Cavity BPM Simulations A. Liapine

Analysis of the Existing BPMs BINP KEK

Analysis of the Existing BPMs BPM R/Q, Ohm at 1mm β (coupling factor) Q ext τ, ns (decay time) BINPSimulation NA0.35*25000*317* Diode KEKSimulation NA Diode ATF2 plans *Q 0 =8600 used for calculation, elsewhere Q 0 =8180

KEK BPM Issues  Usual way of simulation: cavity and wg-to-coax adapter are simulated separately to reduce the total computation time and memory consumption  Suggestion (M.Ross): simulate the whole geometry as well for a better understanding  Results are different! – Coax adapter geometry is important… Coupling coefficient Q ext Decay time waveguide only separate adapter whole structure diode measurement NA measurement

KEK BPM Issues  Structure is not symmetric, some monopole leakage is possible  Q ext is huge, therefore estimating the amplitudes for a unit of the stored energy, then normalizing with shunt impedances A 010 =5.65 V/m A 110 =1250 V/m R/Q 010 =114 Ohm R/Q 110 =1.26 Ohm Introducing asymmetries: Slot + wg + feedthrough shifted by 0.5 mm: 73 μm Slot shifted by 0.5 mm: 73 μm Feedthrough shifted by 0.5 mm: 63 μm

 Successor of previous designs  “Longitudinal” design  4-coupler symmetrical structure  Beam pipe diameter increased to 20 mm to meet the ATF2 beam optics requirements  Increased coupling for a higher sensitivity Q ext =13000  Dipole mode frequency 6426 MHz Monopole leakage: Total waveguide length 20 mm – 500 nm 30 mm or more – leakage is less than computation error Introducing asymmetries (Slot + wg + feedthrough shifted by 0.5 mm, 0.25 mm meshstep) Total waveguide length 30 mm – 40 μm 40 mm – 20 μm 50 mm – 12 μm Check with 0.2 mm meshstep: Check with 0.2 mm meshstep : 50 mm – 10 μm ATF2 Design Incline component estimation: 7 μm/mrad

Dimension Refl. growth Accuracy ff position < 0.05/100 μm ±50μm pin length 0.05/100 μm ±20μm ins. radius 0.05/100 μm ±20μm ins. height < 0.05/100 μm ±50μm Bandwidth: 1500 MHz ATF2 Design