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On rf-finger heating and trapped mode damping in LHC collimator

On rf-finger heating and trapped mode damping in LHC collimator. Alexej Grudiev CWG meeting 14.02.05. Distribution of rf-losses on the rf-fingers due to longitudinal mode at 1.247 GHz. [a.u.]. rf-finger #8. rf-finger #4. rf-finger #1. Losses in CuBe and Ag-coated rf-fingers.

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On rf-finger heating and trapped mode damping in LHC collimator

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  1. On rf-finger heating and trapped mode damping in LHC collimator Alexej Grudiev CWG meeting 14.02.05

  2. Distribution of rf-losses on the rf-fingers due to longitudinal mode at 1.247 GHz [a.u.] rf-finger #8 rf-finger #4 rf-finger #1

  3. Losses in CuBe and Ag-coated rf-fingers Ag-coating is 5μm thick what is “much” bigger than skin-depth in Ag at 1.247 GHz which is 2μm

  4. Effect of rf-finger sliding contact resistance A-A Stainless steel Surface impedance of a good conductor: Zs = (1+i)/σδ Resistance of a stripe of size L x d: R = Re{Zs} L/d at 1.25 GHz Rss = 1/(106·15·10-6)·150/(50·sin6o ) = 2 Ω RAg = 1/(6·107·2·10-6)·150/3 = 8 mΩ Rc < 7.5 mΩ 150 Rc Ag-coated 3 50 A-A 6o Contact resistance Rc is mach smaller than the equivalent surface resistance (Rss+RAg)/2

  5. Damping of transition modes 4S60 ring 3x3 mm at 1.2 GHz ε = 12 + i7 μ = 1.6 + i9 SiC ring 11x6 mm at 2 GHz ε = 15; tanδ = 0.5 μ = 1 Parameters of the dangerous mode

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