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THÈSE NO 8246 (2018)
PRÉSENTÉE LE 16 FÉVRIER 2018
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
Stefano BENEDETTI
acceptée sur proposition du jury:
Prof. R. Houdré, président du jury
Prof. L. Rivkin, Dr A. Grudiev, directeurs de thèse
Prof. A. Faus-Golfe, rapporteuse
Dr M. Dehler, rapporteur
Prof. G. Burt, rapporteur
Suisse
2018
Aimieigenitori
Acknowledgements
IwouldliketofirstthankmythesissupervisorDr.AlexejGrudievforhisconsistentsupport
duringtheseyears.HismostpreciousadvicethatIwilltakewithmeistostartasimulation
onlywhentheresultisalreadyknown,oratleastguessed.IfIwillreachonlyonehalfofhis
analyticalskillsIwillbesatisfiedbymyprofessionalcareer.
IamgratefultoProf.LeonidRivkinforhavingmeacceptedasPhDstudentandforthesupport
inparticipatingtotheCERNacceleratorschoolsinPragueandWien,andtotheJUASschool
inArchamps.
IamdeeplyindebtedtoProf.UgoAmaldi.Hefirstmotivatedandallowedmetoworkinthe
fieldofmedicalparticleaccelerators.IdidnotplantostartaPhDthesisinthisfield,buthis
enthusiasmpushedmeinthisdirection.Ifsomeonecanbecalled"guilty"forthisthesis,that
ishim.
ThankstoDr.AndreaLatina,whohasbeenhalfasupervisorandhalfacolleagueandafriend.
Iwillalwaysrememberhispatienceindrivingmethroughthesecretsofbeamdynamics.
ThankstoallmyTERAcolleaguesofthefirstgeneration:Valeria,Alessandra,Daniele,Caterina,
Fabrizio,Carlo,Mattia,Mohammad.AndinparticularthankstoAlberto,myfirstsupervisor,
andtoMartinaandGiovanni,fortheirpreciousadvicesandhelpinreviewingdocuments.
Fromaprofessionalpointofview,thosefirstyearsspentwithyouwasthehappiestperiodof
mythesis.
IamgratefultomyCERNcolleaguesDaniel,Anastasiya,Theo,BenandBenjaminfortheir
helpinsettingupandrunningthecavityexperiment. Thankstomyoffice-mateSamwho,
besidesalltheworksheputintheexperiment,boremeduringsomeverystressfullastmonths
ofwriting. AndIwouldliketothankDr. Igor. SyratchevandDr. WalterWuensch, whose
passiontowardsphysicsanimatedinapleasantwaymultipleCLICRFmeetingsandinspired
me.
ThankstotheTERAcolleaguesofthesecondgeneration,Mohammad,Pedroandinparticular
toVittorioandEnrico,whotookthenoteasytasktocarrythetorchofhadrontherapyresearch.
Mayitalwaysshine!
v
Acknowledgements
Lastbutnotleast,Iwishtoexpressmygratitudetomyfamily,whoprobablyabsorbedmostly
thelowmoments,andhelpedmethroughthem,withoutgettingtheniceperiods.ForthisI
amforemostthankful.
PlateaudesGlières,19Août2017
S.B.
vi
Abstract
Hadronbeams–approximately200MeVprotonsand400MeV/ufullystrippedcarbonions
–arebettersuitedtotreatdeep-seatedtumoursthanXraybeams–producedbyelectrons
acceleratedbylinearaccelerators(linacs)to5-25MeV–becausetheyleavethemaximum
energydensityattheendoftheirrangeinmatter,intheso-calledBraggpeak.Thisphysical
propertyallowsdosedepositionsthataremoreconformaltothetumourtargetandspare
muchbetterthesurroundinghealthytissues,sothathadrontherapytreatmentroomscould
substituteXraytherapyrooms(about20000worldwide)iftheneededacceleratorscouldbe
madeofsimilardimensionsandcosts.
Cyclotronsandsynchrotronsareattheheartoftodayprotonandcarboniontherapycentres,
respectively. Attheendof2015,morethan130000patientshavebeentreatedwithproton
beamsandalmost20000withcarbonions[ParticleTherapyCo-OperativeGroupdata,https:
//www.ptcog.ch/index.php/patient-statistics].Highfrequencyhadrontherapylinacshave
beenstudiedinthelast30years.Theirmainadvantageisrepresentedbytheiractivebeam
energymodulation,whichpermitsquicktreatmentswithsuperiorbeamqualityandnovel
dosedeliverytechniques.
Thisthesisisthelastofmanyresearchworksonthedevelopmentoflinearacceleratorsfor
hadrontherapy.Thepreliminarydesignoftwolinearacceleratorfacilities,forprotontherapy
(TULIP)andcarboniontherapy(CABOTO),wascompleted.Thisclosedanactivitythatstarted
wellbeforethebeginofthisPhD.
TheintroductoryChapterwillquicklyreviewtherationaleofhadrontherapyasatreatment
methodology,whichhasbeennicelycoveredinanumberofarticlesandthesisbefore.More
space will be dedicated to discuss the advantages of linacs in hadron therapy compared
tostate-of-arttechnologies, andtodiscussthedifferencesbetweencyclinac andall-linac
solutions. Finally, the most important past research activities based on which this thesis
startedwillbepresented.Thetheoryoflinearacceleratorsisnotpresented,sincemanybooks
coveritindetail.Instead,alongthedifferentChapters,shorttheoreticaldiscussionswillbe
givenwhenjudgednecessarytofullyexplainthechoicesmade.
ThesecondChapteristhelargestofthisthesis. ItdescribestheRFdesignofaccelerating
structuresperformedfortheprotonandcarboniontherapyfacilitieslateronpresented.The
vii
Abstract
firstcavitypresentedisa750MHzIHstructure,whichrepresentsanidealcontinuationofthe
recentlybuilt750MHzCERNRFQ.BothRFefficiencyandbeamdynamicsconsiderations
willbepresentedtoprovethisstatement. Forbeamenergieshigherthan10MeV/u,aside
coupledDTLcavitywasconsidered. Boththesetwoacceleratingstructuresrequireafairly
lowacceleratinggradient,andtheirdesignisincommonbetweenthetwoprojectsstudiedin
thisthesis. Finally,fortheprotontherapylinac,twohigh-gradientoptimizedcavitieswere
consideredforbeamenergiesabove70MeV.Abackwardtravellingwavecavity,magnetically
coupled, whichhasbeenbuiltandtested. Andasidecoupledcavity, whichhasbeen3D
RFdesignedbutnotbuilt. Forthecarboniontherapylinac, theRFefficiencyisthemost
importantparameter,andtheacceleratingstructurecouldnotbeoptimizedintermsofhigh
gradient. Thus,forthisproject,forenergieshigherthan100MeV/uahighefficiencyside
coupledcavitywasconsidered. Asdiscussedindetail,thisisafundamentallydifferentRF
designfromthehighgradientone.
Anotnegligibletimeofthepresentthesiswasdevotedtothedevelopmentofbeamdynamics
codes.Partially,thiswasmotivatedbythewilltobetterlearnbeamdynamics.However,the
linearacceleratorsstudiedhavesubstantialdifferencesbetweeneachother,andnonblack-box
toolspermittoaddfeaturesasnecessary,adaptingtothedesignneeds.Toeasethereading,
thediscussionofthesetoolshasbeenputintheAppendix.
AfterthesecondChapter,andideallytheAppendixonbeamdynamics,thereaderhasallthe
meanstofullycomprehendthefollowingChapters,wheretheprotonandcarbonionlinac
designsareeventuallypresented.
ThethirdChapterisdedicatedtotheprotonlinacdesign,calledTULIP:TUrningLInacfor
Protontherapy.TULIPmaincharacteristicisitscompactness,whichrequiredthestudyofthe
highgradientacceleratingstructurespreviouslydiscussed.TheChapterstartswithageneral
overviewofthelinaclayout,followedbythedetaileddescriptionofthebeamdynamicsstudies
performed.AnerrorstudyofquadrupolesmisalignmentcompletestheChapter.
TheforthChapterdescribesthecarbonionlinacdesign,calledCABOTO:CArbonBOosterfor
TherapyinOncology.ThisChapterfollowsthesameschemeoftheTULIPone.Inaddition,
givensomerecentinteresttowardsthistechnology,andgiventhesimilaritieswithcarbon
ionsfromalinacpointofview,apreliminarydesignofanHetherapyfacilityisdiscussed.The
Chapterisconcludedbyapreliminarycharacterizationofhadrontherapylinacscosts.
ThefifthChapterpresentstheexperimentalactivityperformedonthebackwardtravelling
waveprototypebuilt.Goalofthetestistostudythehigh-gradientbreak-downlimitationof
S-Bandcavities.SuchstudieswereconductedextensivelybyCLIC(CompactLinearCollider)
on 12 and 30 GHz accelerating structures. TERA Foundation, in collaboration with CLIC,
startedahighgradienttestonS-BandandC-BandstandingwavesingleRFcells.Thepresent
testprofitedoftheresultsoftheseexperiments,anditrepresentsthefirstattempttostudythe
highgradientlimitsofafullacceleratingstructureoperatingat3GHz.Afterthedescription
of the cavity RF tuning, the status of the test is presented, highlighting some interesting
viii
Abstract
peculiaritiesofthedesign.TheChapterisconcludedbythestudyofdarkcurrentcapturein
nonultra-relativisticcavities.
Keywords:hadrontherapy,linac,RFcavity,highgradienttest,beamdynamics,breakdown
rate
ix
Description:in participating to the CERN accelerator schools in Prague and Wien, and to Cyclotrons and synchrotrons are at the heart of today proton and carbon ion recent years research works and private companies focused their effort on However, hadron therapy linacs differ from every other application,.
