Cavity BPM Cavity BPM SimulationsSimulations

A. LiapineA. Liapine

Analysis of the Existing BPMsAnalysis of the Existing BPMs

BIN

PK

EK

Analysis of the Existing BPMsAnalysis of the Existing BPMs

BPMBPM R/Q, R/Q, Ohm at Ohm at 1mm1mm

ββ (coupling (coupling factor)factor)

QQextext ττ, ns , ns (decay (decay time)time)

BINPBINP SimulationSimulation 0.800.80 0.310.31 2635026350 304304

NANA 0.35*0.35* 25000*25000* 317*317*

DiodeDiode 0.870.87 94009400 216216

KEKKEK SimulationSimulation 0.900.90 0.170.17 4702047020 338338

NANA 0.10.1 8180081800 361361

DiodeDiode 0.250.25 3212032120 317317

ATF2 plansATF2 plans 0.60.6 1360013600 248248

*Q0=8600 used for calculation, elsewhere Q0=8180

KEK BPM IssuesKEK BPM Issues Usual way of simulation: cavity and wg-to-coax adapter are Usual way of simulation: cavity and wg-to-coax adapter are

simulated separately to reduce the total computation time simulated separately to reduce the total computation time and memory consumptionand memory consumption

Suggestion (M.Ross): simulate the whole geometry as well for Suggestion (M.Ross): simulate the whole geometry as well for a better understandinga better understanding

Results are different! – Coax adapter geometry is important…Results are different! – Coax adapter geometry is important…

Coupling Coupling coefficiencoefficien

tt

QQextext Decay Decay timetime

waveguide onlywaveguide only

separate adapterseparate adapter

whole structurewhole structure

0.480.48

0.340.34

0.170.17

1699016990

2427024270

4702047020

268268

298298

338338

diode diode measurementmeasurement

NA measurementNA measurement

0.250.25

0.10.13212032120

8180081800317317

361361

KEK BPM IssuesKEK BPM Issues Structure is not symmetric, Structure is not symmetric,

some monopole leakage is some monopole leakage is possiblepossible

QQextext is huge, therefore is huge, therefore estimating the amplitudes for a estimating the amplitudes for a unit of the stored energy, then unit of the stored energy, then normalizing with shunt normalizing with shunt impedancesimpedancesA010=5.65 V/mA110=1250 V/mR/Q010=114 OhmR/Q110=1.26 Ohm

Introducing asymmetries:Introducing asymmetries:Slot + wg + feedthrough shifted by 0.5 mm: 73 Slot + wg + feedthrough shifted by 0.5 mm: 73 μμmmSlot shifted by 0.5 mm: 73 Slot shifted by 0.5 mm: 73 μμmmFeedthrough shifted by 0.5 mm: 63 Feedthrough shifted by 0.5 mm: 63 μμmm

Successor of previous designsSuccessor of previous designs “ “Longitudinal” designLongitudinal” design 4-coupler symmetrical structure4-coupler symmetrical structure Beam pipe diameter increased to Beam pipe diameter increased to 20 mm to meet the ATF2 beam 20 mm to meet the ATF2 beam optics requirementsoptics requirements Increased coupling for a higher Increased coupling for a higher sensitivity Qsensitivity Qextext=13000=13000 Dipole mode frequency 6426 MHzDipole mode frequency 6426 MHz

Monopole leakage:Monopole leakage:Total waveguide length 20 mm – Total waveguide length 20 mm – 500 nm500 nm30 mm or more – leakage is less 30 mm or more – leakage is less thanthancomputation errorcomputation errorIntroducing asymmetriesIntroducing asymmetries (Slot + wg (Slot + wg + + feedthrough shifted by 0.5 mm, 0.25 feedthrough shifted by 0.5 mm, 0.25 mm meshstep)mm meshstep)Total waveguide length 30 mm – 40 Total waveguide length 30 mm – 40 μμmm40 mm – 20 40 mm – 20 μμmm50 mm – 12 50 mm – 12 μμmmCheck with 0.2 mm meshstepCheck with 0.2 mm meshstep ::50 mm – 10 50 mm – 10 μμmm

ATF2 DesignATF2 Design

Incline component estimation: Incline component estimation: 7 7 μμm/mrad m/mrad

DimensionDimension Refl. growthRefl. growth AccuracAccuracyy

ff positionff position < 0.05/100 < 0.05/100 μμmm

±±5050μμmm

pin lengthpin length 0.05/100 0.05/100 μμmm ±±2020μμmm

ins. radiusins. radius 0.05/100 0.05/100 μμmm ±±2020μμmm

ins. heightins. height < 0.05/100 < 0.05/100 μμmm

±±5050μμmm

Bandwidth: 1500 MHzBandwidth: 1500 MHz

ATF2 DesignATF2 Design