SRF RD program for the Future Circular Collider

SRF R&D program for the Future Circular Collider On behalf of the FCC SRF WP Collaboration O Brunner #3 CERN SRF Workshop, 31 May – 1 June‘ 18, CERN

FCC study International FCC collaboration (CERN as host lab) to study: • • pp-collider (FCC-hh) e+e- collider (FCC-ee) -> as potential first step HE-LHC with FCC-hh technology p-e (FCC-he) option, IP integration, e- from ERL Numbers and challenges are BIG!: • FCC-hh: -> 16 (20) T magnets -> Stored beam energy 8. 4 [GJ] (~ 21 x LHC! enough to melt > 10 tons of copper) -> SR emitted by the beams ~ 100 to 1, 000 times LHC • FCC-ee: -> SR 50 MW per beam ->RF power to the beam -> ~ 150 – 170 MW of electrical power -> up to ~ 11 GV of RF voltage

FCC-ee L J B RF FCC-hh RF H D F 1 tunnel, 2 different arrangements • FCC-ee: machine + booster • FCC-hh: machine + injector chain F. Valchkova-Georgieva et al.

FCC-ee parameters 4 energy setups in 2 categories: • • High current: -> low voltage and high current, i. e. Z and W (FCC-hh) High energy: -> low beam current and high accelerating voltage, i. e. H and tt. Selection of 3 cavity sets to cover all options (machine & booster): • high intensity (Z, FCC-hh) -> 400 MHz single-cell cavities, ~1 MW source • the cavity design must be carefully optimized with regard to higher order modes (HOM) • higher energy (W, H): 400 MHz 4 -cell Nb/Cu cavities • HOMs are still a challenge! BUT good acceleration efficiency required • tt machine complement: 800 MHz 5 -cell cavities based on bulk Nb • high acceleration efficiency, shorter footprint, smaller waveguide (radiation protection)

FCC-ee staging scenario Construction in 5 steps: • sequential 8 months of operation /4 months winter shutdown (hardware upgrades) • interesting physics at each energy steps with required luminosity • 1 year-long shutdown to allow for ttbar upgrade • installation sequence comparable to LEP ( ≈ 30 CM/shutdown) • Z machine hardware can be re-used for FCC-hh

Cavity and HOM coupler designs optimization of accelerating cavities & HOM couplers • • cavity design beam – cavity interaction S. Gorgi Zadeh et al. I. Karpov et al. Innovative crab cavity design (WOW cavity) • • open waveguide: excellent HOM damping, low Z well suited for Nb/Cu technology -> coating feasibility under study (TE/VSC) RF quadrupole resonator for Landau damping • Performing design compared to double-QWR and RF dipole cavity A. Grudiev et al.

High efficiency klystron Increasing energy efficiency & reducing energy demand critical for future accelerators (FCC, ILC, CLIC, . . ) High Efficiency International Klystron Activity led by CERN since 2013 (HEIKA) • new code “Kly. C-2 D”, cross-checked with other platforms -> very fast, reliable and free! • development of new klystron bunching technologies with increased efficiency • prototype for high efficiency CSM tube I. Syratchev, J. Cai

Cavity material & performance Nb/Cu - breakthrough performance Total cryogenic power in MW for FCC-ee ttbar G. Rosaz et al. A. Sublet, 14: 40 – 15: 00 today Thin Film deposition techniques for SRF M. Martinello et al. G. Rosaz, 16: 00 - 16: 15 today Hi. PIMS A. Miyazaki, 11: 15 - 11: 30 tomorrow Review of LHC cavity cold tests S. Aull et al. (2016) Advances with Nb 3 Sn • • Nb 3 Sn/Nb by Sn diffusion (Cornel, Fermilab) -> good result at 1. 3 GHz, ready to go at 800 MHz magnetron sputtering of Nb 3 Sn thin films on copper (TE/VSC) -> high quality films produced K. Ilyina-Brunner , 16: 15 - 16: 30 today A 15 coatings

Innovative cavity fabrication techniques additive manufacturing with Nb • • 802 MHz bulk Nb cavity (Jlab) complex shapes with cooling channels excellent density (powder choice is crucial) superconductivity confirmed post-processing of parts significantly improves: • purity • surface roughness R. Gerard, 09: 45 - 10: 00 tomorrow Developments for SRF equipment with additive manufacturing F. Marhauser et al Field-emission on-set from ~20 MV/m Multipactor free F. Gerigk 15: 00 – 15: 20 today High gradient program new methods for cavity fabrication • seamless 400 MHz aluminium prototype (INFN-LNL) C. Pira et al. • electro Hydro-Forming (Bmax / EN/MME) C. Abajo et al.

Characterization of Nb superconducting films on copper quadrupole resonator (BE-RF) • Measurement of , penetration depth, quench field (high T), thermal conductivity, RRR M. Arzeo et al. V. Del Pozo Romano, 17: 00 – 17: 15 today QPR II FIB microscopy (focused ion beam) (EN-MME) • Microstructural characterisation of SRF cavity coatings A. Lunt et al.

Copper electro-polishing studies Substrate IS CRITICAL! • Past experience proves that copper electro-polishing provides superior accelerating performances if compared with copper chemical polishing -> copper electro-polishing facility soon available at CERN (TE/ VSC) L. Marques Antunes Ferreira, 16: 30 – 16: 45 today Surface Chemistry

AM Valente Feliciano, FCC week 2018