两个方向都未加反馈

BEPCIITransverseFeedbackSystemYueJunhuiIHEP，BeijingSep17th,08IMACIncludingthreeparts:ThemainparametersofBEPCIIThecoupledbunchinstabilityThebunchbybunchfeedbacksystem

OutlineI:SomeParametersofBEPCIIBeamEnergy,E

GeV

1.89Circumference,Cm

237.53Totalbeamcurrent,A

0.91Bunchcurrent,

mA

9.8Revolutionfrequency,MHz

1.2621RFfrequency,MHz

499.8HarmonicNumber,h

396Tunes,

6.57/7.61/0.034Radiationdampingtimes,ms

25/25/12.5NumberofBunches,B

93Bunchspacing,m

2.4Bunchfrequency,MHz

125

Thehighbeamcurrent(0.9A)andthelargenumberofbunches(93bunches)willcausethecoupledbunchinstabilities(CBI)inBEPCII

TwosourceThehigherordermodes(HOMs)ofRFcavitiesTheresistivewallimpedanceActivefeedbacksystemsarerequiredtosuppressCBIII:TheCoupledBunchInstability

BEPCIIwilloperateoncollidingmodeandsynchrotronmode.Soourtransversefeedbackwillhavethreesets:electronring,positronring,andsynchrotronring.Theelectronicsbandwidthshouldbeatleasthalfofthebunchfrequencycollidingmode62.5MHz

Synchrotronradiationmode250MHzThedesigndampingtimeoftransversefeedbacksystemis0.5msIII:BunchbybunchTransverseFeedbackSystemTransversefeedbacksystemlocatedinthestoragering

TheTransverseFeedbackSystem

SchematicdiagramFront-endelectronicsSignalprocessingsystemKickerandpoweramplifierParametersofTransverseFeedbackSystemTheexperimentsofBEPCIITFBTheSchematicDiagramofTFBSystemThelocalstationoftheTransverseFeedbackSystem

Transferthesignalwhosebandwidthis500MHzatthecenterfrequencyof1.5GHztobaseband.Detectionfrequencyis1.5GHz，tripleofRFThelocalDCrejectioncircuitinfixed-voltagemode

Front-endelectronics

Signalprocessingsystem

FullanalogsystemsimplyusingthecablelineThreefunctionsMakingthe90phaseshiftRejectiontheclosedorbitsignalOneturndelayRealizationTwomanualattenuatorsfor90phaseshiftcontrolNotchfilterrejectiontherevolutionfrequencyThetimedelaybycableSignalprocessingsystem–

PhaseshiftandNotchFilter

KickerandPowerAmplifier

Fourstriplineelectrodeaskicker(consideringitiseasytorealize,sothekickerlengthis600mmjustforeveryotherbunches)OnekickerperringbecausethelimitedspaceModel75A250Apoweramplifierisselected.Two75A250Aareconnectedinthedifferentialstyle

KickerandPowerAmplifierSpecificationsoftheTFBsystem

RFfrequency

MHz

499.8Bunchspacingns

8Feedbackdampingtime

ms

0.5Detectionfrequency

GHz

1.5Numberofkickersperplaneperring

1Kickershuntimpedance(at125MHz)kW

4.0Totaldampingvoltageperturn

V

800Kickerpowerfor800Vw

106Numberofpoweramplifiersperplaneperring

2BandwidthofpoweramplifierMHz

250BeamprofileswithTFBturningoffandon

两个方向都未加反馈两个方向都加只加y方向只加x方向TFBoffTFBonSidebandssuppressedbyTFBsystemTransverseinstabilitiesinfullbandwidthof125MHzsuppressedbyTFBsystemwithbeamcurrent243mAwith99bunchesinpositronring.Thebackgroundfrequencylinesarerevolutionfrequencyharmonicsandthedark-colouredlinesareinstabilitysidebands.Wecanseethatthemagnitudeofinstabilitysidebandsisattenuatedmorethan30dBwhenthefeedbackison.

TFBoffTFBonMeasurementofdampingtimeofTFBFBOFFFBONSinglebunch3mA；Dampingtimeis2.43mswithTFBoff;Dampingtimeis0.4mswithTFBonSotao_FB＝2.43*0.4/(2.43-0.4)=0.4788ms.MeasurementofdampingtimeofTFB(cont’)SummaryThetransversefeedbacksystemsofBEPCIIhavebeeninstalledandplayedanimportantroleduringthecommissioningofBEPCIIdoublerings.Itcansuppressthestrongmulti-bunchinstabilitiesatthehigherbeamcurrentofover500mA.Inthenextstage,weneedcarefultuningthesystemandmakesureofsuppressingthetransverseinstabilitiesathighercurrent.Inaddition,remotecontrolan