Latest Design of ILC （ RDR)

1.3 GHz technology developed by TESLA Collaboration, R&D from 1992 to reduce the cost per MeV by a factor of 20 from current SCRF installations (CEBAF). Increased the operating accelerating gradient by a factor of 5 : ~5 MV/m to ~25 MV/m, Reduced the cost per meter by a factor of four for large-scale production. TESLA cavity R&D based on CERN, CEBAF (JLAB), Cornell University. KEK, Saclay and Wuppertal. Basic element of the technology is a nine-cell 1.3 GHz niobium cavity. Approximately 160 of these cavities have been fabricated by industry as part of R&D program at DESY. A Primary Cost Driver for ILC -- Superconducting RF Technology

Principle of 50MV/m Cavity shape designs with low Hp/Eacc TTF: TESLA shape Reentrant (RE): Cornell Univ. Low Loss(LL): JLAB/DESY Ichiro ｰ Single(IS): KEK TESLALLREIS Diameter [mm] Ep/Eacc Hp/Eacc [Oe/MV/m] R/Q [W] G[W] Eacc max

ICHIRO Cavity Goal ： 51 MV/m.

Fabricated Six ICHIRO Single Cells Electron Beam Welding (EBW) Both KEK in-house machine and industrial machine were used Six IS cavities were fabricated (IS#2, #3, #4, #5, #6, #7). Series of tests done to optimize KEK surface treatment. Deep-drawn Nb cups

Stones and water Rough stones Fine stones KEK CBP Rough stones + water : 4 hours x 3 times Removal thickness = 25 μm x 3 = 75 μm Fine stones + water : 4 hours x 3 times Removal thickness = 20 μm x 3 = 60 μm Total removal thickness = 135 μm. Centrifugal Barrel Polishing (CBP) Mechanical Grinding

Light Chemical Polishing (CP) HF(46%) : HNO 3 (60%) : H 3 PO 4 (85%) 1 :1 : 1 in volume CP for 1 minute at 25 O C. Removal thickness = 10 μm. Prepare smooth surface before EP. Annealing/Degassing in furnace 750 O C for 3 hours Degassing of hydrogen important. Temperature and time optimized for cavity softness and cost. Light Chemical PolishingAnnealing - Degassing

Measurement of and Unloaded Q-value Measure time constant for cavity to “ringing down” when RF switched off Accelerating Field Geometric Factor

Schematic of Experimental Setup Cavity in Cryostat Signal Generator Phase Locked Loop Q of Cavity is very large Power Meters 1.9K LHe

Re-Entrant Cavity - Best Eacc = 59 MV/m Cornell Surface preparation at KEK Vertical Cornell

International Collaborations （ ILC WG5-Asia ） Korea, PAL: Y. uk SOHN stayed Mar – Aug 2005 (WG5 Korea convener) Korea, Pusan Univ: CHO (student) stayed in Mar 2005 IHEP: Shi Hua (engineer) stayed Feb - Mar 2005 Canada, Toronto Univ: Prof. Robert ORR stays from Aug 2005 for 1 year LNL-INFN: Giullia LANZA (student) stays Jan – Mar Korea, CHEP, Kyungpook Univ.: Prof. Hyoung Suk KIM stayed Jan-Mar 2006 IHEP: GE Mingqi (student) stayed Jan– Mar 2006