International Workshop on Higher-Order-Mode Damping in Superconducting RF Cavities. 701 Clark Hall, Cornell University, October 11-13, 2010.

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1 Internatinal Wrkshp n Higher-Order-Mde Damping in Supercnducting RF Cavities 701 Clark Hall, Crnell University, Octber 11-13, 2010 Agenda Agenda Mnday, Octber 11, :00 9:15: Welcme (M. Liepe) 9:15 11:00: HOM damping requirements fr varius prjects Sessin chair: I. Ben-Zvi Task: Cllect key HOM specs fr different prjects. HOM damping requirements fr SRF deflecting cavities (A. Nassiri, 15 min) Higher rder mde damping cnsideratins fr the SPL cavities at CERN (W. Weingarten, 15 min) HOMs in the Prject X linac (V. Yakvlev, 15 min) HOM damping requirements fr varius prjects (all, 30 min ttal) Bunch length, bunch charge, beam current, number f cavities Cavity frequency, number f cells, lngitudinal lss factr at design bunch length Single bunch HOM pwer spectrum Average HOM pwer per cavity (k*q b *I) Wrst case peak HOM pwer per cavity in case f resnant excitatin f mdes Required damping (typical Q-values nly!) f mnple, diple, and quadruple mdes Discussin: HOM damping requirements (all, 30 min ttal) 11:00 11:30: Intrductin t HOM damping Sessin chair: I. Ben-Zvi A cmparisn f the HOM damping efficiency fr varius SRF cupler schemes (F. Marhauser, 30 min) 11:30 1:00 PM: Wrking lunch

2 1:00 5:00 PM: Antenna/ lp HOM cuplers Sessin chair: J. Knblch HOM Damper and Filter Design fr 56MHz SRF Cavity fr RHIC (Qing Wu, 20 min) HOM Damping Prperties f Fundamental Pwer Cuplers in the Supercnducting Electrn Gun f the Energy Recvery LINAC at Brkhaven Natinal Labratry (L. Hammns, 20 min) Capacitive-Antennae HOM Damper (H. Hahn, 20 min) New HOM cupler design fr High Current Supercnducting cavity (W. Xu, 20 min) Experience with 3.9 GHz lp cuplers (T. Khabibulline, 20 min) Heating in DESY style HOM cuplers in cw peratin (J. Sekutwicz, 20 min) Heating f HOM lp cuplers in CW mde (W.Anders/A.Neumann, 20 min) HOM damping variatins in SRF cavities (F. Marhauser, 20 min) Optimizatin f HOM Cuplers using Different Time Dmain Schemes (C. Ptratz, 20 min) Cmputatin f Cupler Damping Prperties in Cncatenated Arrangements (H.-W. Glck, 20 min) Discussin: antenna based HOM damping (all, 40 min) Cupling t high frequency mdes? Measured and/r simulated HOM Q-values fr given cavity design vs. frequency (n BBU simulatin results!) Cupling t mnple, diple, and quadruple mdes Hw many antenna/lp cuplers are required per cavity t guarantee effective damping fr all plarizatin angles? Design and results frm DESY, TJNAF, BNL Maximum HOM pwer handling and extractin Estimate f the heat lad t ~2K and all ther intercept temperatures at full HOM pwer Cupling t the fundamental mde and suppressin Thermal limitatins, e.g. lng pulse vertical test (DESY), cwversin fr the CEBAF upgrade cavities High thermal cnductin feedthrughs Nibium r Cu antenna? Impact n cst? Filter design and tuning, especially with large number f cuplers per cavity. Reliability/ success rate? Filter always needed? Cleanness challenges and slutins Field emissin Trap sulfur during EP? Extra beamline length required per cavity (cmpared t linac withut HOM damping) Mechanical / fabricatin challenges and slutins FNAL experience at 3.9 GHz and SNS experience Multipacting Mechanical failure Cst vs. design and material chices Nibium vs. nrmal cnducting Filter design and cmplexity Cabling; lad inside ur utside f vacuum vessel? Other challenges, limitatins and slutins

3 Tuesday, Octber 12, :00 10:00 AM: Waveguide HOM damping Sessin chair: S. Belmestnykh Waveguide HOM damping studies at JLAB (R. Rimmer, 30 min) Discussin: waveguide HOM damping (all, 30 min) Cupling t high frequency mdes? Measured and/r simulated HOM Q-values fr given cavity design vs. frequency (n BBU simulatin results!) TJNAF designs and results Maximum HOM pwer handling and extractin Estimate f the heat lad t ~2K and all ther intercept temperatures at full HOM pwer Cupling t the fundamental mde and suppressin Cleanness challenges and slutins Cleaning f waveguide sectins Extra beamline length required per cavity (cmpared t linac withut HOM damping) Mechanical / fabricatin challenges and slutins Cst vs. design and material chices Supercnducting r nrmal cnducting waveguide sectins? Number f waveguides per cavity required Length f waveguide sectin Absrber inside r utside f vacuum vessel? Water cling vs. crygens; risks invlved Temperature f lads at end f waveguides Shielding f IR radiatin frm warm lad Water cling and mechanical cavity vibratins Other challenges, limitatins and slutins 10:00 12:00 PM: RF absrbing materials Sessin chair: M. Liepe RF absrber studies at Crnell, part 1 (V. Shemelin, 20 min) RF absrber studies at Crnell, including DC cnductivity, part 2 (E. Chjnacki, 20 min) RF absrber studies at KEK (M. Sawamura, 20 min) Measurements f absrber materials frm rm temperature t 2K (F. Marhauser, 20 min) Discussin: HOM absrbing materials (all, 40 min) Rm temperature and crygenic material cmplex mu & eps (temperature dependence f absrptin) f varius dissipative materials vs. frequency (ferrites, ceramic with carbn, CNT ) DC cnductivity f dissipative materials and its temperature dependence Mechanical and thermal prperties f dissipative materials Vacuum prperties f dissipative materials Catings and ther methds t avid electrstatic charging f dissipative materials Fabricatin f dissipative materials and reliability f achieving specs Fabricatin cst f different dissipative materials

4 12:00 1:30 PM: Wrking lunch 1:30 5:30 PM: Beamline HOM lads Sessin chair: M. Liepe Ferrite HOM Lad Surrunding a Ceramic Break (L. Hammns, 20 min) Absrbing materials fr beamline absrbers: Hw gd is gd enugh? (Nick Valles, 20 min) Experience with the Crnell ERL beamline absrber prttype and future plans (E. Chjnacki, 30 min) Resnant HOM lad made f a resistive material (V. Shemelin, 20 min) Test f the Beam Line Absrber at FLASH (J. Sekutwicz, 20 min) Cling test f HOM absrber mdel fr cerl in Japan (M. Sawamura, 30 min) Operatin Experience f HOM absrbers at KEKB (T. Furuya, 20 min) Beamline absrber wrk at Mun Inc (R. Jhnsn, 20 min) Design and Applicatin f the High-Efficiency HOM Absrbers at PEP-II (A. Nvkhatski, 20 min) Discussin: beamline absrbers (all, 40 min) Measured and/r simulated HOM Q-values fr given cavity design vs. frequency (n BBU simulatin results!) Crnell, DESY, BNL, KEK designs Maximum HOM pwer handling and extractin What is the ptimal perating temperature? Heat transfer and thermal cnnectins Estimate f the heat lad t ~2K and all ther intercept temperatures at full HOM pwer Cupling t the fundamental mde and suppressin Cleanness challenges and slutins Cleaning f absrber materials Risk f particle generatin? Hw t quantify the absence r presence f RF absrber material particulate generatin that culd spil the Q f nearby SRF cavities? Catings? Extra beamline length required per cavity (cmpared t linac withut HOM damping) Mechanical / fabricatin challenges and slutins Are bellw sectins between cavities needed / desirable? Heat intercept and static heat lads t cavities Brazing, sldering, metallizatin f ceramics/ferrites t heat sinks. Absrber tiles vs. rings Accurate mechanical mdeling that includes plastic defrmatin f material. Cst vs. design and material chices Thermal matching f heat sinks t ceramic/ferrites Cpper cating f beam pipe sectins r stainless steel? Other challenges, limitatins and slutins

5 Wednesday, Octber 13, :00 10:15 AM: RF simulatin tls (2D, 3D) Sessin chair: E. Chjnacki ACE3P and HOM pwer flw in the Crnell ERL (Liling Xia, 20 min) HOM simulatins with ANSYS (S. Psen, 20 min) Higher Order Mde Heating Analysis fr the ILC Supercnducting Linacs (C.r Nantista, 20 min) Discussin: HOM simulatins (all, 15 min) Which prblems need 3D mdels? Which prblems require nly 2D? Which 3D sftware allws cmplex mu & eps? Which 3D sftware is up t the jb? Which 2D sftware allws cmplex mu & eps? Which 2D sftware is up t the jb? FEM vs. FD cdes Hw high in frequency can/shuld ne g? Hw much can ne trust the simulatins? What safety factr shuld be included? Cmparisn f simulatins and measurements. Time dmain vs. frequency dmain Chice f bundary cnditins at cavity beam tube ends (pen, electric, magnetic). What is realistic fr a large linac installatin? 10:15 11:30 AM: Measurement Methds (HOMs, material prperties) Sessin chair: E. Chjnacki RF absrber studies using waveguides in transmissin (V. Shemelin, 20 min) HOM-BPMs at the 3.9 GHz Supercnducting Cavities fr FLASH and the Eurpean XFEL (R.M. Jnes, 20 min) Experiments n HOM Spectrum Manipulatin in a ILC 1.3 GHz Cavity (T. Khabibulline, 20 min) Discussin: HOM measurements (all, 15 min) Measurement methds f RF absrbing materials (cmplex mu & eps, mechanical prperties ) Crnell waveguide methd, terminated waveguide (TJNAF), resnatr methds, which methd gives reliable data at perating temperatures? DC cnductivity, mechanical and thermal methds 11:30 1:00 PM: Clseut Measurements in cavities and cavity prttypes (cpper) Hw much can ne trust HOM measurements n individual cavities? Bundary cnditins at beam tubes? Are cld measurements needed? Are beam measurements needed? Are cpper mdes needed? Summary f HOM damping schemes currently available and fully develped, including parameter specs (frequency range, pwer handling capabilities...) Summary f future, ptential perfrmance f imprved versins, including utstanding challenges/prblems, ptential slutins, and R&D Vlunteers t perfrm the R&D, the time frame, and reprt the results