低能离子束横向发射度的测量及分析

低能离子束横向发射度的测量及分析

31 2007 7

HIGH

ENERGY

PHYSICS

AND

NUCLEAR

PHYSICS

Vol.31,Supp.

Jul.,2007

MeasuringandAnalyzingTransverseLow-Energy

IonBeamEmittances*

M.P.Stockli1)

(SpallationNeutronSource*,OakRidgeNationalLab,OakRidge,TN37831,USA)

AbstractThetransverseemittanceofanionbeamdescribesitstransversesizeastheparticlesaretransportedfromasourcetoatarget.Itallowsforpredictingbeamlossesinlimitingaperturesandthebeamfocussizeatthetarget.Variousde nitionsandissuesarediscussed.Themostcommonandemergingmeasuringtechniquesarepresented,includingtheiradvantages.Severalmethodsofemittancedataanalysis,theiraccuracyandtrustworthiness,arediscussed.

Keywordsionbeams,ionbeamtransport,ionbeamemittance,ionbeamdiagnostics,emittanceanalysis

1Introduction

Thenormalizedemittanceofachargedparticle

Theequalsignappliesforuncorrelatedxandycoordinates.Theshape-dependentformfactorχisabout2.Emittancesaretheproductofalengthandananglewithunitsofm·rad,mm·mrad,orsim-plymorµm.Semi-axesproductsareoftengivenwiththeunit“π·m·rad,”whereπisasymbolandnotamultiplier,whichfollowsaratherunconven-tionalsuggestion.Confusionisavoidedbystatingwhetherthegivenvaluesrepresentvolumes,areas,orsemi-axisproducts.

Theinterestinemittanceemergedwiththedevel-opmentofaccelerators,andseveralreviewshavebeenpublished

[1—4]

[1]

beamisconservedalongitsaxisofpropagation(Liou-ville’stheorem)aslongastheparticlesaresubjectedtoconservativeforces,suchastheelectricandmag-netic eldsusedfortheirtransport.Hencetheemit-tanceallowsfordesigningminimum-lossbeamtrans-portsystemsandforpredictingthoselosses.Thisisimportantforchargedparticlebeamfacilitiesintheirquestforhighertargetyields,andessentialforhigh-poweracceleratorswherelosseslimitoperation.

Thetransverseemittanceisthefour-dimensionaldistributionofallpositioncoordinatesalongthetwotransversecon guration-spacedirectionsandtheiras-sociatedvelocitycoordinates.SometimesemittancesaregivenasvolumesVxyorasorthogonal,two-di-mensionalprojectionsAxandAythatareoccupiedbyacertainfractionofthebeam.Butmostfrequently,theemittancesεaregivenassemi-axisproductsofequal-area(/-volumehyper-)ellipses.

Vxy=εxy·π2 εx·εy·π2/χ=Ax·Ay/χ.

[1]

.Thispapergivesabriefoverviewand

anupdateonthemostpopularandemergingtech-niquesformeasuringandanalyzingtransverseemit-tancesoflow-energycharged-particlebeams.

2Measuringemittanceareas

Anadjustablelensandtwobeampro lemonitors

separatedbya eld-freedriftlengthL,oralterna-tivelytwosetsofadjustableslitsandalargeaccep-tanceFaradaycupdownstreamofthesecondslit,are

低能离子束横向发射度的测量及分析

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184 (HEP&NP) 31

低能离子束横向发射度的测量及分析

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低能离子束横向发射度的测量及分析

186 (HEP&NP) 31

x2 · x 2 x·x 2,

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