OPTIMIZATION OF ORBITS, SRF ACCELERATION, AND FOCUSING LATTICE FOR A STRONG-FOCUSING CYCLOTRON K. Melconian # , J. Gerity, J. Kellams, P. M. McIntyre, A. Sattarov, S. Assadi, Texas A&M Universi- ty, College Station, TX 77845 USA N. Pogue, Paul Scherrer Institute, Villigen, Switzerland Abstract The strong-focusing cyclotron is an isochronous sector cyclotron designed to accelerate >10 mA CW beams of protons and ions up to >500 MeV/u with low loss and high efficiency. Superconducting RF cavities are used to provide enough energy gain per turn to fully separate or- bits, and arc-shaped beam transport channels in the sector dipole apertures provide strong focusing of all orbits. A design methodology is being developed to optimize the sector dipoles, the focal lattice, and the SRF cavities so that betatron tunes can be locked to favorable operating point. Provision is made for correction of dispersion and chromaticity. The methodology will provide a framework on which we can then proceed to study and optimize the nonlinear beam dynamics for high-current transport. INTRODUCTION The Accelerator Research Laboratory at Texas A&M University is developing a strong-focusing cyclotron (SFC) for applications requiring high-current beams or micro-emittance beams [1]. Applications include an 800 MeV, >10 mA proton driver for accelerator-driven fission to destroy the transuranics and burn to completion the depleted uranium in spent nuclear fuel [2], a 100 MeV, >10 mA p/ driver for cost-effective production of medi- cal isotopes [ 3 ], and a 100 MeV spallation driver for fast neutron damage studies [4]. A 100 MeV SFC is shown in cutaway in Figure 1. It con- tains 4 superconducting RF cavities [5] that provide enough energy gain to fully separate successive orbits (r>6 cm). Each sector dipole consists of a warm-iron flux return with a pair of cold-iron flux plates suspended in the mid-plane gap to define the magnetic field B(r) required for isochronicity [6]. An array of arc-shaped beam transport channels (BTCs, shown as blue in Figure 1) are located in the aperture between the flux plates, each aligned to define the equilibrium trajectory for one orbit in that sector [7]. Each BTC contains an F-D quadrupole doublet and a dipole correction winding, all fabricated as wire-wound superferric windings on a square beam chan- nel. 80% of the 6 cm orbit spacing is available for parti- cle trajectories. In a previous study [8], we made a first design for a 100 MeV SFC and simulated several aspects of single-bunch dynamics of high-current proton bunches. That study validated that the SFC should be capable of accelerating >10 mA of CW beam without limitations from the effects that are known to limit beam current at PSI. The SFC design builds upon an earlier design for a sep- arated-orbit cyclotron, TRITRON [9], which also used SRF cavities and quadrupole channels. Although TRITRON successfully demonstrated transport of beam through several orbits, the orbit separation was small (10 mm) and the fraction of aperture with usable field quality for orbits was ~40%. In order to avoid this limitation, the beam transport channels in the SFC have been designed with > 6 cm orbit separation and 4 cm good-field aperture in each BTC. Table 1: Main Parameters of the SFC Design Proton energy (inj/ext) 13/100 MeV RF frequency 117 MHz Orbit radius (inj/ext) m Dipole field (inj/ext) 0.60/0.45 T Figure 1: 100 MeV SFC, with cutaway to show SRF cavi- ties and beam transport channels. ___________________________________________ *This work supported by the George and Cynthia Mitchell Foundation. #KarieMelconian@tamu.edu Slot-geometry half-wave cavity MgB 2 beam transport channel Ion sources 2.5 MeV RFQ 13 MeV IH structure choppers THPF135 Proceedings of IPAC2015, Richmond, VA, USA ISBN 978-3-95450-168-7 4038 Copyright © 2015 CC-BY-3.0 and by the respective authors 4: Hadron Accelerators A13 - Cyclotrons