Electromagnetic Simulation of CERN Accelerator Components and Experimental Applications

181 Pages·2013·9.25 MB·English

by  Zannini, Carlo

Electromagnetic Simulation of CERN Accelerator
Components and Experimental Applications
THÈSE NO 5737 (2013)
PRÉSENTÉE LE 18 jUIN 2013
À LA FACULTÉ DES SCIENCES DE BASE
LABORATOIRE DE PHYSIQUE DES ACCÉLÉRATEURS DE PARTICULES
PROGRAMME DOCTORAL EN PHYSIQUE
ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE
POUR L'OBTENTION DU GRADE DE DOCTEUR ÈS SCIENCES
PAR
Carlo ZANNINI
acceptée sur proposition du jury:
Prof. V. Savona, président du jury
Prof. L. Rivkin, Dr G. Rumolo, directeurs de thèse
Dr M. Barnes, rapporteur
Dr M. T. Tran, rapporteur
Prof. U. van Rienen, rapporteur
Suisse
2013

Contents
Acknowledgments v
Abstract vii
Sintesi ix
Introduction 1
1 WakefieldsandImpedance 5
1.1 Theelectromagneticproblem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.1 Longitudinalplane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.2 Transverseplanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.1.3 Effectonthebeamdynamics . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2 EMsimulationsofwakefieldsandimpedances . . . . . . . . . . . . . . . . . . . 14
1.2.1 CSTStudioSuite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2.2 Resistivewall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.2.3 PillboxCavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.2.4 Step-inandstep-out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2 Impedancemodelofferritekickers 41
2.1 SimplemodelofSPSferriteloadedkickers . . . . . . . . . . . . . . . . . . . . . . 41
2.1.1 TheoreticaltransverseimpedanceoftheSPSkickers . . . . . . . . . . . . 41
2.1.2 EMsimulationsofSPSkickers . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.2 ASpectralMethodforImpedanceCalculation . . . . . . . . . . . . . . . . . . . . 55
2.2.1 C-Magnetmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.2.2 AsimplifiedC-Magnetmodelforimpedancecalculations . . . . . . . . . 56
2.3 EffectoftheTEMmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
2.3.1 Theoreticalmodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
2.3.2 ComparisonWith3-DSimulations. . . . . . . . . . . . . . . . . . . . . . . 71
2.3.3 Effectoftheexternalcircuits . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.4 RealisticmodelofSPSkickers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
2.4.1 Effectofthelongitudinalsegmentation . . . . . . . . . . . . . . . . . . . . 74
2.4.2 SPSextractionkicker:effectoftheserigraphy . . . . . . . . . . . . . . . . 75
2.4.3 Simulationofakickerloadedbyacoaxialcable . . . . . . . . . . . . . . . 79
iii
Contents
2.4.4 SPSkickerimpedancemodel . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3 Resistivewallimpedancecalculations 85
3.1 ATLmodelforwallimpedancecalculation . . . . . . . . . . . . . . . . . . . . . . 85
3.1.1 Descriptionofthemodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
3.1.2 BenchmarkwithReWall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
3.1.3 ApplicationtotheSPSwallimpedancemodel . . . . . . . . . . . . . . . . 92
3.2 ImpedanceoftheLHCbeam-screen . . . . . . . . . . . . . . . . . . . . . . . . . . 95
3.2.1 Thescalingtechnique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.2.2 ElectromagneticsimulationoftheLHCbeam-screenincludingtheweld 97
4 Experimentalapplications 101
4.1 Benchmeasurements:thewiremethod . . . . . . . . . . . . . . . . . . . . . . . . 101
4.1.1 Numericalinvestigationofthewiremethod . . . . . . . . . . . . . . . . . 102
4.1.2 Comparingwiremeasurementsandimpedancemodels . . . . . . . . . . 103
4.2 Observationswithbeam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.2.1 Tuneshiftsmeasurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.2.2 MKEheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.3 EMcharacterizationofmaterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.3.1 Methodsformeasuringthematerialproperties . . . . . . . . . . . . . . . 126
4.3.2 TheCoaxiallinemethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4.3.3 Airgap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.3.4 Measurementresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Conclusions 137
A EMsimulationsofCLICcomponents 141
A.1 EMsimulationsofCLICcrabcavities . . . . . . . . . . . . . . . . . . . . . . . . . 141
A.1.1 Introductionandmotivation . . . . . . . . . . . . . . . . . . . . . . . . . . 141
A.1.2 CST3DEMsimulationstudies . . . . . . . . . . . . . . . . . . . . . . . . . 142
B Spectralmodelforthecalculationofthetransverseimpedanceofanabrupttransi-
tion 147
B.1 Theanalyticalapproach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
B.1.1 ProjectionofMaxwellequationinr andϕ . . . . . . . . . . . . . . . . . . 148
B.1.2 Fieldmatching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
B.2 Impedancederivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
B.2.1 Numericalresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
C Calculationofζ :transmissionlinemodel 153
m
D ListofPublications 155
CurriculumVitae 171
iv
Acknowledgments
IamveryproudtohaveworkedunderthesupervisionofGiovanniRumolo.ImetGiovanniin
November2008whenIstartedmyexperienceatCERNasTechnicalStudent.Iimmediately
appreciatedhisknowledgeandskill. Heguidedme,andwasalwaysopentomyinitiatives.
GiovanniRumolowentwellbeyondhisdutyofthesisco-director:hehasbeenamentoranda
friend,alwayssuggestingtomethebestformyresearchafterexaminingmyworkwithcritical
lookdaybyday.
AspecialthankstomythesisdirectorLeonidRivkin,whogavemetheuniqueopportunityto
joinEPFLasaDoctoralStudent.Inaddition,inspiteofthedistanceandhistimeconstraints,
heprovidedmewithhelpandsupportonnumerousoccasions.
IamalsoverygratefultoGianluigiArduiniandEliasMétral,mysectionleadersduringthe
phDresearch.EliasandGianluigialwayssupportedmyinitiatives.
IwouldliketothankProf.VittorioVaccaroforthecontinuouscooperationandexchangethat
wehadduringthesethreeyearsofresearch.Furthermore,IcannotforgetthatProf.Vaccaro
togetherwithIaiaMasullointroducedmetothefascinatingfieldofacceleratorphysics.
Thankstomanycolleaguesforusefuldiscussionsandfruitfulcollaborations. Inparticular
Iwouldliketothank: MikeBarnes,HannesBartosik,NicolòBiancacci,RamaCalaga,Fritz
Caspers,HugoDay,AlessandroD’Elia,AlexejGrudiev,GiovanniIadarola,EliasMétral,Andrea
Mostacci,NicolasMounet,RaphaelMutzner,TatianaPieloni,BenoitSalvant,BrunoSpataro,
MauroTaborelli,RiccardoZennaro.
AspecialthankstoGiovanniDeMichelefortheclosecollaborationonRFmeasurements.
ManythankstotheRFcolleaguesTheodorousArgyropoulos,ThomasBohlandElenaSha-
poshnikova.Thanks,toMirandaVanStenisandThomasSchneiderforthemachiningofthe
coaxialsamplesformeasurementsofmaterialpropertiesandtoSergeLebetfortechnical
assistance.
ThankstotheunofficialCERNitalianteamthatnevermademefeelalone:FedericoAglietti,
StefanoCengarle,AlessandroDanisi,SalvatoreDanzeca,IvanDeCesaris,GiovanniDeMichele,
GiovanniIadarola,CinziaLuzzi,MicheleMartino,GiovanniSpiezia.
ThankstoTatianaLiberaRijoffforsupportingmeinthedailylifeduringthewritingupofthe
thesisandfortheLATEXsupport.
Infineungrazieparticolareallamiafamigliaaimiefratellieaimieigenitori;questatesila
dedicoaloro.
v

Abstract
Wakesandimpedancesofsingleacceleratorelementscanbeobtainedbymeansoftheoretical
calculation,electromagnetic(EM)simulationsorbenchmeasurements. Sincetheoretical
calculationsapplyonlytosimplestructuresandbenchmeasurementshavesomeintrinsic
limitations,EMsimulationscanbeusedasareliabletooltodeterminewakesandimpedances.
Thisthesiswillfocusontheuseoftimedomain3DCSTParticleStudioEMsimulationsto
calculatewakesand/orimpedances.
First,theresultsoftheEMsimulationsarecomparedwiththeknownanalyticalsolutionsand
othercodes.Inthisexercise,thedrivingandthedetuningtermsofthewakes/impedances,in
thetransverseplane,aredisentangledforbothsymmetricandasymmetricgeometries.The
sensitivityofthesimulationsresultstothenumericalparametersisdiscussed,aswellasthe
limitsofvalidityofthewakeformalismanditsextensiontothenonlinearregime.
UsingtheCSTWakefieldSolver,theSPSkickerimpedancecontributionisthenestimated.The
simulationmodelwasimprovedstepbystep,andsuccessfullybenchmarkedwithexisting
andnewtheoreticalmodels,givingconfidenceinthenumericalresultsandallowingabetter
understandingoftheEMproblems.
Inthecaseoftheresistivewallimpedanceofsimplechambergeometriesahandytheoretical
modelhasbeenproposed.Inordertocalculatetheresistivewallimpedanceofaroundcham-
ber,atheoreticalapproachbasedonthetransmissionline(TL)theory,isdemonstratedtobe
validandpracticaltouse.Bymeansofappropriateformfactorsthemethodisthenextended
torectangularorellipticalchambers.
Moreoverthemethodwassuccessfullybenchmarkedwiththemostrecentcodesbasedon
the field matching technique developed at CERN and was used to construct the SPS wall
impedancemodel.Formorecomplicatedgeometries(asymmetries,smallinserts,holesetc.),
atheoreticalestimationwithoutinvolvingEMsimulationbecomesunworkable.Anexample
ofinterestistheLHCbeam-screen,forwhichCST3Dsimulationswereusedtoestimatethe
impedance.Inordertoallowthesimulatortocoverthewholefrequencyrangeofinterest(few
KHztoseveraltensofMHz)anovelscalingtechniquewasdevelopedandapplied.
Wherepossible,theEMmodelsdevelopedthroughoutthisthesiswerealsosuccessfullybench-
marked with bench measurements (wire methods) and observations with beam. On the
specificsubjectofbenchmeasurements,anumericalinvestigationofcoaxialwiremeasure-
mentshasbeenalsopresented.
Finally,inordertoverifytheadoptedEMmodelsofthematerialsbothintheoreticalcalcula-
tionsand3Dsimulations,anexperimentalsetupformeasuringEMproperties(permittivity
vii
Abstract
andpermeability)ofmaterialshasbeenpresented.Themethodisbasedonfittingthemea-
suredreflectiontransmissioncoefficientsthroughacoaxiallinefilledwiththematerialtobe
probed,withtheoutcomeofEMsimulationsortheoreticalmodels.Itwassuccessfullyapplied
formeasuringNiZnferritesanddielectricmaterial(e.g.SiC).
Keywords:accelerator,collectiveeffects,wakefunctions,impedance,CSTParticleStudio,EM
simulations,kickers,resistivewall,SPS,LHC,impedancemeasurements,coaxialwire,tune
shift,powerloss,beaminducedheating,materialsproperties,complexpermittivity,complex
permeability.
viii
Sintesi
Funzionisciaeimpedenzediaccoppiamentodeglielementidiunacceleratorepossonoes-
sereottenutetramitecalcoliteorici,simulazionielettromagnetiche(EM)omisuredabanco.
Tuttavia,datocheicalcoliteoricisonodisponibilisoloperstrutturesempliciechelemisure
dabancohannoalcunelimitazioniintrinseche,lesimulazioniEMpossonoessereusatecome
unostrumentoaffidabileperdeterminarecampisciaeimpedenzediaccoppiamento.Questa
tesisiconcentrasull’utilizzodisimulazioniEM3Dneldominiodeltempoperilcalcolodi
campisciaeimpedenzediaccoppiamento,realizzatecon’CSTParticleStudio’.
Comeprimopasso,irisultatidellesimulazioniEMsonoconfrontaticonsoluzionianalitichee
altricodici.Inquestoesercizioiterminidipolareequadrupolaredellefunzionisciaoequiv-
alentementedelleimpedenzediaccoppiamento,nelpianotransverso,sonostatiseparati
siaperstrutturesimmetrichecheasimmetriche.Lasensibilitàdeirisultatidellesimulazioni
rispettoaiparametrinumericivienediscussa,cosiccomeilimitidivaliditàdelformalismo
dellefunzionisciaelasuaestensionealregimenonlineare.
Usandoilrisolutoredicampisciadi’CSTParticleStudio’,èstatastimatal’impedenzadiac-
coppiamentodeikickerdiSPS.Ilmodellodisimulazioneèstatomiglioratopassodopopasso
everificatoconesistentienuovimodelliteorici,conferendoaffidabilitàairisultatinumericie
permettendounamigliorecomprensionedelproblema.
Nelcasodell’impedenzadelleparetiresistivedellecameredavuotodell’acceleratore,per
semplicigeometriedellacamera,vienepropostounsemplicemodelloteorico.Talemodello,
basatosullateoriadellelineeditransmissione(TL)permettedicalcolarel’impedenzadelle
paretiresistivepercamereasezionecircolareedèstatodimostratoesserevalidoefacileda
usare.Mediantel’usodifattoridiformailmetodopuòessereapplicatoacamererettangolari
oellittiche.
InoltreilmetodoèstatoconfrontatoconicodicipiùrecentisviluppatialCERNedèstato
usatopercostruireilmodellod’impedenzadelleparetidiSPS.Pergeometriepiùcomplicate
(asimmetrie,piccoliinserti,pareticonforietc.),unastimateoricadell’impedenzasenzal’uso
disimulazioniEMdiventaimpraticabile.Unesempiodiinteresse,inquestosenso,èil’beam
screen’diLHCdovesimulazioni3DCSTsonostateusatepervalutarel’impedenza.Inmodo
tale da consentire al simulatore di coprire l’intero intervallo di frequenze di interesse (da
alcunikHZadecinediMHz)èstatasviluppata,verificataperuncasosempliceedapplicata
unanuovatecnicadiscalaturainfrequenza.
Ilmodelloèrisultatoinbuonaccordoconlemisuredabanco(metodidelfilo)eosservazioni
effettuateconilfasciodiparticelle.Sulsoggettospecificodimisuredabanco,èstatapresen-
ix
Sintesi
tataun’investigazionenumericadellemisureconilfilo.
Infine,alloscopodiverificareimodelliadottatiperleproprietàEMdeimateriali,siaperi
calcoliteoricicheperlesimulazioni3D,èstatopresentatounsetupsperimentalepermisurare
leproprietàEM(permeabilitàmagneticaepermittivitàelettrica)deglistessi. Ilmetodosi
basasullaconvergenzatraicoefficientiditransmissioneoriflessionemisuratisuunalinea
coassialeriempitaconilmaterialedacaratterizzare,eirisultatidisimulazioniEMomodelli
teorici.QuestometodoèstatoapplicatoconsuccessopermisurareleproprietàEMdiferriti
NiZnematerialidielettrici(p.es.SiC).
Keywords:acceleratore,effetticollettivi,funzioniscia,impedenza,CSTParticleStudio,sim-
ulazioniEM,calciatori,paretiresistive,SPS,LHC,misurediimpedenza,filocoassiale,tune
shift,perditadipotenza,riscaldamentoindottodalfascio,proprietàdeimateriali,permittività
complessa,permeabilitàcomplessa.
x