G8 自由电子激光原理_黄志戎.ppt

FELprinciple黄志戎 ZhirongHuang 自由电子激光原理 1Dtheory LectureOutline SASEandXFEL FELR D 3 Asolutionlookingforaproblem LightBulbvs Laser A Schawlow Nobelprizeonlaserspectroscopy ScientificAmericans 1968 Radiationemittedfromlightbulbischaotic Pinholecanbeusedtoobtainspatialcoherence Monochromatorcanbeusedtoobtaintemporalcoherence PinholeandMonochromatorcanbecombinedforcoherence Laserlightisspatiallyandtemporallycoherent ProducedbyresonantinteractionofarelativisticelectronbeamwithEMradiationinanundulator FreeElectronLaser FEL Tunable Powerful Coherentradiationsources JohnMadey InventoroftheFEL 1971 ThreeFELmodes SR Brightlightsourcesfromrelativisticelectrons Electronsemitwithrandomphase radiationintensity N gisLorentzfactor Nisnumberofelectrons 109 Synchrotronradiation Undulatorradiation LinacCoherentLightSource LCLS atSLAC Injector X FELbasedonlast1 kmofexisting3 kmlinac 1 5 15 14 4 3GeV ProposedbyC Pellegriniin1992 EraofXFEL 2009 XFELsareExtremelyBrightandUltrafast time XFEL1012photons Synchrotron106photons 100fs 10ps Note synchrotronsourcesaremuchhigherrep ratethanXFELs OrderedStructuresEquilibriumPhenomena DisorderedStructuresNonequilibriumPhenomenaTransientStates 1900 2000 future EraofCrystallineMatter EraofDisorderedMatter CoherentX rayProbes ConventionalX rayProbes FutureRoleofFELsandAdvancedSources H Dosch DESY Undulatorradiation Worksforharmonicslh l1 h UVSOR Okazaki Japan lu forwarddirectionradiation andharmonics undulatorparameterK 0 94B Tesla lu cm Canenergybeexchangedbetweenelectronsandco propagatingradiationpulse l1 LCLSundulatorK 3 5 lu 3cm e beamenergyfrom3GeVto15GeVtocover 1 30 to1 2 ElectronandPhotonInteraction Resonantinteraction energy 0 0phase k1 ku z 1t radiationwavenumber undulatorwavenumber Usevariables arrivaltimeatundulatordistance FELlongitudinaldynamics classicaltheory Longitudinalelectronmotionincombinedundulatorandradiationfieldsdescribedbypendulumequations forplanarundulator 1forhelicalundulator PendulumEquation Low gainregime Gainperpassissmall ignoreMaxwellequation Useonlyparticlemotionandenergyconservation Radiationgain Radiationloss Radiationfrequency High gainregime S Reiche log radiationpower distance electronbeam photonbeam e beamdump undulator Useslowlyvaryingphaseandamplitudeapproximation Beamcrosssectionarea 1DWaveEquation Transverseelectricfield Transversecurrent saturationefficiency r 10 3forshort wavelengthFELs FELPierceparameter IA 17kAisAlfvencurrent Bothpendulumequationandwaveequationcanbescaledbyasinglescalingparameter High gainsolution IllustrateFELgainbyneglectingqdependenceofEfield slippage Power Exp im3 2rkuz 2 gainlength Cubicequationandsolution Slippageleadstocoherencelengthandspikystructure Duetoresonantcondition lightovertakese beambyoneradiationwavelength 1perundulatorperiod interactionlength undulatorlength z Slippagelength 1 Nundulatorperiods at1 5 LCLSslippagelengthis ls 1 5fs 100 fspulselength Eachpartofopticalpulseisamplifiedbythoseelectronswithinaslippagelength anFELslice Coherencelengthisslippageover 2LG lc ls 10 ML Dz lcindependentradiationsources modes N 1 e x rays 1 m P Emma FELstartupfrome beamnoise BW 0 6 BW 0 15 BW 0 10 BW 0 08 spikytemporalstructure narrowband width Allverticalaxesarelogscale Duetonoisestart up SASEischaoticlightwithMLcoherentmodes i e spikesinintensityprofile LongitudinalphasespaceisMLlargerthanFourierTransformlimitSASEenergyfluctuationis MLisnotconstant reducedbyincreasedcoherenceduringexponentialgrowth andincreasedwithreducedcoherenceaftersaturationLCLSnearsaturation 50fs ML 200 W W 7 Statisticalintensityfluctuationdeterminedbynumberoflongitudinalmodes FELBandwidthsetbyFELParameter r 10 3 LCLSspectrum Spectralpropertiesaresimilartotemporaldomain exceptthateverythingisinverted Example LCLSrelativespectralspikewidth Dz 50fsbunchlength width 5 10 6Dz 5fsbunchlength width 5 10 5Dz 0 5fsbunchlength width 5 10 4 spikewidth l1 2Dz Bandwidth 2 SASE1DSummary Powergainlength Exponentialgrowth P z P0exp z LG Startupnoisepower P0 r2gmc3 l1 spontaneousradiationintwogainlengths Saturationpower Psat r e beampowerSaturationlength Lsat lu r 18LGFWHMbandwidthatsaturation 2rCoherencelengthatsaturation lc l1 pr 3 5m 1 5kW 20GW 60m 0 1 0 2fs S Reiche Z 25m Z 37 5m Z 50m Z 62 5m Z 75m Z 87 5mm Singlemodedominates closeto100 transversecoherence Transversecoherence PeakBrightnessEnhancementFromStorageRingLightSourcesToSASE EnhancementFactor ofphotons Nlc 106to107 UndulatorinSR SASE e eNlc x y 2 x 2 y Z compressed B 1023 1033 1010 Nlc numberofelectronswithinacoherencelengthlc to1011 SASEFELElectronBeamRequirements eN 0 5 mat1 15GeV 0 04 atIpk 3kA K 3 lu 3cm 18LG 100mforeN 1 5 m Wemustincreasepeakcurrent preserveemittance andmaintainsmallenergyspreadsothatpowergrowsexponentiallywithundulatordistance z P z P0 exp z LG FELpowerreachessaturationat 18LGSASEperformancedependsexponentiallyone beamquality challenge transverseemittance relativeenergyspread FELgainlength Photocathoderfgun xn 1mm Ip 100ABunchcompressionIp 2 5kA Dt 1 100fsAcceleration3 20GeV l lu 2g2 adiabaticdamping x xn g l 4p sg g r 10 3Undulator100 mlong segmented afewmmtoleranceProjectsundertakenatUS Germany Japan Korea Swiss Italy emittance corrector rfphotocathode gun Linac Linac Linac Pulsecompressors SASEUndulator XFELacceleratorsystem LCLS world sfirsthardx rayFEL SASEwavelengthrange 30 1 2 Photonenergyrange 0 4 10keVPulselengthFWHM5 100fs 5 500fsforSXRonly Pulseenergyupto4mJ 95 acceleratoravailability 1 5 SASEWavelengthrange 3 0 6 Photonenergyrange 4 20keVPulselength 10fsFWHM Pulseenergyupto1mJ Spring 8SACLA2011 MoreXFELstocome moretocome PAL XFEL 2015 SwissFEL 2016 LCLS II 2020 32 EuropeanXFEL 2016 SRFtechnology driverforhigh averagebrightnessFELs XFELcavity LCLS IIAcceleratorLayoutNewSuperconductingLinac LCLSUndulatorHall LCLS IIFACReview July1 2 2014 Twosources highrateSCRFlinacand120HzCuLCLS IlinacNorthandSouthundulatorscanoperatesimultaneouslyinanymode 1 0 25keV 120Hz 1 0 5keV 120kW 0 2 1 3keV 120kW 4GeVSCLinac CuLinac Concurrentoperationof1 5keVand5 25keVisnotpossible 4GeV 0 3mA 1 2MW SCRFLinacin1stkmofSLACtunnel ExistingLCLS WhatcomesnextforXFELR D Precisecontrolx raypropertiessimilartoopticallasersCompactcoherentsources SASEtemporalcoherencecanbedrasticallyimprovedbyseeding selforexternalseeding oranx rayoscillator SASE seeded chicane 1stundulator 2ndundulator SASEFEL grating SeededFEL grazingmirrors slit Self Seeding1 2 FirstundulatorgeneratesSASEX raymonochromatorfiltersSASEandgeneratesseedChicanedelayselectronsandwashesoutSASEmicrobunchingSecondundulatoramplifiesseedtosaturation Longx raypathdelay 10ps requireslargechicanethattakespaceandmaydegradebeamqualityReducechicanesizebyusingtwobunches3orsingle crystalwakemonochromator4 1 J Feldhausetal NIMA 1997 2 E Saldinetal NIMA 2001 3 Y Ding Z Huang R Ruth PRSTAB 2010 4 G Geloni G Kocharyan E Saldin DESY10 133 2010 Hardx rayself seeding LCLS Geloni Kocharyan Saldin DESY 1GW 25GW FELspectrumafterdiamondcrystal Self seedingof1 mme pulseat1 5 yields10 4BWwithlowchargemode 37 10 5 15 51 16 17 31 HXRSSatLCLS replacingU16 Braggdiagnosticwithcamera Chicanemagnet Diamondmonochamber 38 X rays J Amann P Emma 8 3keV 20eV SASEspectrum diamondOUT Factorof40 50BWreduction diamondIN Awellseededpulse nottypical SASE 0 45eV 5 10 5 insertdiamond turnonchicane 0 45eV chicaneOFF chicaneON J Amannetal NaturePhoton 2012 FourierTransformlimitis5fs chicane e Undulator2 7 Undulator10 18 SASEFEL grating SeededFEL M1 slit FEL X rays M2 M3 40 P Montanezet al Softx rayself seeding 0 5 1keV 4m 41 Electronenergy FELPower Electronenergy FELPower Seededbandwidthisafactorof 30narrowerthanSASEatphotonenergy860eV designrange500 1000eV witharesolvingpowerofabout5000 10 shotaveragedspectralbrightnessisafactorof 4higherthan2 5mJSASE Carefulalignmentsofelectronandseed10 shotaveragespectracomparison Seedingresults Feb 17 2014 Jitterreduced 42 S Wakatsuki F J Decker A Lutman etal Byadjustingtheyawangleinadditiontotheusualpitchangleoftheseedingcrystal two colorseededFELwithtwodifferentcrystaldiffractionplaneswasdemonstratedatthehardx rayphotonenergiesatLCLS 2 colorself seedingforMADphasing 45eVseparation Generatetwobunchesbystackinginjectorlaser Accelerateoff crestandcompresstoget upto200fsseparation 1 energyseparation1mJinSASEoperation improvementby 10withrespecttopreviousschemes A Marinelli etal 2 bunchtoprovideindependentcontroloftimeandenergyseparationtoenableMADandpump probeexperiments 43 2 bunch2 colordevelopment 44 C Behrens Y Ding P Krejciketal NatureComm 2014 Electronbeamisstreakedhorizontallyandviewedonascreeninaverticallyresolvedenergyspectrometer revealingtime energyphasespaceaftertheFELundulator Theupperrightplotsshowanexampleofanultra shortsoftx raypulsewithameasured2 6 fspulseduration Femtosecondx raydiagnosticswithXTCAV XTCAVexample 150pC 10keV Tapersection C Schroeder FLS2012 LaserPlamsaA