Recent progress on Chokemode damped accelerating structures for

Recent progress on Choke-mode damped accelerating structures for the CLIC main linac Jiaru Shi Department of Engineering Physics, Tsinghua University 2013. 06. 30 HG 2013, Trieste, Italy

Outline Review of Choke mode design RF measurement Wakefield experiment High power test plan X band production at Tsinghua Acknowledgment Collaboration with CLIC study Accelerating Group in Tsinghua Ph. D student: ZHA, Hao

New choke design CDS-C Features include “two-section”, 1. 6 mm 2. 0 mm 1. 2 mm “impedance matching”, “detuning”

Damping result Freq( GHz) Q (R/Q )⊥ 15. 7 5. 4 80. 3 18. 6 6. 9 63. 2 23. 7 3. 8 14. 8 28. 4 12. 4 10. 9 38. 2 11. 6 9. 9 s CDS WDS Fc 1 1 Frms 4 5 Fworst 25 20 W⊥ (s=0. 15 m) V/m/mm/p. C WDS 5 CDS-A ~30 CDS-C 4~5

Load design � 15 GHz~40 GHz <-20 d. B； �ε μ tanδ error<10%, dimension error <5% �Into 4 pieces

Material Si. C Ferrite 28. 5 GHz：ε=11. 2+2. 3 j；μ=1。 18 GHz：ε=12；μ=2. 4+0. 5 j。 a=b=9. 5 mm; c≤ 0. 25 mm a=b=7 mm; c≤ 0. 3 mm Im(ε) ≥ 1. 8 Im(μ) ≥ 0. 4

RF measurement �Check the load �Check the reflection of the Choke �Calibrate the connector

Calibration with multiple short � x: refl. from coaxial (measured) � y: refl. from radial line (calc. ) � s 11, D, s 22: to be solved ……

Calibration result

Measurement of absorption curve � CDS-A agrees very well � 2 -section choke agrees �(no peak up to 40 GHz, trend OK) � Errors from “multi-short” calibration � espcially low frequency end (<15 GHz)

Measurement of absorption curve �Think-neck choke �CDS-C choke, second zero-point at 42 GHz

Reflection from Si. C Promising (<-20 d. B) Error over 30 GHz Future: plastic absorber only for RF measurement d. B f/GHz

bunch excitation to measure the damping @ AWA, ANL �Structure can be moved, driven by step motor �Offset to excite dipole modes, pickup RF signal �(No witness bunch at the moment)

Experiment (2) �Time domain signal with fast scope (0~36 GHz) �With -30 d. B attenuation signal strengh ~1 V/n. C/mm；

Experiment(3) 3 cells with Si. C 3 cells without Si. C RF probe installed

Expected signal � 0~20 GHz Scope，20 GHz mixer to get signal within 0~40 GHz � attenuation：about 40 d. B �probe-chamber 5 d. B; � 10 m cable 10~15 d. B �Mixer 15 d. B � 1 nc, 1 mm off-axis, 1 mm 2 loop size probe Frequency Q-factor Peak transverse kick Signal at probe 15. 7 GHz 10~20 75 V/p. C/m/mm 37 V 18. 6 GHz 10~20 80 V/p. C/m/mm 47 V 24 GHz 10~20 15 V/p. C/m/mm 12 V 28 GHz 15~20 25 V/p. C/m/mm 22 V 37 GHz 15~20 30 V/p. C/m/mm 35 V All dipoles N/A 240 V/p. C/m/mm 160~170 V Accelerating mode ~1000 524 V/p. C/m 0. 29 V

Single-cell SW test structure Single cell standing wave 1 C-SW-A 3. 75 -T 2. 6 -CHOKE 1. 6 [Ref: V. Dolgashev] To test breakdown behavior in the Choke Also test un-damped to compare RF design ready, Hope to be tested at KEK

Full structure optimization CDS-C Parameter CDS-C CLIC-G a(mm) 3. 15, 2. 35 Q(Cu) 4895, 5385 5538, 5738 Zs(MΩ/m) 59, 83 81, 103 vg(%c) 1. 38, 0. 73 1. 65, 0. 83 Esurf(MV/m) 245 235 Sc (MW/mm^2) 5. 66 5. 39 Delta T(K) 23. 0 47. 5 Pin (MW) 67. 5 60. 5 Filling time(ns) 75. 4 64. 8 RF-beam eff. 23. 8% 27. 5%

After Optimization �Wakefield checked �Fc=1. 01; Frms=3; Fworst=40 CDS-C CDS-D CLIC-G a(mm) 3. 15, 2. 35 3. 49, 2. 50 3. 15, 2. 35 Zs(MΩ/m) 59, 83 53, 74 81, 103 vg(%c) 1. 38, 0. 73 2. 00, 0. 75 1. 65, 0. 83 Ne/bunch(10^9) 3. 72 4. 50 3. 72 Esurf(MV/m) 245 223 235 Sc(MW/mm^2) 5. 66 5. 17 5. 39 Delta T(K) 23. 0 22. 0 47. 5 Pin (MW) 67. 5 79. 3 60. 5 Filling time(ns) 75. 4 60. 8 64. 8 RF-beam eff. 23. 8% 26. 0% 27. 5% FOM 7. 8 8. 3 9. 2

X-band Production at Tsinghua Univ. Assembly exercise Take CERN/VDL disks and follow the procedure Etching/Cleaning Bonding test in 1 bar H 2 Inspection X-band Power Extractor

Etching/Cleaning Before Etching 5 sec After

Flatness measurement before and after Etching 65 nm Note: different scale 400 nm

Bonding Leak check OK cut into halves One piece inspection at CERN

Inspection at CERN Ultrasound test OK Crossing grains at bonding plain Improvement: Boundary condition Pressure 0. 1 MPa Precise Temperature

A X-band (Copper) Power Extractor for ANL disks brazing. (no HOM damping) mode-launcher

Full structure production Full structure assembly T 24 pieces from CERN bonding/brazing at Tsinghua Tuning at Tsinghua @11. 424 GHz, Test at KEK (short period, quick check)? Disks fabricated at Tsinghua Choke-mode disks

Summary RF design and damping study Choke-mode damped structure design RF measurement on a radial choke Beam excited wake measurement **High power study required Structure production T 24 disks for bonding test T 24 full structure assembly Full structure production Full choke-structure production Small X-band test stand in the future

Thank you!

Backup slides Metallic X-band Power Extractor At 11. 7 GHz for RF power extraction at Argonne Wakefield Accelerator Disk-loaded strucure