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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severalsynchrotronradiationmonitors:asthebeamisbentindipolemagnets,itemits components<strong>and</strong>potentiallydamageselectronicssystem. synchrotronradiation.IntheIRFELthisradiationisemittedintheinfra-redregionofthe wirecanyieldsalargelossofparticlethatcanhitthevacuumchamberorotherbeamline<br />
manytransitionradiationmonitors:thinaluminumfoilareinsertedintothebeampath electromagneticspectrum<strong>and</strong>isimagedonaverysensitiveCCDdetector(seeg.4.1c).This prolemonitorhastheadvantageofbeingnon-invasive(itdoesnotyieldbeamdegradation) <strong>and</strong>itcanbeusedtomeasurebeamdistributionatveryhighcurrent.Howeveritisnotwell<br />
radiationisdetected(seegure4.1d).Thiscongurationrequiresthefoilmaterialtohave <strong>and</strong>transitionradiation(seetheIntroductionchapter)isdetectedwithaCCDdetector. Generallythefoilmakesa45deganglewiththebeamdirection<strong>and</strong>backwardtransition suitedforemittancemeasurement:thebeamproleismeasuredinabendi.e.atadispersive<br />
agoodreectioncoecient.Sinceverythinfoilareavailable,thistypeofdevicescanst<strong>and</strong> location<strong>and</strong>thereforetheemittancecomputation,requiresasomewhattediousanalysissince<br />
highcurrentbeamwithoutyieldingsignicantbeamdegradation. weneedtodeconvolvedthedispersioncontributiontothebeamprole.<br />
Suchstudies,experimentallycarriedintheCEBAFmachineatJeersonLab,helpedwiththechoice ofthetypeofscreen(aluminum).Duringthesestudieswealsodevelopedaquasinon-interceptive screenthatwasusedtomeasurethebeamproleofthehighpowerbeamoftheCEBAFaccelerator; choicewasprincipallydrivenbythereliability,thespeed<strong>and</strong>thelowcostofthistypeofinstrument. BeforetheIRFELwasbuiltwestudymanyaspectofthistypeofapparatus:whataretheaverage beamcurrentlimit,whatarethebeamtransversephasespacedegradationafteranOTRscreen. measurementoftransversedistributionrequiredformeasuringtheemittanceintheIRFEL.This Amongthetechniqueslistedabove,transitionradiationwaschosentoprovidethequantitative<br />
alsowedidnotimplementthistypeofmonitorintheIRFELshorttermplan,itmightbesometime implementedtocontinuouslymonitortheelectronbeamqualitywithoutsignicantimpacton<br />
AswehavementionedinChapter2,whenwediscussedelectromagneticradiationemittedbymoving diagnostics<strong>and</strong>thedevelopmentofthenoninterceptiveprolemonitor. 4.2.1ThelimitationofTransitionRadiationMonitor thebeamitself.Inthefollowingsectionswediscussthelimitationsoftransitionradiation-based<br />
methodallowstheobservationoftheTRproducedasthebeamcrossestheboundaryvacuum/foil (backwardTR)orfoil/vacuum(forwardTR).Asthebeamisinterceptedbythefoilsomeconcerns mightarise: FirstlybecauseofthedE=dxofthematerialthebeamdepositssomeenergyintheTRradiator therebyincreasingitstemperature.Thereforewemuststudythethermaleectofthebeamonthe chargedparticles,thattransitionradiationcanbeobservedwheneverachargedparticleexperience<br />
TRradiator. adiscontinuityintheelectricpropertiesofitsenvironment.Acommonwayofobservingtransition<br />
Secondlywhentheelectronsthatconstitutethebeampassthroughthefoilmaterial,theyundergo radiationistointerceptthebeamtrajectorywithathinmetallicfoil(orTRradiator).Such<br />
resultinanon-interceptivediagnostics.Ontheotherh<strong>and</strong>,thedivergenceinducedviascattering<br />
scatteringonthenucleithatcanpotentiallydegradesthebeamemittance<strong>and</strong>thereforewillnot
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