Peter N. Ostroumov, Physics Division, Argonne National Laboratory

1. Optimized design of triple-spoke superconducting resonator for application in high-power accelerators Peter N. Ostroumov, Physics Division, Argonne National Laboratory Kwang-Je Kim, University of Chicago Mark Champion, Fermilab ANL-FNAL Collaboration Meeting, June 27, 2008

2. Triple Spoke Resonators (TSR) • Proposed by K. Shepard (ANL) in 2002 • First publication to show all benefits of TSRs: • High-Energy Ion Linacs Based on Superconducting Spoke Cavities, K. W. Shepard, P. N. Ostroumov, and J. R. Delayen, Phys. Rev. ST – AB 6, 080101 (2003). • Two types of TSRs (beta=0.5 and beta=0.62) were developed and tested for FRIB (Facility for Rare Isotope Beams) • In the velocity range from 0.4c to 0.7c TSRs provide: • High Q and high accelerating gradients (demonstrated at ANL) • Excellent mechanical stability, minimizing the difficulty of tuning and phase control in the presence of microphonics or/and dynamic Lorentz detuning. Requires optimized design. • High shunt impedance – reduced cryogenic load • Low frequency – large longitudinal acceptance, reduced sensitivity to phase errors in the cavity resonance control • Low shunt impedance of HOM: very attractive for high-current FEL (beta=1) • Being considered for application in variety of projects worldwide

3. Project X Linac structure Major Linac Sections Front end ILC, beta=0.81 Standard ILC 325 MHz 1300 MHz Will be installed in the Meson Lab (60 MeV) SSR-2 420 0.065 2.5 10 33 0.065 2.5 10 33 0.05 2.5 10 32 110 110 123 410 410

4. ANL TSR performance 345 MHz • CW operation • Residual resistance is ~5 n (2K), Accelerating field is10 MV/m • Mechanical design is optimized to reduce • Very low microphonics (=1.04 Hz) • Not optimized to reduce Lorentz detuning ~7.3 Hz/(MV/m)2 • Fast tuners (piezoelectric and magnetostrictive) were demonstrated

5. A1 B1 A2 B2 FNAL 325 MHz TSR, optimized to reduce surface fields • Electrodynamics optimization by Ivan Gonin (FNAL)

6. Proposed tasks • Optimize mechanical design of the 325 MHz pulsed TSR • include helium vessel, coupling ports • Minimize Lorentz detuning • Locate best place for the slow and fast tuners • Improve electrodynamics design • Keep surface fields at minimum for given accelerating gradient • Iterate mechanical and electrodynamics design • Develop mechanical design of the resonator (the second year) for pulsed operation and application in Project X • Incorporate into the resonator design: • Slow tuner • Fast tuner • High-power coupler

7. Preliminary studies of the new TSR design using ANSYS Deformations in the1/8th of the model, symmetries applied Thermal contraction (300K 2K) Helium pressure Helium vessel

8. To achieve the proposed tasks • Build collaboration in the specific area of triple-spoke resonators and engage collaborators at UChicago, Fermilab and Argonne • Use broad ANL experience in development, construction and test of TSRs • Engage ANL Nuclear Engineering Division for thermal, structural analysis and mechanical design of the TSR • Use FNAL experience in design, construction and test of a single-spoke resonator for HINS • Enhance accelerator physics R&D in UoC • Involve students and post-doc for the optimized design of triple spoke resonators