1 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale2 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale Total length 35.0 cm!Diameter 69.4 cm!Accelerating gap 4 cm!Frequency 187 MHz!Q0 30887!Operation mode CW!Gap voltage 750 kV!Field at the cathode 19.47 MV/m!Peak surface field 24.1 MV/m!Stored energy 2.3 J!Shunt impedance 6.5 MΩ"RF Power 87.5 kW"Peak wall power density 25.0 W/cm2!3 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale4 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale5 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale6 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale7 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale8 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale9 A CW Normal Conductive RF Gun for FELs & ERLsF. Sannibale10 A CW Normal Conductive RF Gun for FELs & ERLsF. Sannibale11 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale12 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale13 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale14 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale15 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale16 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale17 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale18 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale19 A CW Normal Conductive RF Gun for FELs & ERLs F. Sannibale J. Staples, F. Sannibale, S. Virostek, "VHF-band Photoinjector", CBP Tech Note 366, October 2006 S. Lidia, et. al., ”Development of a High Brightness VHF Electron Source at LBNL”, Proceedings of the 41st Advanced ICFA Beam Dynamics Workshop on Energy Recovery Linacs, Daresbury Laboratory, UK, May 21-25, 2007. J. W. Staples, et al., "Design of a VHF-band RF Photoinjector with MegaHertz Beam Repetition Rate". 2007 Particle Accelerator Conference, Albuquerque, New Mexico, June 2007. K. Baptiste, et al., "A CW normal-conductive RF gun for free electron laser and energy recovery linac applications", to appear on NIMA.20 A CW Normal Conductive RF Gun for FELs & ERLs F. SannibaleRecent Improvements to the IMPACT-T Code and Applications to Ion Back Bombardment and Initial Density ModulationImpact-T Particle-In-Cell Monte-Carlo Simulation Ion Back Bombardment H2+: for 0 MHz, 100 MHz, and 200 MHz RF FrequenciesFeatures of IMPACT-T • Parallel PIC code using time “t” as the independent variable Emission from nano-needle tip including Borsch effect • Key Features — Detailed RF accelerating and focusing model — Multiple Poisson solvers • 3D Integrated Green Function • point-to-point — Multiple species — Cathode image effects — Wakes — CSR (1D) — Monte-Carlo gas ionization — Run on both serial and multiple processor computersModeling Ion Back Bombardment • Reduce the quantum efficiency of the photo cathode • Limit the lifetime of the photo cathode QE scans over many weeks operation at Cornell Photocathode C. K. Sinclair, et. al, PRSTAB 10, 023501 (2007)• PIC-Monte Carlo Method – Electron macroparticle transport following quasi-static PIC method (including both space-charge effects and external fields) – For each electron macroparticle within each time step dt, the probability of ionization is: • P = 1 – exp(-n σ v dt)"– A uniform distributed random number R is generated: • If R < P, ionization occurs and an ion macroparticle is generated – Neglect the ionization collision effects on electrons – Ion momentum distribution is assumed to be a Gaussian distribution with given gas temperature – Ion particle transport subject to external fields and SC fields of electrons Computational ModelApplication Example: H2+ Gas Pressure = 10-6 Torr Temperature = 300 K Electron charge = 0.8 nC Electron distribution = beer can (1mm) and flattop 104 ps Electron repetition rate = 1 MHz Cross section of H2 -->Ez on axis kinetic energy vs. distance transverse rms size vs. distancce Electron Beam Evolution in the RF Gun with Space Charge Effects (0.8 nC)– CORT signal is observed at LCLS linac before BC1 – This is believed to be due to microbunching effects – Initial density modulation causes energy modulation – Space-charge effects help smear out the energy modulation – Short wave density modulation needs large number of particles and longitudinal mesh points: – 1 um modulation requires >= 10,000 grid points and 100 million macroparticles – Particle-field decomposition for good load balance and memory usage. Large-Scale Simulation of Initial Density Modulation in LCLS PhotoinjectorTransverse RMS Emittance Evolution w/o 20% 50 um Density ModulationCurrent Modulation with Initial 20% Density ModulationUncorrelated Energy Modulation with Initial 20% Density ModulationUncorrelated Energy Modulation with Initial 20% Density