the Duke SR FEL provides for head-on collision of e-beam and FEL photons. This mode of operation is used for High Intensity γ-ray Source (HIγS facility) generating intense beams of γ-rays from 1 MeV to about 200 MeV (currently from 2 MeV to 58 MeV). Generation of γ-rays with energy exceeding 20 MeV causes the loss of electrons, which will be replaced by new electrons from the Booster, operating in a top-up mode. The Booster has a robust FODO lattice. In this paper we present the design of the Booster and its magnetic elements. For 2D and 3D magnet design of the magnetic elements we used MERMAID 2D/3D code [6]. 1 BOOSTER LATTICE AND DESIGN The full-energy Booster-Injector is the standard approach for modern accelerator facilities. Boosters are notorious for being robust and reliable injectors into modern storage rings. The technology of booster-injectors (i.e. fast ramping rings) is well developed. The proposed Booster-Injector will provide for effective, full energy top-off injection into HIγS facility at operation energies from 0.25 GeV to 1.2 GeV [5]. It will transfer the electron bunches into the Duke storage with the repetition rate required for compensation of the lost electrons. The shortest ramping cycle is about 1.5 sec. We will use the existing 250 MeV linac to inject into the Booster. The linac-to-booster transport line will re-use many of the existing vacuum components and magnets We chose the robust FODO lattice for the booster ring to simplify its operation and to keep its cost modest. The Booster has a race-track shape. Two arcs are separated by 4.5 m long straight sections used for the RF cavity, the injection and the extraction kickers and septums. Each arc consists of 6 bending magnets with parallel edges, 4 focusing and 3 defocusing quadrupoles. They form a simple, and a very stable FODO lattice. The booster has double bilateral symmetry. The major cost-saving requirement of fitting the Booster into the existing North-East corner of the storage Table 1: Main parameters of the Booster (at 1.2 GeV) Maximum beam energy [GeV] 1.2 Injection energy [GeV] 0.25 Average beam current [mA] 100 Circumference [m] 28.544 Bending radius [m] 2.27 RF frequency [MHz] 178.55 Number of bunches 8 17 Energy rise rate [sec] 1 – 2 Beam emittance εx, εy [nmrad] 330/ 15 Maximum βx/ βy/ ηx [m] 24.6/10.2/1.6 Betatron tunes Qy/ Qx 0.46/ 2.41 Momentum compaction factor 0.148 Natural chromaticities Cy/ Cx -2.3/ -2.4 Damping times τx,y/ τs [mS] 2.83 / 1.42 Energy loss per turn [KeV] 80.7 Magnetic System: Dipoles: ea./ Bmax [T]/ Leff [m] 12/ 1.76/ 1.19 Quadrupoles: QF1: ea./ Gmax [T/m]/ Leff [m] 4/ 27.2/ 0.149 QF2: ea./ Gmax [T/m]/ Leff [m] 4/ 19.5/ 0.149 QD1: ea./ Gmax [T/m]/ Leff [m] 4/ 8.4/ 0.142 QD2: ea./ Gmax [T/m]/ Leff [m] 2/ 11.2/ 0.142 ring room imposes limitations on its structure and parameters. Table 1 lists the major parameters of the Booster. Figure 1 shows its layout. β-functions and ηfunction for half of the ring are shown in Figure 2. All main booster magnets (the dipoles and the quadrupoles) will be powered in series by one power supply. Figure 1: Layout of the Booster-Synchrotron. *This work is supported by the Dean of Natural Sciences, Duke