1. Status of the TTF-3 RF Power Coupler Activity Andrei Lunin, Ken Premo, Tug Arkan Feb. 2012

2. 2 Outline Introduction Overview of TTF3 coupler activity at Fermilab Improvements on coupler RF processing Review of Coupler Inspection and Processing Flow at SLAC and CPI Power coupler for XFEL Project Results & Outlook

3. Objective The TTF3 coupler was developed by the TESLA Collaboration and is being used for ILC cavity R&D. SLAC is providing TTF3 couplers for the cavities that are being ‘dressed’ at Fermilab. All couplers have been purchased from one vendor – CPI. 12 couplers ordered with tagging along to the DESY order. 10 couplers ordered by FNAL and sent to SLAC for processing 22 couplers ordered by SLAC directly using ARRA funds ------------------------------------------------------------------------------------------------------------------------------------------- Total = 44 couplers (SLAC received from CPI ) - 4 couplers didn’t pass incoming QC at SLAC and have NCR issues --------------------------------- 40 couplers has to be processed and send to FNAL To date, 22 couplers (11 pairs) were tested at SLAC and shipped to FNAL 1 coupler sent to KEK 1 coupler has slight vacuum leak (not confirmed by SLAC, in progress) 2 couplers in the box (just arrived) ---------------------------------- 18 couplers been tested at HTS facility as a part of the ILC cavity assembly - 4 couplers 2 failed to pass HTS test + 2 sent back to SLAC for re-cleaning. 1 coupler sent to KEK 9 couplers 8 on CM2 string + 1 CM3 candidate 4 couplers 1 on the shelf + 3 attached to cavities ------------------------------------ 18 couplers at SLAC and need to tested before Sept. 2012 3

4. TTF-3 coupler problems 2 cavities failed during the HTS tests in 2009 due to low gradient quench induced by field emission. Six meetings were held with SLAC and twice we visited to CPI to understood the root cause of these problems. The following issues were found and have been solved (√) or in progress (√) : Antenna concentricity (CPI developed a special fixtures) Rounding masking (raised CPI attention that improper masking could cause a copper flaking). Bolt&nuts materials (all CuNi fasteners replaced with Nitronic60) Cu-plating&bead blasting (bad copper adhesion detected, new plating technique (reverse polarity) is recommended to vendor) US cleaning procedure (millipore filtering was proposed as a test for plating quality, optimum time and US power level found ) RF processing (the SLAC parameters were unified with warm coupler conditioning at HTS in Fermilab ) Enhanced QC control (better boroscope inspection, bellows exercise, chemical analysis ) Weak RF contact in flange (capacitor ring replaced by a copper membrane)  The results were presented on SRF-2011 conf. and TTC meeting (Dec. 2011, Beijing) 4

5. TTF3 Coupler Warm RF Processing FERMILAB (SW regime) SLAC (TW regime) Output RF power range, [kW] 0 ÷ 2800 ÷ 1200 Input LLRF range, [dBm] -32 ÷ -2NA (control by modulator voltage) RF pulse width, [µs] 20, 50, 100, 200, 400 800, 1300 50, 100, 200, 400 800, 1100 RF signal ramp up +0.1 dBm every 30 s, +1 hour stay on top +20 kW every 10 s (< 400 µs) +40 kW every 10 s (≥ 400 µs) Minimum processing time 2100 steps, 24.5 hours 270 steps, ~ 0.75 hours TTF3 Couplers Warm RF Processing Time After the initial coupler RF processing at SLAC have been modified and a total processing time extended to 20 hours, the second coupler warm RF conditioning at HTS became more stable and it takes now about 30-40 hours in average. 5

6. SLAC TTF-3 Coupler TW Processing* (* Courtesy to Faya Wang, SLAC) Dry N 2 New RF processing (pair #9) 6

7. Replacement of the capacitor, SLAC RF Test SLAC will run long (100 hour) high power RF test in order to insure that new design provides a reliable solution 7

8. For further development, testing and conditioning of the TTF3 power coupler a collaboration between LAL and DESY has started since 2004. TTF3 Power Coupler modifications for XFEL Project TTF3 CouplerXFEL Coupler  4 diagnostic ports removed (PMT and infrared)  Additional reinforcement around bellows (special collars are hydroformed in a single piece)  Connections made by pull-out instead of cut&weld  Seals to improve the RF contacts  New 80K and 5K shields and connections  Motorized tuning added  Reduced numbers of parts (35 -> 23) and junctions (33 -> 21) Major design changes 8

9. Major technological changes Perfect Cu coating Electroplating process: DC current variable pulsed current pulsed current with reverse polarity Bath types: alkaline cyanide acid sulphate pyrophosphate Ceramic TiN coating Two different techniques: Vacuum evaporation Sputtering process under N2+Ar pressure EB or TIG (Tungsten Inert Gas) welding stainless to stainless Cu to Cu stainless to Cu 9 Back to brazing ? ()

10. Changes in QC Inspection and RF Test Assembly Additional manufacturing stages are demanded: Detailed visual inspection Cleaning and assembly onto the RF test stand Leak test In-situ baking after assembly while pumping QC map Boroscope inspection stand 10

11. Changes in RF Processing The conditioning procedure 7 stages defined by the pulsed length (from 20μs to 1.3ms) The RF power going to 1MW for the first 5 stages and 500kW for the last two. The power increase is controlled only according to the vacuum level Interlock safety based on e-pickup activity, arc occurrence, reflected power, ceramic temperature and vacuum level 11

12. Conclusions 1.The collaboration between FNAL and SLAC on TTF3 couplers production and testing is going on. The coupler delivery workflow crossed its midterm and it’s planned to be completed before Sept. 2012 2.List of problems have been solved successfully during the last 3 years in order to optimize coupler production and testing. 3.The major concern is the quality of the Cu coating in the cold part of the coupler. Further work with vendor on improvement of Cu-plating process is required. 4.The TTF3 power coupler for the XFEL project have been redesigned for the mass production and in order to minimize a risk of failure, guarantee a constant quality and reliability of all coupler components. 5.The TTF3 coupler enhancements proposed at Fermilab are similar to the XFEL coupler production recommendations. 12

13. Supplying new fasteners for CF-100 section (attaching the warm to cold parts) as the supplied fasteners (P/N S100453, M8X35 CuNi) failed during assembly. New fastener are Nitronic 60 and have a higher yield strength than the CuNi. 13