Download - Update on impedance of enamel flanges in SPS
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Update on impedance of enamel flanges in SPS
B. Salvant and V. Vaccarofor the ICE impedance team
12/05/2011
Many thanks to E. Shaposhnikova and M. Jimenez
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Context• 2 flanges coated by a small layer of isolating material
(enamel+vetronite) at each side of each BPM.
• Geometry is not trivial and small layers are hard to simulate with 3D codes
• Theory of impedance of inserts has been recently implemented by Shobuda et al (HB2010).
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geometry
Many warnings in CST due to mesh cells filled with PEC
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Simpler geometry for a hexahedral mesh square flange
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Comparison between square and round (real longitudinal)
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Low frequency peak?
• More details in the talk with V. Vaccaro tomorrow at the impedance meeting
With longer bunch: wake looks like the charge and discharge of a capacitor: physical?
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First tests indicate that peak at low frequency is proportional to the capacitance of the insert
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Transverse impedance (for 5 mm displacement)
Z(low freq)~ 0.3/0.005*436 ~26 kOhm/m
For all 436 flanges.Not accounting for the beta functions
Peaks at about 200 MHz
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Summary• Difficult simulations, should be crosschecked with ABCI and
Shobuda’s formula.• What isolation is really in the machine (thickness? EM properties?
Ageing?)
However:• Small transverse single bunch effects expected (as bunch length is
small). • Longitudinal effects and resonances at ~200 MHz to be followed
up.• These isolating inserts should be much more detrimental to
machines with longer bunches
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