CLIC choke mode structure and X-band activities in Tsinghua University. Jiaru Shi(Department of Engineering Physics, Tsinghua University) HaoZha (CERN) 2014.02.04 CLIC Workshop 2014
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
S12 Absorbed by load 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 2.0mm 1.2mm 1.6mm S11
Damping result Experimental results. Click here
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; • Fc=1.01; Frms=3.8; Fworst=35. * Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)
From CDS-C to CDS-D CDS-C CDS-D * Reference: Phys. Rev. ST Accel. Beams 12, 102001 (2009)
RF measurements S12 absorbed in theload • 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). S11 To VNA Place RF load
Radial line experiments • Using Agilent E8364B VNA,10MHz~50GHz. (Equipments supported by Department of Electronic Engineering, Tsinghua University) Calibration error and results
Reflection of RF load a=b=9.5mm,c=0.1mm • Material EcasicP, provide by CERN. • Results are promising (lower than -20dB).
HOMs absorption in choke Frequency of Parasitic mode Matching steps Increase the absorption
Wakefield experiment at AWA(ANL) oscilloscope 1# 4# 2# 3# G1 beam line: laser trigger breakdown experiment G3 (Drive) beam line: 75MeV, >100nC Can produce Bunch train G2 (Witness) beam line: 15MeV, 1~100nC
Set up experiments 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 Chamber Spectrometer GUN LINAC ICT ICT
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
Experimental results 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! Unidentified Fundamental mode Low-band Dipole mode at 16GHz and 19GHz Looks like the dipole mode at 50-22= 28GHz
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?
X-band structure assembly in Tsinghua • T24 pieces from CERN; • Bonding and brazing (testing): • Vacuum leak tested OK! • Assembly and Tuning (Later)
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.
Multiple short Calibration • x:refl. from coaxial (measured) • y:refl. from radial line (calc.) • s11,D,s22: to be solved ……