DESY/TEMF Meeting Status 2012

Transcription

1 DESY/TEMF Meeting Status 2012 PIC Simulation for the Electron Source of PITZ DESY, Hamburg, Ye Chen, Erion Gjonaj, Wolfgang Müller,Thomas Weiland Technische Universität Darmstadt, Computational Electromagetics Laboratory (TEMF) Schlossgartenstr Darmstadt, Germany 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 1

2 Contents Motivation & Introduction Motivation for this study Main procedures in CST Grid resolution demands 3D CST Simulation Field Simulation Gun-Cavity simulation Solenoids simulation PIC Simulation Setup Astra particle import Preliminary results Discussions Interpolation in PEC Summary & Further Steps 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 2

3 Motivation & Introduction 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 3 talk from M. Krasilnikov,Zeuthen, 2011

4 Motivation & Introduction - Main procedures in CST Simulations for gun-cavity & solenoids (CST-MWS & EMS) Tune & Calibrate external fields referring to ASTRA import data PIC simulations at a short distance of (60~130) mm (CST-PS) Beam qualities comparison between PIC simulations and ASTRA Continue PIC simulations with finer grid resolutions (Δx,Δy,Δz«0.05mm) Broaden the calculation domain as far as possible Check the results using different particle distributions Investigations with inhomogeneous particle distributions Investigate the influence of cathode (material, impurities ) Optimizations & Repeat simulations with refined parameters 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 4

5 Motivation & Introduction - Grid resolution demands for PIC simulations Δx 2, Δy 2 global mesh local mesh Bunch Region (Δx 1, Δy 1, Δz) d Δx 2, Δy 2 Part of the calculation domain Δx 1 & Δy 1 & Δz «0.05 mm d = 2X rms Δx 2 & Δy 2 (2~3) 0.05mm By properly choosing Δx 2 & Δy 2 outside the bunch region, there will be mesh-saving solutions to broaden the calculation domain in PIC simulations as far as possible. 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 5

6 3D CST Simulation-Field Simulation - Setup 1 for Gun-Cavity Simulation (CST-MWS) local mesh Geometrical Parameters L z Local mesh properties A cylinder, not included in the simulation, only for mesh refinement at the cathode. L z = Δz (mesh resolution in z, 0.01mm-0.05mm). Δx & Δy should be comparable with Δz (0.01mm-0.05mm). To obtain the field ratio we need, the radius of half cell was tuned by ~70μm. 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 6

7 Field Simulation - Gun-Cavity Simulation Results Parameters Values Algorithm JDM Accuracy 1e-6 Sym. planes used zoy & xoz Lines/wavelength 120 Mesh line ratio limit 20 Mesh resolution 0.125mm Meshcells ~14M Duration 60h Mode π mode Frequency separation 3.6MHz Field Ratio ~1.08 Frequency ~1.301GHz y z E-field H-field 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 7

8 Field Simulation Relative Error % Normalized E z ~1.08 Accelerating Ez in CST & ASTRA Astra CST (0-55) mm, RE 1% (55-75) mm, A approaches to 0 (75-105) mm, RE 2% ( ) mm, RE 0.6% z/m 9 Discrepancies of Ez in CST & ASTRA Relative Error %= Abs[A cst -A astra ]/A astra *100% A: Amplitude of E z % z/m 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 8 1 1% 0.6%

9 Field Simulation - Setup 2 for Solenoids Simulation (CST-EMS) Geometrical Parameters in cm Pos. of Main Cur. of Main Cur. of Buck 276 mm ~375 A ~-31 A 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 9

10 Relative Error% B z /T Field Simulation B z of Solenoids in CST & ASTRA B zcst B zastra B zmax =0.2279T B z0 ~10-7 T 0 z/mm Differences of B z in CST & ASTRA RE 1% z/mm December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 10

11 PIC Simulation - Setup 3 for PIC Simulation (CST-PS) Bunch parameters & External fields data Local Refinement Particle Interface 2D Particle Monitor Simulation time: 700ps so far Mini. mesh step=(0.12~0.07) mm so far Lines/λ=100~120, meshcells 115Million 1-PIC Position Monitor 18-2D Particle Monitors along the beam line from 6mm to 132mm so far Parameters ASTRA CST Species electron electron Bunch radius 0.4mm 0.4mm Bunch charge -1nC -1nC Bunch length 21.5ps 21.5ps Rise/Fall time 2ps 2ps Macro Nos. 500k 500k Frequency 1.3GHz GHz E z at cathode 60.58MV/m 60.58MV/m Field ratio ~ December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 11 B zmax T T B z_cathode 10-7 T 10-7 T Ez profile Bz profile =1%~2% =1%

12 PIC Simulation - ASTRA Particle Import Particles z=0, tє(t 0,t 1 ) Astra2Cst Particles t=0, zє(z 0,z 1 ) Particle Interface (CST-PS) Input Data for ASTRA: Lt=21.5E-3 rt=2e-3 LE= sig_x=sig_y=0.4 Q =1 Ipart=500,000 Species= electrons Dist_z= p Dist_pz= i Dist_y=Dist_x= r Dist_px=Dist_py= r Ref_zpos= December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 12

13 PIC Simulation - Preliminary results Animation of the charged particle beam in the longitudinal direction z = 132mm Mesh resolution Δz=0.12mm 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 13

14 PIC Simulation y x Animation of the transverse particle distributions y x y x z = mm z = mm z = mm y x y x y x z = mm z = mm z = mm 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 14

15 X rms /mm PIC Simulation 3.5 Beam size along the beam line PIC-0 ASTRA PIC-1 PIC-2 Astra Simulation CST-PIC Simulation-1, z=0.08mm CST-PIC Simulation-2, z=0.07mm CST-PIC Simulation-0, z=0.12mm z/m 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 15

16 x /( *mrad*mm) PIC Simulation Emittance along the beam line ASTRA ASTRA CST PIC-2, z=0.07mm CST PIC-1, z=0.08mm CST-PIC-1 CST-PIC z/m December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 16

17 Beam Energy/MeV PIC Simulation 7 6 Beam energy along the beam line ASTRA CST Beam Energy from ASTRA CST-PIC-1, z=0.07mm CST-PIC-2, z=0.12mm December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 17 z/m

18 Discussions - Interpolation in PEC Cause Difference of the grid resolution around the cathode between field simulation & PIC simulation. Outcome E z at the cathode was changed by automatic interpolation. Solutions -Keep the grid settings exactly the same around the cathode. But the field simulations turn to be much slower because of the very small grid. -Make the interpolation take place inside the cathode by shifting the back plane. But it will somehow change the eigenmode a little bit. Field Simulation 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 18 Amplitude of E z cathode Amplitude of E z cathode loading external fields Grid 1 ǂ Grid 2 PIC Simulation z/mm linear interpolation? z/mm

19 Summary & Further Steps - Summary PIC Simulation results at a short distance of 60mm downstream from the cathode showed possibilities of convergence to ASTRA simulation in terms of the beam radius by use of a finer mesh resolution (Q=1nC, grid resolution Δz 0.07mm so far ). But the current resolution is still not enough. Still no good agreement with ASTRA on the beam emittance at a short distance of 60mm by improving the grid resolution. Eigenmode convergence when setting local resolution as (Δx,Δy,Δz)<0.05mm is relatively very slow. - Steps in the near future Continue PIC simulations by enhancing the grid resolutions. Broaden the calculation domain as far as possible (60mm~200mm, Δx, Δy, Δz «0.05mm ). Check the simulations with different particle distributions(r=0.3mm). Investigate the cases with inhomogeneous particle distributions at the cathode. 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 19

20 Thank you for your attention! 17 December 2012 TU Darmstadt Fachbereich 18 Institut Theorie Elektromagnetischer Felder Dr. Ye Chen 20