The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement Double Quarter Wave Crab Cavity Qiong Wu On behalf of the DQWCC team 11/14/2012

Outline 11/14/12 2 Current Design Cavity parameters Higher Order Mode (HOM) damping Stiffening Helium Vessel Fabrication Status Future plan Summary

The Double Quarter Wave Crab Cavity 11/14/12 3 Crabbing (fundamental) mode freq. 1 st HOM Cavity length Cavity width Beam pipe diameter Deflecting voltage Unit MHz cm MV DQW crab cavity

Cavity Dimensions 11/14/12 4 unit: mm

Cavity Field 11/14/12 5 Electric field (left) and magnetic field (right) of fundamental mode.

Cavity Parameters 11/14/12 6 UnitDQWCC Fundamental Mode FrequencyMHz400 Nearest Mode FrequencyMHz579 Vertical Deflection VoltageMV3.3 Rt/Q (Fund. Mode)Ohm400 EpeakMV/m48** BpeakmT67** VacckV1.7 Energy ContentJ13 **Might have some decrease in electric field on the cavity and increase of magnetic field at the port opening (ACE3P) B E

HOMs 11/14/12 7 deflection mode longitudinal mode horizontal mode HOM Damping Electric field

HOM couplers 11/14/12 8

HOM Damping 11/14/12 9 HOM frequency [GHz]Mode Config.R/Q [Ω]Qext 0.579Longitudinal Horizontal Hybrid (y, z)0.24/ Deflection Horizontal6.02e Horizontal Longitudinal Deflection Horizontal1.84e Deflection Horizontal5.07e Hybrid (y, z)8.0e-2/6.0e Deflection

Stiffening 11/14/12 10 Nb property: RT: 1.03e11 Pa Cryo: 1.23E11 Pa Poisson’s Ratio: 0.38 Pressure: 2e5 Pa (2 bar) outside vacuum inside. Fixed Support: One side of beam port. Nb property for reference: Density: 8.58e-3 g/mm^3; Yield-RT: 4.83e7 Pa (7e7 Pa for 300 RRR Nb) Yield-Cryo: 5.77e8 Pa. Crab cavity max stress intensity vs Nb thickness (bare cavity only)

11/14/12 11 Stiffening Cont’d Stiffening plates and frames are added to the cavity for vertical cold tests. The material for stiffening components can be either Nb or Ti. The thickness of the stiffening plates is 4 mm, and the frame is 25 × 25 mm^2 in cross section. The only welding needed is the straight section on top and bottom of the stiffening plates.

11/14/12 12 Cavity stress simulation for 2e5 Pa (2 bar) outside + vacuum inside. Courtesy of Luís Alberty

Mechanical design of stiffening 11/14/12 13 Stiffening material: Ti Nb to Ti transition by serrated surface plus SS bolts SS bolts and pins at frame connections

Helium Vessel 11/14/12 14 Preliminary design of the helium vessel The vessel will play a role in stiffening the cavity Clearance for other beam lines in the vicinity. Simple machining and welding Compact design which saves LHe

11/14/12 15 Cavity stress simulation for 2e5 Pa (2 bar) outside + vacuum inside.

Fabrication Status 11/14/12 16 Courtesy of Niowave Inc.

Plan for /14/12 17 The design of the cavity is complete. Fabrication of the cavity with stiffening frame is in progress. We expect the fabrication to be complete at the end of calendar year Chemistry and HPR will be done right after the fabrication of the cavity. Vertical testing, first without HOM couplers then with HOM couplers will be carried out through early The testing will be focused on o Deflection voltage o HOMs o Peak fields o Possible multipacting

Prototype fabrication and testing 11/14/12 18 Fabrication and testing of the cavity and its various RF couplers (FPC, pick-up, HOM) will include:  Cavity fabrication  HOM coupler (two units)  Fundamental Power Coupler and pickup  Chemistry and HPR  Vertical testing (2 rounds)  LLRF DQWCC project BNL: Qiong Wu, Binping Xiao (Postdoc), John Skaritka, Vito De Monte, Sergey Belomestnykh, Ilan Ben-Zvi, Silvia Verdu Andres (Postdoc starting in Jan. 2013) Collaboration & Support: Rama Calaga (CERN), Luís Alberty (CERN), Zenghai Li (SLAC)

Summary 11/14/12 19 The DQWCC can provide high deflection voltage in a very compact dimension. The peak surface field of the cavity is in a safe level at the target deflecting voltage. It is optimized for LHC installation so that no conflict to the adjacent beamlines. The fabrication of the cavity will finish before the end of 2012, and pre-testing treatments will start right after. Large separation between fundamental deflection mode and 1 st HOM simplifies the design in HOM damping scheme and high-pass filter design. Close collaboration with other LARP participants profits greatly to the cavity design and fabrication. We are looking forward to testing the prototype Nb cavity in the year of 2013.

Acknowledgement Work supported by the US LHC Accelerator Research Program (LARP) through US Department of Energy contracts DE-AC02-07CH11359, DE-AC02-98CH10886, DE-AC02- 05CH11231, and DE-AC02-76SF /14/12 20

Reference 11/14/12 21 Q. Wu, et. al., HOM Damping and Multipacting Analysis of the Quarter-wave Crab Cavity, Proceedings of IPAC12, New Orleans, LA, May 20-25, 2012 R. Calaga, et. al., A Quarter Wave Design for Crab Crossing in the LHC, Proceedings of IPAC12, New Orleans, LA, May 20-25, 2012 Q. Wu, presentation, LARP CM18/HiLumi LHC Meeting, Fermi Lab, May 7-9, 2012 Q. Wu, S. Belomestnykh, I. Ben-Zvi, Novel deflecting cavity design for eRHIC, Proceedings of SRF11, Chicago, IL, July 25-29, 2011 R. Calaga, presentation, LHC-CC11, CERN, Nov 14-15, 2011 I. Ben-Zvi, presentation, LHC-CC10, CERN, Dec 15-17, 2010