CLIC choke mode structure and X-band activities in Tsinghua University.

Damping resultFreq(GHz)Q(R/Q)15.75.480.318.66.963.223.73.814.828.412.410.938.211.69.9sCDSWDSFc11Frms45Fworst2520

W (s=0.15m)Beam dynamic requirements< 6.6WDS5CDS-A20~30+Two section & Thin-neck10~17+Matching step7~10+Dipole detuning (CDS-C)5~6Experimental results. Click hereOutlineReview of Choke mode designRF measurementWakefield experimentOn progressing and future planOther X-band activities at Tsinghua last year

AcknowledgmentCollaboration with CLIC studyCollaboration with AWA (ANL) and Euclid Lab. Accelerating Group in TsinghuaOverview of CDS design

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

1.6mm1.2mm2.0mmS11S12 Absorbed by loadFrom CDS-C to CDS-DOptimized on distributions of iris size on each cell.Using genetic algorithm.W (0.15m)~4V/pC/m/mm;Fc=1.01; Frms=3.8; Fworst=35.

CDS-CCDS-DCLIC-GIris aperture(mm)3.15, 2.353.49, 2.503.15, 2.35Iris thickness(mm)1.67,11.7,1.481.67,1Shunt impedance(M/m)59, 8353, 7481, 103Group velocity(%c)1.38, 0.732.00, 0.751.65, 0.83Bunch population (109)3.724.503.72Max E-field(MV/m)246223235Sc* (MW/mm^2)5.725.175.45Pulse heating(K)23.222.047.9Peak input power(MW)67.479.360.2Filling time(ns)72.460.862.2RF-beam efficiency (%)24.226.028.1

* Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)From CDS-C to CDS-DCDS-CCDS-DCLIC-GIris aperture(mm)3.15, 2.353.49, 2.503.15, 2.35Iris thickness(mm)1.67,11.7,1.481.67,1Shunt impedance(M/m)59, 8353, 7481, 103Group velocity(%c)1.38, 0.732.00, 0.751.65, 0.83Bunch population (109)3.724.503.72Max E-field(MV/m)246223235Sc* (MW/mm^2)5.725.175.45Pulse heating(K)23.222.047.9Peak input power(MW)67.479.360.2Filling time(ns)72.460.862.2RF-beam efficiency (%)24.226.028.1

CDS-CCDS-D* Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)RF measurementsRadial line experiments are applied to:test the reflection of RF load (SiC pieces)verify HOMs absorption in choke structureCalibration using multi-short load (> 3).

To VNAPlace RF load

S11S12 absorbed in the loadRadial line experiments

Using Agilent E8364B VNA,10MHz~50GHz. (Equipments supported by Department of Electronic Engineering, Tsinghua University)

Calibration error and resultsReflection of RF loadMaterial EcasicP, provide by CERN.Results are promising (lower than -20dB).

a=b=9.5mm,c=0.1mm

HOMs absorption in choke

Frequency of Parasitic mode

Matching stepsIncrease the absorptionWakefield experiment at AWA(ANL)

G2 (Witness) beam line: 15MeV, 1~100nC G3 (Drive) beam line: 75MeV, >100nCCan produce Bunch trainG1 beam line: laser trigger breakdown experiment

1#2#3#4#oscilloscopeSet up experimentsGUNLINACChamberICTICTSpectrometerG2 Beam line set up for CLIC-choke-mode experiments

Be windows50.4um thicknessFor 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: 5.5mmSet up experiments

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

Experimental results

Low-band Dipole modeat 16GHz and 19GHzLooks like the dipole mode at 50-22=28GHz

Fundamental mode Unidentified

Q (@12GHz)=160~400Q (@16GHz)=12.5Q (@19GHz)=15.3Signal of cable 3#;10dB Attenuator, No mixer;Frequency and Q results are good!

On progressing and future planSingle 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?

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

Assembly and Tuning (Later)

An X-band (Copper) Power Extractor for ANL

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

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

21Wakefield measurement results

L0 No Mixer CABLE Attenuation 1# 30 dB 2# 20 dB 3# 10 dB 4#0 dB