1. LCLS-II Power Coupler Nikolay Solyak, Ivan Gonin, Andrei Lunin C.Adolphsen - SLAC TTC meeting, March 23-27, 2014 AWLC2014, FNAL, May 12-16, 20141

2. ItemSpecComment DesignEuXFEL Coupler2009 Drawing Package with exceptions noted below Max Input Power7 kW CWAssume would run with full reflection Minimum Qext Foreseen1e7Allows 16 MV/m with no beam and 6.6 kW input, and allows 6 MW beams with 33 kW input Maximum Qext Foreseen5e7Match for 0.3 mA beams at 16 MV/m, 26 Hz BW Reduction in Antenna Length8.5 mmMaintain 3 mm rounding Range of Antenna Travel+/- 7.5 mmRange measured Predicted Qext Min Range Qext Max Range 3.6e6 – 4.7e6 – 7.5e6 1.0e8 – 1.1e8 – 1.5e8 Assuming +/- 5 mm transverse offsets Warm Section Outer Cond Plating10 um +/- 5 um, RRR = 30-80Nominal EuXFEL Warm Section Inner Cond Plating100 um +/- 10 um, RRR = 30-80Modified – Temp Rise < 150 degC for 14 kW Cold Section Outer Cond Plating10 um +/- 5 um, RRR = 30-80Nominal EuXFEL Center Conductor HV BiasOptionalUse flex copper rings that can be replaced with existing capacitor rings if HV bias needed Warm and Cold e-Probe ports reqNoDo not expect multipacting at low power Warm Light Port RequiredNoDo not expect arcs at low power Motorized AntennaYes – max step = 50 umChanges Qext by 1% RF Processing7 kW CW with full reflection – vary reflected phase by 180 deg For initial couplers, use pulse power processing at SLAC LCLS-II Coupler Technical Specs Preliminary AWLC2014, FNAL, May 12-16, 20142

3. Fundamental Power Coupler (FPC) XFEL (modified TTF3) coupler is not meet LCLS-II requirements – Tuning range (1.e6-1.e7) not cover required Q ext =4.e7 – Overheating of the internal bellow in warm section at 7kW CW power at full reflection (effective power ~14kW) Two modifications were proposed to address these problems (R&D program: Four coupler modification test ) – Cut antenna 8.5mm to increase Q ext – Increase copper plating of internal inner conductor of warm section from 30 μm to 100-150 μm to eliminate overheating TTF-3 design AWLC2014, FNAL, May 12-16, 20143

4. Inner conductor: Temperature distribution for different thickness of copper coating and different RRR (15kW, TW-regime) Copper plating at inner part is 100 microns Data is simulated for RRR=10 Conclusion: TTF3 Coupler need to be modified for LCLS-II. 100-150 μm Cu plating inner conductor in warm section of coupler is possible solution. T max limit AWLC2014, FNAL, May 12-16, 20144

5. 5 Q ext ~ 2.4·10 7 Antenna tip cut by 8.5 mm Q min Q nom Q max Original coupler1.10 6 3.5·10 6 1.8·10 7 Tip cut by 7 mm 3.8·10 6 1.6·10 7 8.5·10 7 Tip cut by 8.5mm 5.0·10 6 2.4·10 7 12·10 7 R3 A. Lunin, 12/13/13 Nominal positions R3 Original XFEL antenna Q ext ~ 4.0·10 6 LCLS-II Cavity Q ext Computation LCLS-II specs Q ext – range for ±7.5mm antenna tuning AWLC2014, FNAL, May 12-16, 2014

6. Conclusion For LCLS-II coupler the most sensitive parameter is a horizontal antenna shift/tilt. ± 5 mm shift change Q ext by -5%/+50%. Vertical tolerances are relaxed. Vert. antenna tilt (up and down) Horiz. antenna tilt along cavity axis Q min Q nom Q max Original coupler0.7·10 5 (3.0.. 6.5) ·10 6 3.0·10 7 Tip cut by 8.5 mm5.5·10 6 (2.3.. 3.8)*·10 7 1.2·10 8 XFEL LCLS-II XFEL Q ext sensitivity to antenna displacements (ILC vs. LCLS-II) A.Lunin Horizontal Vertical Horizontal AWLC2014, FNAL, May 12-16, 20146

7. TWTW power 2K, W4K, W80K, W T max  K TTF-III as is7kW0.131.2414.2404 Helium, 1atm7kW0.131.2717.3316 LCLS2 (100µm)7kW0.131.2515.5326 LCLS2; 100/200µm15kW0.262.2829.2/30425/356 Power Losses and max. Temp I.Gonin (FNAL) TTF-3 Coupler: Inner coating 30µm, outer coating 10µm. Helium, P=1atm Window force 160N Ivan Gonin, FNAL AWLC2014, FNAL, May 12-16, 20147 Helium cooling of the warm section 7kW TW TTF3 original coupler 7kW TW

8. Full reflection: E-field distribution in LCLS-II coupler, Q=4e7, P in =7kW AWLC2014, FNAL, May 12-16, 20148

9. L=0 LCLS-II Coupler. Inner coating 100µm. Outer coating 10µm Maximum Temperature vs. L On resonance Tmax ~425K Temperature distribution along surface of inner conductor for TW and SW ( L=0mm & L=65mm ) PEC BC L On resonance Off resonance Coupler operation at 7kW CW at full reflection AWLC2014, FNAL, May 12-16, 20149

10. 10 Coupler test in HTS -1 Operational for ~5 yrs (~2 cavity/month throughput) – 1.3 GHz and 3.9 GHz cavities, ~1.5 ms and 9ms RF pulses – Now HTS upgraded for CW operation (commissioning) – Priorities in FY14 (CW regime) HOM feedthu’s (XFEL and JLAB designs) 3 tests of high-Q0 dressed cavity (1 dressed to ILC helium vessel and 2 dressed to LCLS-II vessel) 2 modified at SLAC Power Couplers Integrated test of dressed cavity with Slow/Fast tuners, Frequency control and μ-phonics AWLC2014, FNAL, May 12-16, 2014

11. Active Magnetic shielding AWLC2014, FNAL, May 12-16, 201411 500 mGs - 500 mGs Inside 1-layer magnetic shielding Max magnitude < 45mGs Inside 1-layer magnetic shielding after active correction by coils Max magnitude < 6mG

12. HTS test preliminary schedule Test# and goals Start 2014 Cav. type Helium Vessel HOM antenna Couple (cold) Coupler (warm) Magn shield TunerRF 1:HTS commissioning, HOM feedthru, μ-phon nowRI26ILCXFELvariableNone1L+coilBlade50W 2: High Q0 cavity #1June 15AES11ILCnonvariableNone1L+coilNone50W 3: FPC cold modif, μ-phonics study July 1 RI26 or AES11 ILCXFEL FPC modif FPC He cooled 1L+coilbladeIOT 4: FPC modified; μ-phonics study July 25 RI26 or AES11 ILCJLAB FPC modif FPC#1 modif 1L+coilbladeIOT 5: High-Q cav. #2 FPC#1 Aug 20HQ#2LCLS-IIXFEL FPC modif FPC#1 modif 1L+coil No tuner IOT 6:High-Q#3 integrated FPC#2 Sept.20HQ#3LCLS-IIJLAB FPC modif FPC#2 modif 2-layer Lever tuner IOT 7: high-Q#2 integrated Tuner reliability Oct.15HQ#2LCLS-IIXFEL FPC modif FPC#1 modif 2-layer lever tuner IOT Assumptions about readiness: 2 modified “cold” parts of FPC: April (done) 2 modified “warm” parts of FPC: June 4 LCLS-II type of Helium Vessels: end of July JLAB feedthru: end of June New lever tuner and 2-layer shielding: Sept. AWLC2014, FNAL, May 12-16, 201412

13. Conclusion XFEL coupler not meet LCLS-II specifications. Problems: Q ext range and overheating 2 major modification was proposed: shorter antenna (by 8.5mm) and thicker (>100μm) Cu plating of inner conductor in warm section to address these problems: Modifications are in progress at SLAC (cold part modification was done, warm sections of couplers will be ready by the end of June 2014, plated at CPI and processed at SLAC). HTS tests is essential part of design verification program for LCLS-II. – 3 high Q0 (N2 doped) integrated tests, (HOM feedtru’s, FPC, Helium vessel, Tuner, magnetic shielding) – two modified FPC assembled on high-Qo cavity. Next step: start FPC procurement after HTS tests. – Documentations and review. AWLC2014, FNAL, May 12-16, 201413