High Brightness Electron Beam Diagnostics and their ... - CASA
High Brightness Electron Beam Diagnostics and their ... - CASA
High Brightness Electron Beam Diagnostics and their ... - CASA
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B.3.3PARMELA FeaturesofJeersonLabVersion \Phase<strong>and</strong>RadialMotionin<strong>Electron</strong>LinearAccelerators."Itisaversatilemulti-particlecode thattransformsthebeam,representedbyacollectionofmacroparticles,throughauser-specied linac<strong>and</strong>/ortransportsystem.Itincludesa2-Dspace-chargecalculation<strong>and</strong>anoptional3-D point-to-pointspace-chargecalculation.PARMELAintegratestheparticletrajectoriesthrough theelds.Thisapproachisespeciallyimportantforelectronswheresomeoftheapproximations nothold.PARMELAworksequallywellforeitherelectronsorions.PARMELAcanreadeld usedbyothercodes(e.g.the"drift-kick"methodcommonlyusedforlow-energyprotons)would<br />
AtJeersonLab,amodiedversionofparmelahasbeenproducedbyH.Liu.Itincorporatesa3D distributionsgeneratedbyeitherFISHforrfproblemsorPOISSONformagnetproblems. ModiedSpacechargealgorithm point-by-pointspacechargealgorithmfromK.T.Mc.Donald4.Anoutlineofthealgorithmisas follows.parmelauseatwo-stepmethodtogenerateaspacechargeimpulseoneachmacroparticle: (!)itdeterminesthenetelectromagneticspacechargeeldatthelocationofeachmacroparticle duetoallothermacroparticle,(2)applythespacechargeimpulsetoeachmacroparticle.Then trackthemacroparticlethroughaslice(widthdenedbytheuser)ofthebeamline(forsimple elementthetrackingisperformedusingsecondordertransfermatrix,buttheusercanifdesired eachslice).Thisspacepoint-by-pointalgorithmisverysimplebutbecauseofthe1=r2dependence denethe3Dmapoftheelectromagneticeld.Insuchcasetheequationofmotionisintegratedin (whichcanleadtosingularityornumericalnoise)itmustbeimplementedcarefully.Forinstancein theeventualitytwomacroparticlescomeveryclosetoeachotherthechargeofthemacroparticles inthealgorithmisreduced.Thealgorithmtoreducethemacroparticlechargeisdiscussedindetail elsewhere5 AsimplemodelforCoherentSynchrotronRadiation chargeQi<strong>and</strong>lengthiorbitingonacirculartrajectoryofradiusRidetectedatthepresenttime byanobserverelectronjderived<strong>and</strong>expressedas: TheimplementationoftheCSRinteractionintothePARMELAcodecloselyfollowsthemethod describedbyCarlsten6wheretheelectriceldgeneratedataretardedangle0byalineiofuniform<br />
forshortelectronbunchesincircularmotionusingtheretardedGreen'sfunctiontechnique"Phys.RevE54num1, TN-94-040,JeersonLab,NewportNews,VA-USA(1994) pp838-845(1996)<br />
4K.T.McDonald,IEEETrans.Elect.Dev.35p2052(1988) 6B.E.Carlsten,\Calculationofthenoninertialspace-chargeforce<strong>and</strong>thecoherentsynchrotronradiationforce 5H.Liu,\ConceptofVariableParticleSizeFactorforaPoint-by-PointSpaceChargeAlgorithm",CEBAFreport Ei;j=Qi i"1 r(1!ibnij)"12i2ixj Ri+2i(1cos(0))##fr (B.9)