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
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Assumption: Kick on only following trailing bunch
D. Schulte, PAC09, FR5RFP055
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Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 3/17
A=
Kick on only following trailing bunch
a= A=Exp[a]
A=
a=
Kick on multiple bunches
Direct effect Direct and indirect effect
Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 4/17
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
Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 7/17
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
Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 12/17
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
Vasim Khan CLIC RF structure group meeting, CERN 07.03.2011 17/17
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