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CLIC_DDS study
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CLIC_DDS Study Collaboration
University of Manchester and Cockcroft institute, U.K. CERN, Switzerland Vasim Khan Alessandro D’Elia Roger Jones Alexej Grudiev Germana Riddone Vadim Soldatov Walter Wuensch Riccardo Zennaro
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Outlook Summary of Optimisation: CLIC_DDS
Overview of test structure: CLIC_DDS_A High Phase Advance (HPA) Structures: Merits and Demerits CLIC_DDS_HPA Future of CLIC_DDS_HPA
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CLIC_DDS_C ∆f=3.6 σ =2.3 GHz ∆f/fc=13.75% Dipole mode Manifold mode
192 cells 8-fold interleaving Manifold mode Manifold Coupling slot ∆f=3.6 σ =2.3 GHz ∆f/fc=13.75% 24 cells No interleaving ∆fmin = 8.12 MHz ∆tmax =123 ns ∆s = m ∆fmin = 65 MHz ∆tmax =15.38 ns ∆s = 4.61 m 192 cells 8-fold interleaving
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DDS_C Fails to satisfy rf breakdown constraints!
Surface fields DDS_C Fails to satisfy rf breakdown constraints!
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CLIC_DDS optimisation summary
Circular cell ε=0.82 ε=1.38 Manifold-damped single cell Circular ε=1.38 DDS_E DDS_C DDS_E DDS_C
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CLIC_DDS_A: Monopole properties
Max. Values Esur=220 MV/m ∆T = 51 K Pin= 70.8 Eacc_UL=131 MV/m Sc=6.75 W/μm2 RF-beam-eff=23.5% ∆T 35*Sc Esur Eacc Pin Dashed curves : Unloaded condition Solid curves: Beam loaded condition CLIC_G Values Esur=240 MV/m ∆T = 51 deg. Pin= 63.8 Eacc_UL=128 MV/m Sc=5.4 W/μm2 RF-beam-eff=27.7%
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CLIC_DDS_A: Dipole properties
24 cells No interleaving Qavg ~1700
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CLIC_DDS_A: 24+2 cells mm
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Water pipes for cooling Vacuum flange
Power input Power output Tuning holes Cut-view Beam
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Profile accuracy VDL
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High Phase Advance Structures
1) Low group velocity → Less power absorbed during breakdown Ref: R.M. Jones, et. al., SLAC-PUB 8887 CLIC
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NLC: Band partitioning
a = 4.23 mm NLC: DS1 ψacc : 120°→ 150°:Lowest dipole kick factor reduces by ~ 20% Ref: R.M. Jones, et. al., SLAC-PUB 9467
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Fundamental mode Optimisation CLIC_DDS_HPA
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Band partitioning: CLIC DDS_A and DDS_HPA
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Dipole mode properties
120deg. Γx = Cell # 1 a=4.0 mm, t=4.0 mm 150deg. Γx = 0.021 Cell # 1 a=4.0 mm, t=3.2 mm
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DDS_HPA
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Comparison: 120 vs 150 RF parameters Unit DDS_A DDS_HPA42 DDS_HPA32
Phase advance / cell Deg. 120 150 Iris thickness mm 4/1.47 3.2/2.8 Bunch population 109 4.2 3.2 Q (In / Out) - 5020 / 6534 6931/7045 R’ (In / Out) MΩ/m 51 / 118 72.4/102.4 vg/c (In / Out) % 2.07 / 1.0 2.1 / 0.45 Eaccmax (L./UnL.) MV/m 105 / 132 93 .3/ 143 90/ 138 Pin MW 71 68.2 63.6 ∆Tmaxsur oK 51 48 Emaxsur 220 234 225 Scmax W/μm2 6.75 5.9 5.5 RF-beam efficiency 23.5 29 23.3
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DDS_HPA: Merits and Demerits
Reduced input power Less power absorbed during breakdown Kick factors reduced Better dipole coupling Reduction in dipole bandwidth from 2.1 GHz to 1.8 GHz Necessary to reduce bunch population to satisfy wakefield constrains Luminosity reduction Cost efficient ?
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Enhanced damping: Eight manifolds
Four regular and four additional manifolds Significant coupling
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Cell # 1 Cell parameters Fundamental mode properties
fsyn=16.1 GHz Cell parameters a = 4.3 mm t = 2.6 mm Rc = 9.0 mm Mr = 2.0 mm Mc = 15.1 mm Fundamental mode properties Q=7080 R’/Q= (kΩ/m) vg=2.44 (%c) Es/Eacc=2.22 Hs/Eacc=4.3 (mA/m) Sc/Eacc=5.45 x 10-4 (W/μm2/Eacc2) Dipole mode properties
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Cell # 24 Cell parameters a = 2.5 mm t = 2.8 mm Rc = 8.8 mm
Mr = 2.0 mm Mc = 15.1 mm vg=0.32 (%c) fsyn=17.89 GHz
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Two Cell result Lowest dipole mode properties Need improvement
Δf=2.25 σ=1.78 GHz Δf/fc= 10.5 (%c)
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Eight manifolds and Sic
As the coupling in the last cell is poor it is important to enhance coupling by optimising the last cell Regular manifold Additional manifold Damping material εr=13 tanδ=0.02 NMr=2.8 Damp_r=1
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Cell # 24 :NMr= Damp_r=1.0
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Accelerating mode NMr= Damp_r=1 εr= tanδ=0.04
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DDS_HPA_SiC SiC insertion in an 8-manifold cell improves damping
The SiC properites and dimensions are optimised for Cell # 24 This optimisation does not improve damping of Cell # 1 Due to SiC losses, multiple avoided crossings are observed Need some modification in circuit model to incorporate additional losses (SiC) (future work ?)
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Closing remarks CLIC_DDS_A is being fabricated
CLIC_DDS_A: High power test by 2011 end CLIC_DDS_HPA: 1) Coupling looks promising 2) Need to improve bandwidth To be investigated in detail: 1) Eight manifolds 2) DDS_SiC damping 3) Circuit model modification to incorporate SiC losses
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Acknowledgments Thank you
We have benefited from discussions with Juwen Wang, Zhengai Li and Toshiyasu Higo on X-band structures Thanks to Igor Syratchev for suggesting to investigate CLIC_DDS_SiC. Thank you
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Additional slides
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Four manifolds Cell # 24 Cell # 1 Cell # 1 Cell # 24 Fsyn~15.76 GHz
Cell parameters a = 3.3 mm t = 3 mm Rc = 9.0 mm Mr = 2.0 mm Mc = 15.1 mm vg = 0.95 (%c) Fsyn~17 GHz Cell # 1 Cell parameters a = 4.6 mm t = 2 mm Rc = 9.0 mm Mr = 2.0 mm Mc = 15.1 mm vg = 3.6 (%c) Fsyn~15.76 GHz Cell # 1 Cell # 24
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Cell # 1 Cell parameters a = 4.6 mm t = 2 mm Rc = 9.0 mm Mr = 2.0 mm
Mc = 15.1 mm vg = 3.6 (%c) Fsyn~15.77 GHz
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Cell # 24 Cell parameters a = 3.3 mm t = 3 mm Rc = 9.0 mm Mr = 2.0 mm
Mc = 15.1 mm vg = 0.95 (%c) Fsyn~17 GHz
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Cell # 1 Cell parameters a = 4.6 mm t = 2 mm Rc = 9.0 mm Mr = 2.0 mm
Mc = 15.1 mm vg = 3.6 (%c) Fsyn~15.77 GHz
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Cell # 24 Cell parameters a = 3.3 mm t = 3 mm Rc = 9.0 mm Mr = 2.0 mm
Mc = 15.1 mm vg = 0.95 (%c) Fsyn~17 GHz
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Cell # 1 :NMr= Damp_r=1.0
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Cell # 1 Cell parameters a = 4.6 mm t = 1 mm Rc = 9.0 mm Mr = 2.0 mm
Mc = 15.1 mm vg = 4.84 (%c) Fsyn~15.65 GHz
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