Photo-cathode RF-gun System - KEK

High Energy Accelerator Research OrganizationPhoto-cathodeRF-gunExperiments at KEK-ATFR. KurodaM.Washio, , S. Kashiwagi, , K. Hasegawa*,M. Kuriki**, H. Hayano**, J. Urakawa**, X. J. Wang***Research Institute for Science and Engineering, Waseda University, Japan*Tokyo University of Science, Japan**High Energy Accelerator Research Organization, Japan***Brookhaven National Laboratory, USAResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationOutlineIntroductionWhat’s the RF-gunManufacturing and Resonant Frequency TuningPhoto-cathode RF-gun Experiment at KEK-ATFmotivation : Purpose of ExperimentsExperimental Setup : Injector, LaserResults of Experiments : Injector, L0 - BT end, DRSummary and Future Works(in case of Waseda University)Evaluation of the electron beam generated from the RF-gunSimulation and ResultsResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationWhat’s s the RF-gunRF-gun imageUV pulse LaserPhoto CathodeThe RF-gun is the very compact electron injector system.Electron BeamThe RF-gun has 1.6 cell S-band cavity made from copper.The Cross Section of The RF-gun CavityResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationManufacturing RF-gun CavitiesIn order to reduce the dark current, a diamond turning method hasbeen applied for a fine manufacturing of the RF-gun cavities.Good flatness & cleanness inside of cavitiesFine machining using diamondturning techniqueHalf CellFull CellResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationCombining CathodeCathode PlateRF-gun Cavity without CathodeRF-gunResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationResonant FrequencyTuningAspect of FrequencyMeasurementResults of Resonant Frequencyusing Network AnalyzerResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationRF-gun SimulationComputer Simulation for RF-gunEvaluation of Beam Characteristicsunder the various kinds of ParametersN YLF 4th HarmonicParameters for the Simulation46Electron Beam0 102.21-46Image of RF-gun simulationWavelengthPulse shapePulse lengthSpot sizeAcc. GradientCavity Frequency262 nmgaussian10 ps (FWHM)1.2 mm100MV/m2.856GHz (p mode)Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research Organization3020Results of the SimulationX' [m rad]100-10-20-30-4 -3 -2 -1 0 1 2 3 4X [mm]Emittance DistributionChargeEnergy1nC5MeVRMS Emittance [mm mrad]20815RMS Emittance [mm mrad]Energy [MeV]765104352100 20 40 60 800100Phase [degree]Energy [MeV]Bunch Length10 ps (FWHM)Emittance and Beam EnergyEmittance (Norm.)3mm mradElectron Beam Characteristics from RF-gunResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationAccelerator Test Facility (KEK-ATF )Photo-cathode Prove of Principle RF-gun for JLC ExperimentBeam Sourceat KEK-ATFOutlineThe RF-gun Experimentmotivation : Purpose of Experimentsat KEK-ATFExperimental Setup : Injector, LaserResults of Experiments : Injector, L0 - BT end, DRSummary and Future Works50.4m120mResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationMotivation : Purpose of ExperimentsThermionic gun system (including SHB and Buncher) at KEK-ATF1. Long tail beam2. Beam lossLaser-driven Photo-cathode RF-gun(BNL type 1.6 cell S-band)1. Low Emittance BeamHigh Gradient AccelerationDecrease in Space Charge Effect2. Short bunch (No tail)Bunch length and structure can be controlled by laserNo buncher system required Compact SystemDecrease the Beam LossWe have performed characterization of photo-cathode RF-gun system bycomparing with thermionic gun system at KEK-ATF.Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationHoweverWe could not use a new RF-gun cavity and cathodebeacause we had no time for manufacturing the new one.We installed the prototype RF-gun (non-diamond turning, Copper Cathode)which used for a long time at Tokyo University.RF-gun at Tokyo UniversityResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationExperimental SetupInjector part of KEK-ATFRF Gun CavitySolenoidFaraday CupL0 (3m Acc.Structure)ICTWire ScannerResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationExperimental SetupFront View of the ATF-Injector with RF-gunResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationExperimental SetupPicosecond Nd:YLFLaer System (pulrise V)Control BoxNd:YLF LaserResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationExperimental SetupPicosecond Nd:YLFLaer System (pulrise V)Laser Medium : Nd:YLFWave Length : 262 nmPulse Width : 10 ps(FWHM)Energy : 50 uJ/pulseLaser Profile(measured by CCD Camera)X:2.1mm(FWHM)Y:1.0mm (FWHM)at CCD camera•Timing stabilizer(119MHz seed light) Intensity stabilizer(25 Hz UV light)Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationResults of Experiments (Injector part)Emittance Measurement(Measured by Wire Scanner)Measurement Results (Single bunch : Rep. 6.25Hz)Energy : 78.0 MeVdE/E : 3.5 % (Full Width)Charge : 0.810 10 e-/bunch (1.2nC/bunch)Bunch length : 14.0 psec (FWHM)Normalized emittance X : 13.3 mm mradY : 18.2 mm mradResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationExperimental SetupDamping ring layoutML8TMS4TICT(BT End)ICT(L0 out)DCCT ICT(DR)ICT(BT Middle)ICT(Linac End)ML15LMS1TWe have tried to pass the beam through the damping ring.Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationResults of Experiments (L0 - BTend part)L0 – BTend TransmissionRF gunTrans.Ratio : 100%jitter : 3.6% (L0) , 3.7% (BTend)ThermTherm+SHBTrans.Ratio : 60%jitter : 1.2%(L0) ,4.9%(BTend)Results of Experiments (DR part)One of the Q-magnets in DR was out of orderWe could not storage the beam in DR completely.But, at several turns the beam transmission wasabout 100 %.Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationSummaryWe confirmed that the Photo-cathode RF-gun system have a goodperformance at KEK-ATF.Beam transmission was achieved up to 100% in case of the L0-BTend part.We can suggest that the beam will be passed through the DR completelyin near future.The emittance of the beam from RF-gun was not as small as we have expected.The RF-gun cavity and cathode was used for a long time at Tokyo University.Future WorksWhy ?The surface of the cathode has many craters.We will design and manufacture the new RF-gun cavity and cathode for themulti-bunch beam.Test experiment for the multi pulse laserResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationRoughness of the cathode surfaceThe Copper Cathode of the RF-gunThe surface of the cathode has many craters.These craters are a cause of the emittance growth.Research Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationSummaryWe confirmed that the Photo-cathode RF-gun system have a goodperformance at KEK-ATF.Beam transmission was achieved up to 100% in case of the L0-BTend part.We can suggest that the beam will be passed through the DR completelyin near future.The emittance of the beam from RF-gun was not as small as we have expected.The RF-gun cavity and cathode was used for a long time at Tokyo University.Future WorksThe surface of the cathode has many craters.We will design and manufacture the new RF-gun cavity and cathode for themulti-bunch beam.Test experiment for the multi pulse laserResearch Institute for Science and Engineering, Waseda University

High Energy Accelerator Research OrganizationFuture Plan of the Multi Bunch Beam Generationusing RF-gun System at KEK-ATFCathode Material : Cs 2 TeQE : ~10 %Laser Energy : 50 ~ 100 nJ/pulseLaser Medium : Nd:YLF or Nd:VANLaser Wave Length : 266 nm ( 4 th harmonic)Bunch Charge : 1 nC/bunchBunch to Bunch : 2.8 ns (357 MHz seed lights)Number of Bunches : 20 bunch/train or 100 bunch/train (in future)Research Institute for Science and Engineering, Waseda University