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CERN - IT DepartmentCH-1211 Genève 23
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Separating dipolar and quadrupolar wakes with
Mafia
Andreas Wagner (IT/IS) 8th SPS impedance informal meeting
Wednesday 17/12/2008
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Overview
• Transverse Wakefield Properties
– Axially Symmetric Structures– Non- Axially Symmetric Structures– Numeric calculation of Wakefield components
Presentation title - 2
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Axial Symmetric Structures
• Pillbox cavaity
Presentation title - 3
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Axial Symmetric Structures
• Energy Loss vs beam offset
Presentation title - 4
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Axial Symmetric Structures
• Magnitude of wake field depends on displacement of source charge and is independent of test charge position !
Presentation title - 5
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Axial Symmetric Structures
• Transverse kicks vs test charge position
Presentation title - 6
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Non-axially-symmetric structures
• Elliptic Model of LEP Shielded bellows
Presentation title - 7
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CERN - IT DepartmentCH-1211 Genève 23
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Non-axially-symmetric structures
• Elliptic Model of LEP Shielded bellows
Presentation title - 8
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CERN - IT DepartmentCH-1211 Genève 23
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Non-axially-symmetric structures
• Transverse kicks vs test charge position
Presentation title - 9
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Non-axially-symmetric structures
• Generalized Impedance
Presentation title - 10
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Non-axially-symmetric structures
• Transverse kicks for on axis beam:
• Ansatz: Subtract this wake for beams with finite offset !
Presentation title - 11
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CERN - IT DepartmentCH-1211 Genève 23
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Non-axially-symmetric structures
• Transverse kicks vs test charge position minus contribution of on-axis beam
Presentation title - 12
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Non-axially-symmetric structures
• The major difference to axially symmetric structures is this offset dependent "quadrupolar“ wake potential acting on a trailing particle:
Presentation title - 13
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Non-axially-symmetric structures
• Electrostatic Separators
Presentation title - 14
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Non-axially-symmetric structures
• Electrostatic Separators
Presentation title - 15
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Non-axially-symmetric structures
• Transverse kicks vs test charge position
Presentation title - 16
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CERN - IT DepartmentCH-1211 Genève 23
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Non-axially-symmetric structures
• Transverse kicks vs test charge position minus contribution of on-axis beam
Presentation title - 17
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Calculation of “Quadrupolar Wakes”
• Separating dipolar and quadrupolar wakes with Mafia/GdfidL ...
– Calculation with on-axis source charge to obtain “quadrupolar” wake component
– Calculation with displaced source charge distribution; substraction of “quadrupolar” component yields the “dipol”wake
Presentation title - 18
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Wakes in non-axially-symmetric structures• To describe a non-axially-symmetric
structure one needs typically 4 transverse wake tables
Presentation title - 19
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Thank you for your attention !
Questions ?