1. Jiaru Shi(Department of Engineering Physics, Tsinghua University) Hao Zha (CERN) 2014.02.04 CLIC Workshop 2014 CLIC choke mode structure and X-band activities in Tsinghua University.

2. Outline Review of Choke mode design RF measurement Wakefield experiment On progressing and future plan Other X-band activities at Tsinghua last year Acknowledgment Collaboration with CLIC study Collaboration with AWA (ANL) and Euclid Lab. Accelerating Group in Tsinghua

3. Overview of CDS design NameDescriptionParametersManufactory & Measurement CDS-AOriginal design; regular choke; Prototype cells made in CERN CDS-BHOM tuned choke; Wakefield suppression Improve; No CDS-CNew choke design, Optimized on wakefield suppression; Prototype cells (aluminium) made in Tsinghua. Wakefield tested in AWA(ANL). CDS-DNew choke design; Optimized on RF parameters. No

4. New choke design (CDS-C) Improved features include: “Two section” design: avoid parasitic mode (~30GHz) “Thin-neck” design and “matching” design: reduce reflection of HOMs from choke. “Dipole detuning” design: detune two low-band dipole modes in one cell 1.6mm 1.2mm 2.0mm S 11 S 12 Absorbed by load

5. Damping result Freq( GHz) Q(R/Q ) ⊥ 15.75.480.3 18.66.963.2 23.73.814.8 28.412.410.9 38.211.69.9 sCDSWDS FcFc 11 F rms 45 F worst 2520 W ⊥ (s=0.15m) Beam dynamic requirements < 6.6 WDS5 CDS-A20~30 +Two section & Thin- neck 10~17 +Matching step7~10 +Dipole detuning (CDS-C) 5~6 Experimental results. Click here

6. From CDS-C to CDS-D Optimized on distributions of iris size on each cell. Using genetic algorithm. W ⊥ (0.15m)~4V/pC/m/mm; F c =1.01; F rms =3.8; F worst =35. CDS -C CDS -D CLI C-G Iris aperture(mm)3.15, 2.35 3.49, 2.50 3.15, 2.35 Iris thickness(mm)1.67, 1 1.7, 1.48 1.67, 1 Shunt impedance(MΩ/m) 59, 83 53, 74 81, 103 Group velocity(%c) 1.38, 0.73 2.00, 0.75 1.65, 0.83 Bunch population ( 10 9 ) 3.724.503.72 Max E- field(MV/m) 246223235 Sc* (MW/mm^2)5.725.175.45 Pulse heating(K)23.222.047.9 Peak input power(MW) 67.479.360.2 Filling time(ns)72.460.862.2 RF-beam efficiency (%) 24.226.028.1 * Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)

7. From CDS-C to CDS-D CDS -C CDS -D CLI C-G Iris aperture(mm)3.15, 2.35 3.49, 2.50 3.15, 2.35 Iris thickness(mm)1.67, 1 1.7, 1.48 1.67, 1 Shunt impedance(MΩ/m) 59, 83 53, 74 81, 103 Group velocity(%c) 1.38, 0.73 2.00, 0.75 1.65, 0.83 Bunch population ( 10 9 ) 3.724.503.72 Max E- field(MV/m) 246223235 Sc* (MW/mm^2)5.725.175.45 Pulse heating(K)23.222.047.9 Peak input power(MW) 67.479.360.2 Filling time(ns)72.460.862.2 RF-beam efficiency (%) 24.226.028.1 CDS-C CDS-D * Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)

8. RF measurements Radial line experiments are applied to: test the reflection of RF load (SiC pieces) verify HOMs absorption in choke structure Calibration using multi-short load (> 3). To VNA Place RF load S 11 S 12 absorbed in the load

9. Radial line experiments Using Agilent E8364B VNA,10MHz~50GHz. (Equipments supported by Department of Electronic Engineering, Tsinghua University) Calibration error and results

10. Reflection of RF load Material EcasicP, provide by CERN. Results are promising (lower than -20dB). a=b=9.5mm,c=0.1mm

11. HOMs absorption in choke Frequency of Parasitic mode Matching steps Increase the absorption

12. Wakefield experiment at AWA(ANL) G2 (Witness) beam line: 15MeV, 1~100nC G3 (Drive) beam line: 75MeV, >100nC Can produce Bunch train G1 beam line: laser trigger breakdown experiment 1#2#3#4# oscilloscope

13. Set up experiments GUNLINAC Chamber ICT Spectr omete r G2 Beam line set up for CLIC-choke-mode experiments Be windows ： 50.4um thickness ； For 14MeV electron beam, ~30% (calculated by Fluka) of the beam can pass it without any scattering. Optimized on beam dynamics: 1nC Beam size: ~0.7m, 5nC Beam size: ~1.6m, Beam aperture: 5.5mm

14. Set up experiments Aluminium cells, SiC load (reproduced in U.S.). Coaxial RF cable (0.59mm outer radius, magnetic probe) 20GHz oscilloscope, 0~20GHz mixer

15. Experimental results Low-band Dipole mode at 16GHz and 19GHz16GHz and 19GHz Looks like the dipole mode at 50-22= 28GHz Fundamental modeUnidentified Q (@12GHz)=160~400 Q (@16GHz)=12.5 Q (@19GHz)=15.3 Signal of cable 3#; 10dB Attenuator, No mixer; Frequency and Q results are good!

16. On progressing and future plan Single cell SW structure to test breakdown behavior in the choke. Hope to tested in KEK. 6-cell choke-mode structures with tuning manufacturing in Tsinghua. Full structure for high-gradient test will be developed later. Two beam experiments?

17. X-band structure assembly in Tsinghua T24 pieces from CERN; Bonding and brazing (testing): Vacuum leak tested OK! Assembly and Tuning (Later)

18. An X-band (Copper) Power Extractor for ANL

19. Infrastructure update for X-band Cleaning room for high gradient structure (plus a new 40GHz VNA); Upgrade of H-furnace for brazing: More precisely control for temperature in real time.

20. Thank you

21. Multiple short Calibration x:refl. from coaxial (measured) y:refl. from radial line (calc.) s11,D,s22: to be solved ……

22. Wakefield measurement results L0L0 No Mixer CABLEAttenuati on 1#30 dB 2#20 dB 3#10 dB 4#0 dB