CLIC_Main Linacs Multi-bunch wake effect in various damping schemes

Vasim Khan07.03.2012

Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 2/17

2122 3802

NezWGeVmNezWEL

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Assumption: Kick on only following trailing bunch

D. Schulte, PAC09, FR5RFP055

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A=

Kick on only following trailing bunch

a= A=Exp[a]

A=

a=

Kick on multiple bunches

Direct effect Direct and indirect effect

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Wake @ bunch positions

TD26_vg1.8_discR05_CC: GdfidL simulations with PML

Envelope wake

Courtesy of Alexej Grudiev

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Amplification factors

Envelope wake

Wake

Envelope wake

Wake

Envelope wake

Wake

Kick on only first trailing bunch

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Envelope wake

Wake

Envelope wake

Wake

Envelope wake

Wake

Systematic errors in bunch spacing

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Random bunch shift: -1% to 1%

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Choke Mode

Choke Mode

TD26_discR05_CC

Courtesy of Jiaru Shi

Choke mode design

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nb311={Fc,Frms,Fworst}={357.924, 31.6057, 1094.08}

nb311={Fc,Frms,Fworst}={1515.58, 151.144, 6480.98}

Wake (with phase information)

Envelope Wake

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8 x DDS_Circular

DDS_A (Elliptical)Structure Wake (with phase information)

Fc Frms Fw

DDS_A 1.29 x 1024 1.25 x 1027 1.32 x 1028

8 x DDS_A 3.4 x 105 2.8 x 107 7.5 x 108

8 x DDS (Circular cells) 6573 5 x 106 1.55 x 108

CERN and Uni. Manchester + C.I. collaboration

DDS

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WW=7.5 WH =6.5 Wpos=14.5

Wpos

WW

WH

DDS _Hybrid : CLIC_G + Manifolds

Structure Wake (with phase information)

Fc Frms Fw

DDS_Hybrid (175 bunches) 4.38 x 105 4 x 108 2 x 108

No interleavingLinear tapering

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DDS_Hybrid

Cell Q vg/c R’/Q

Label -- % kΩ/m

First 5000 3.48 13.089

Mid 5053 3.02 14.569

Last 5156 2.43 16.134

TD26 (CLIC_G)

Cell Q vg/c R’/Q

Label -- % kΩ/m

First 5538 1.65 14.572

Mid 5637 1.2 16.227

Last 5739 0.85 17.932

H-H Boundary condition

DDS_Hybrid

E-H Boundary condition

DDS_Hybrid

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Comparison

Structure Wake (with phase information)Fc Frms Fw

TD26_WDS (120 bunches) 1.06 6 26

Choke mode (120 bunches) 80 15 1300

DDS_A* 1.29 x 1024 1.25 x 1027 1.32 x 1028

8 x DDS_A* 3.4 x 105 2.8 x 107 7.5 x 108

8 x DDS* (Circular cells) 6573 5 x 106 1.55 x 108

DDS_Hybrid (175 bunches) 4.38 x 105 4 x 108 2 x 108

* Only lowest dipole wake with 311 bunches is considered

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Remarks

• TD26 wake looks acceptable• Choke mode wake needs improvement. The 60 GHz (5th harmonic) mode detuning

will certainly improve the wake• For conventional DDS the wake is unacceptably high• For hybrid DDS with possible interleaving wake might improve. However,

fundamental mode rf parameters will get exacerbated

Thank you

Thank you A. Grudiev, J. Shi and A. D’Elia for providing the wake data andD.Schulte and A. Latina for helping me understand the matrix calculations

Acknowledgments

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Additional slides

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Envelope wakeWake

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Envelope wakeFor nb=312Wake on 120 bunchesFc=1.058Frms= 6.35Fworst= 28.51

WakeFor nb=312Wake on 120 bunchesFc=1.0087Frms= 3.0016Fworst= 15.61

Random bunch shift: -1% to 1%RMS = 0.5%

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Random bunch shift: -1% to 1%

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Systematic errors in bunch charge