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CLIC_DDS study 30.11.2010

Vasim Khan X-Band RF Structures, Beam Dynamics and Sources Workshop, Cockcroft Institute 30.11.10 2/24

CLIC_DDS Study Collaboration

• Vasim Khan

• Alessandro D’Elia

• Roger Jones

• Alexej Grudiev

• Germana Riddone

• Vadim Soldatov

• Walter Wuensch

• Riccardo Zennaro

University of Manchester and Cockcroft institute, U.K.

CERN, Switzerland

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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 optimisation summaryCircular Circular cell

ε=0.82

ε=1.38

Manifold-damped single cell

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 KPin= 70.8Eacc_UL=131 MV/mSc=6.75 W/μm2

RF-beam-eff=23.5%

∆T

35*Sc

Esur

Eacc

Pin

Dashed curves : Unloaded conditionSolid curves: Beam loaded condition

CLIC_G Values

Esur=240 MV/m∆T = 51 deg.Pin= 63.8Eacc_UL=128 MV/mSc=5.4 W/μm2

RF-beam-eff=27.7%

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CLIC_DDS_A: Dipole properties24 cellsNo interleaving

Qavg ~1700

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High Phase Advance Structures

cosψ 2sinψ ψ

E sinψ 4

ω/cR/Q

RP

2acc

2

2A

absg

g

v

v

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

NLC: DS1 a = 4.23 mm

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: CLICDDS_A and DDS_HPA

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120deg.Γx = 0.0126

Cell # 1a=4.0 mm, t=4.0 mm

150deg.Γx = 0.021

Cell # 1a=4.0 mm, t=3.2 mm6.1~

150

120Q

QΓ

1α Q

Dipole mode properties

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DDS_HPA

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RF parameters Unit DDS_A DDS_HPA42 DDS_HPA32

Phase advance / cell Deg. 120 150 150

Iris thickness mm 4/1.47 3.2/2.8 3.2/2.8

Bunch population 109 4.2 4.2 3.2

Q (In / Out) - 5020 / 6534 6931/7045 6931/7045

R’ (In / Out) MΩ/m 51 / 118 72.4/102.4 72.4/102.4

vg/c (In / Out) % 2.07 / 1.0 2.1 / 0.45 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 51 48

Emaxsur MV/m 220 234 225

Scmax W/μm2 6.75 5.9 5.5

RF-beam efficiency % 23.5 29 23.3

Comparison: 120 vs 150

Vasim Khan X-Band RF Structures, Beam Dynamics and Sources Workshop, Cockcroft Institute 30.11.10 14/24

DDS_HPA: Merits and Demerits

Reduction in dipole bandwidth from 2.1 GHz to 1.8 GHz

1. Necessary to reduce bunch population to satisfy wakefield constrains

2. Luminosity reduction

Reduced input power Less power absorbed

during breakdown Kick factors reduced Better dipole coupling

Cost efficient ?

Merits Demerits

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Enhanced damping: Eight manifoldsFour regular and four additional manifolds

Significant coupling

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Cell parametersa = 4.3 mmt = 2.6 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

Fundamental mode propertiesQ=7080R’/Q=10.356 (kΩ/m)vg=2.44 (%c)Es/Eacc=2.22Hs/Eacc=4.3 (mA/m)Sc/Eacc=5.45 x 10-4 (W/μm2/Eacc2)

Dipole mode properties

fsyn=16.1 GHz

Cell # 1

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Cell parametersa = 2.5 mmt = 2.8 mmRc = 8.8 mmMr = 2.0 mmMc = 15.1 mmvg=0.32 (%c)

Cell # 24

fsyn=17.89 GHz

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Lowest dipole mode propertiesΔf=2.25 σ=1.78 GHzΔf/fc= 10.5 (%c)

Two Cell result Need improvement

Vasim Khan X-Band RF Structures, Beam Dynamics and Sources Workshop, Cockcroft Institute 30.11.10 19/24

Regular manifold

Additional manifold

Damping material

εr=13tanδ=0.02NMr=2.8Damp_r=1

Eight manifolds and SicAs the coupling in the last cell is poor it is important to enhance coupling by optimising the last cell

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Cell # 24 :NMr=2 .8 Damp_r=1.0

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Accelerating modeNMr=2 .8 Damp_r=1εr=14 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

• 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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Vasim Khan X-Band RF Structures, Beam Dynamics and Sources Workshop, Cockcroft Institute 30.11.10 27/24

Cell # 1

Cell # 24

Cell # 1

Cell parametersa = 4.6 mmt = 2 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mmvg = 3.6 (%c)

Fsyn~15.76 GHz

Cell # 24

Cell parametersa = 3.3 mmt = 3 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mmvg = 0.95 (%c)

Fsyn~17 GHz

Four manifolds

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Cell # 1Cell parametersa = 4.6 mmt = 2 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

vg = 3.6 (%c)Fsyn~15.77 GHz

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Cell # 24

Cell parametersa = 3.3 mmt = 3 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

vg = 0.95 (%c)

Fsyn~17 GHz

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Cell # 1Cell parametersa = 4.6 mmt = 2 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

vg = 3.6 (%c)Fsyn~15.77 GHz

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Cell # 24

Cell parametersa = 3.3 mmt = 3 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

vg = 0.95 (%c)

Fsyn~17 GHz

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Cell # 1 :NMr=2 .8 Damp_r=1.0

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Cell # 1Cell parametersa = 4.6 mmt = 1 mmRc = 9.0 mmMr = 2.0 mmMc = 15.1 mm

vg = 4.84 (%c)Fsyn~15.65 GHz