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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R10S(x)dx=R11S(x)dx=1=2R10S(x)dx. ingure2.7.Itisworthwhiletomentionthatthepointx=1isthemid-totalintegralpoint: 105cE4=(22),wherethenumericalfactoristheSand'sdenitionoftheradiationconstantE wherePtotistheinstantaneoustotalSRpoweremitted:inpracticalunits(GeV/s),Ptot=8:8575 andaretheelectronenergyinGeVandtheradiusoftrajectorycurvatureinmeters.S(x) inEqn.(2.16)istheso-calledUniversalfunction,S(x)=9p3 8xR1xK5=3(x)dx,whichisplotted chrotronradiationisproportionaltotheUniversalfunction. 2.5RudimentsonFEL-oscillatorTheory Figure2.7:PlotoftheUniversalfunctionS(!=!c).Thefrequencydistributionofthetotalsyn- Despitethefactthepresentreportdoesnotspecicallydealwiththephotonbeamgenerated free,indeeditmeanstheyareunbounded(contrarytoconventionallaser)butthereareconnedin amagnetostaticregionsincethefreeelectronswillnotradiateunlesstheyareexperiencingsome kindofacceleration. Asinaconventionallaser,FELconsistsinthreemainprocesses:(i)aspontaneousemissionis providedbysynchrotronradiationemittedaselectronswiggleinamagnet;(ii)theso-generated bytheIRFEL,webrieyexplainthebasesofFELtheorysincetheywillenablethereaderto all,weshouldnotethatthewordfreeinfree-electronlaserdoesnotmeanthattheelectronsare understandbettertherequirementsonthedriver-acceleratorelectronbeamparameters.Firstof radiationisrecirculatedinaresonator;(iii)andisampliedasitcopropagateswiththeelectron amagnetthatgeneratesaspatiallyperiodicmagnetostaticeld.InthecaseoftheIRFELof InaFEL,thespontaneousemissionisgeneratedastheelectronsareinjectedintoawiggler, beam(stimulatedemission). JeersonLab,theundulatorisaplanarone:itconsistsintworowsofNupermanentmagnets ofoppositepolaritiesstackedtogetherwithaperiodu;therowareseparatedbyaxgapas 2.5.1UndulatorRadiation S( ω/ω c ) 1 0.1 0.01 0.001 0.0001 0.001 0.01 0.1 1 10 ω/ω c

000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 000000000000000000000000000000000000000 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 111111111111111111111111111111111111111 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 000000 000000 000000 000000 000000 000000 000000 000000 000000 000000 111111 111111 111111 111111 111111 111111 111111 111111 111111 111111 000 000 000 000 111 111 111 111 00 00 00 11 11 11 01 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 11111111111111111111111111111111111111111111 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 0000000000000 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 1111111111111 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0000000000000000000000000000000000 1111111111111111111111111111111111 0000 0000 0000 0000 0000 0000 1111 1111 1111 1111 1111 1111 0000 0000 0000 0000 0000 0000 0000 0000 0000 1111 1111 1111 1111 1111 1111 1111 1111 1111 0000 0000 1111 1111 00000 00000 00000 00000 00000 00000 00000 00000 11111 11111 11111 11111 11111 11111 11111 11111 000000 000000 000000 000000 000000 000000 000000 111111 111111 111111 111111 111111 111111 111111 Electron Beam Resonant Cavity Length = 8.02 m Photon Beam λ u Figure2.8:FEL-oscillatorprinciple(CourtesyJ.Martz,JeersonLab). schematicallydescribedingure2.8.Insuchcongurationthegeneratedmagnetostaticeldis transversewithrespecttotheelectronvelocity.Aselectronstravelinthewiggler,theyareslightly deectedalternativelyupanddown(seeFigure2.8)andtherebyspontaneouslyemitsynchrotron radiationthatislinearlypolarized(inthecaseofaplanarwiggler). InthecaseofIRFEL,theundulatorproducesaweakmagnetostaticeldoftypically0.4Tesla. Theelectrontrajectorywhenitislocatedwithintheundulatorpolesisdescribedby: y=acos(2z=u) (2.17) dy dz=2a ucos(2z=u) Theforceontheelectronatthemaximumcurvaturecorrespondstothepeakvalueofthe magneticeld!B:=mec=(eB).Itiscommontocharacterizetheundulatormagnetbytheso calleddeectionparameterKdenedasK=dy=dzjmax=2ua.Togetherwiththerelation (2=)2a=eB=(mec),Ktakestheform:K=eBu 2mec (2.18) thisdeectionparameteristhemaximumangularexcursionofthebeaminunitsof1=.Itis interestingtocomputethemaximumamplitudeinthecaseoftheIRFEL:a=Ku=(2)'60m whichissmallerthattheelectronbeamsizesatthislocation(x'y'200m). Thewavelengthoftheradiationemittedbytheundulatorisdeterminedbythetimecontraction factordt=dt0=1cos,tbeingthetimereferenceinthemovingframewhereast0isthelaboratory (i.e.undulator)time.Intheelectronrestframe,theelectron\sees"theNuperiodsofthewiggler

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<strong>Electron</strong><br />

<strong>Beam</strong><br />

Resonant Cavity Length = 8.02 m<br />

Photon <strong>Beam</strong><br />

λ u<br />

Figure2.8:FEL-oscillatorprinciple(CourtesyJ.Martz,JeersonLab).<br />

schematicallydescribedingure2.8.Insuchcongurationthegeneratedmagnetostaticeldis<br />

transversewithrespecttotheelectronvelocity.Aselectronstravelinthewiggler,theyareslightly<br />

deectedalternativelyup<strong>and</strong>down(seeFigure2.8)<strong>and</strong>therebyspontaneouslyemitsynchrotron<br />

radiationthatislinearlypolarized(inthecaseofaplanarwiggler).<br />

InthecaseofIRFEL,theundulatorproducesaweakmagnetostaticeldoftypically0.4Tesla.<br />

Theelectrontrajectorywhenitislocatedwithintheundulatorpolesisdescribedby:<br />

y=acos(2z=u) (2.17)<br />

dy<br />

dz=2a<br />

ucos(2z=u)<br />

Theforceontheelectronatthemaximumcurvaturecorrespondstothepeakvalueofthe<br />

magneticeld!B:=mec=(eB).Itiscommontocharacterizetheundulatormagnetbytheso<br />

calleddeectionparameterKdenedasK=dy=dzjmax=2ua.Togetherwiththerelation<br />

(2=)2a=eB=(mec),Ktakestheform:K=eBu<br />

2mec (2.18)<br />

thisdeectionparameteristhemaximumangularexcursionofthebeaminunitsof1=.Itis<br />

interestingtocomputethemaximumamplitudeinthecaseoftheIRFEL:a=Ku=(2)'60m<br />

whichissmallerthattheelectronbeamsizesatthislocation(x'y'200m).<br />

Thewavelengthoftheradiationemittedbytheundulatorisdeterminedbythetimecontraction<br />

factordt=dt0=1cos,tbeingthetimereferenceinthemovingframewhereast0isthelaboratory<br />

(i.e.undulator)time.Intheelectronrestframe,theelectron\sees"theNuperiodsofthewiggler

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