Cavity BPM Simulations

1. Cavity BPM Simulations A. Liapine

2. Analysis of the Existing BPMs BINP KEK

3. Analysis of the Existing BPMs *Q0=8600 used for calculation, elsewhere Q0=8180

4. 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…

5. KEK BPM Issues • Structure is not symmetric, some monopole leakage is possible • Qext is huge, therefore estimating the amplitudes for a unit of the stored energy, then normalizing with shunt impedances A010=5.65 V/m A110=1250 V/m R/Q010=114 Ohm R/Q110=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

6. ATF2 Design • 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 Qext=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: 50 mm – 10 μm Incline component estimation: 7 μm/mrad

7. ATF2 Design Bandwidth: 1500 MHz