Yc Desy Tud 2013

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Bunch Emission Simulation for the PITZ* Electron Gun Using CST Particle StudioTMYe Chen, Erion Gjonaj, Wolfgang Mller,Thomas WeilandDESY-TUD Meeting 09.08.201309. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |7. August 2013| Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Prof. Dr.-Ing. Thomas Weiland| 1The European XFEL is more than three kilometers long. It will begin at the DESY site in Hamburg-Bahrenfeld and run to the town of Schenefeld, where the main building with its underground experiment hall will be located.ContentsIntroduction CST field simulationEigenmode simulation for Gun 4.3 cavitySolenoids simulationCST PIC simulation Modified simulation modelASTRA particles importSimulation resultsDiscussionCathode studiesNext steps09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Introduction Motivation Main tasks 3D CST field simulations (Gun 4.1/4.3 cavity, Solenoids)3D CST beam dynamic simulationsfor different bunch charges with homogeneous/inhomogeneous particle distributionsconvergence study and comparisons to ASTRA Cathode studiesInfluences from materials, non-uniformities, on beam qualitiesEmittance study09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |CST Field SimulationSimulation resultsMode modeField Ratio1.04Frequency1.3019 GHzEigenmode Calculations

Accelerating Ez field along z-axiszEz

Simulation Model for Gun 4.3 Geometry Settings/mm55100180.64179.902010009. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |7. August 2013| Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Prof. Dr.-Ing. Thomas Weiland| 4CST Field (Solenoids) Simulation Pos. of Main = 276 mm Pos. of Bucking = -172 mm Curr. of Main = 375 A Curr. of Bucking = -31 A Bzmax 0.2279 T Bz(0,0,0) 10-7 T

Geometrical Settings/cm

Simulation Modelfor Solenoids

Longitudinal B field along z-axisBzz09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |PIC Simulation ModelMin. mesh step= 0.01mmMeshcell numbers: up to 1000MIncluding PIC position monitor, phase-space monitors for momentum, energy, velocity , 2D particle monitors and particle import interfaces

electron bunch2D Particle Monitors: transversal/longitudinalParticle Import InterfaceLocal Mesh Refinement CST PIC SimulationBunch Parameters & Fields Data Bunch radius = 0.4 mm Bunch charge = -1 nC Bunch length = 21.5 ps Rise/Fall time = 2 ps Macro particles = 500 k Cavity frequency = 1.30 GHz Ez at cathode = 60.58 MV/m Field ratio = 1.04 Bzmax = 0.2279 T09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |CST PIC Simulation

Amplitude of EzzImported longitudinal electric field along z-axis for PIC simullationfield interpolation at the cathode planeProblem descriptionmesh resolution difference in the cathode region between eigenmode simulation and PIC simulation can lead to field interpolation at the cathode planefield interpolation within the first meshcell between PEC and vacuum Solutionskeep the mesh resolution same, but very mesh-consumingmodify PIC simulation model09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |CST PIC SimulationGoalto improve the accuracy of the field solution within a short distance from the cathode plane at z = 0Implementationsend positrons & electrons at the same timeall velocity directions reversedkeep field ratio same

Longitudinal E field in the mirrored cavityzEzelectron bunchpositron bunchMirrored gun model for PIC09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |

Note that,simulations with both of the models showed trends of convergencebetter convergence rate with the mirrored model43.532.521.510.5040353025201510500 250 500 750 1000 1250 1500Xrms /mmDiscrepancy /%z /mmCST-1, z0.075mmCST-2, z0.05mmCST-3, z0.03mm, with original modelASTRA SimulationDiscrepancy with ASTRA for CST-3CST-5, z0.015mmCST-4, z0.03mm, with mirrored modelDiscrepancy for CST-3ASTRACST-1CST-2CST-3CST-5CST-4horizontal rms size of the beam along z-axis (Gun4.1)Discrepancy with ASTRA for CST-5Discrepancy for CST-5CST PIC Simulation09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Lt=21.5E-3nsrt=2E-3nsLE=0.00055keVsig_x=sig_y=0.4mmQ =1nCIpart=500,000

Species=electronsDist_z=pDist_pz=iDist_y=Dist_x=rDist_px=Dist_py=rRef_zpos=0.0mInput Data for ASTRA:ASTRA Particle ImportParticles z=z0, t(t0,t1) Astra2CSTParticles t=t0, z(z0,z1)Particle Import Interface(CST-PS)CST PIC Simulation09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |CST PIC Simulation

average energy of the beam along z-axis09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |7. August 2013| Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Prof. Dr.-Ing. Thomas Weiland| 11CST PIC Simulation

horizontal rms size of the beam along z-axis

beam energy spread along z-axis09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |CST PIC Simulation

bunch length of the beam along z-axis

horizontal normalized emittance of the beam along z-axis09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Discussion Cathode StudiesSurface impedance: Frequency-dependent isotropic surface impedance model

Gun cavity materialCathode material

Gun 4.3 Cavitycathode plane at z = 0yz : conductivity, : angular frequency09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Cathode StudiesSpace charge field vs. time in correspondence to various conductivities of cathode materialSPCH Field

with bunch parameters: -1nC, 0.4mm(radius), 500k(particle numbers), 2ps/21.5ps\2psby using the same mesh resolutionduring propagation time up to 80psat the same location, z=5mmSimulation performed Time /ps09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Summary & PlansSummary Field simulations for gun 4.1 & 4.3 done, desired fields produced CST PIC results (1nC) on beam energy and spread, beam size, bunch length and beam emittance obtained, compared to ASTRA. The discrepancy with ASTRA is about 10%, 5%, 9% and 20%, respectively. Simulations on cathode study showed the influence of the cathode material on the space charge field. Plans Perform PIC simulations for various bunch chargeswith inhomogeneous particle distributions Further study on the influence of cathode material on the beam qualities09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |Thanks for your attention!09. August 2013 | TU Darmstadt | Fachbereich 18 | Institut Theorie Elektromagnetischer Felder | Ye Chen |