Emission-related Activities at PITZ Proposals for the DFG-Networking - PowerPoint PPT Presentation

Emission-related Activities at PITZ — Proposals for the DFG-Networking "Hi 2 PE" Ye Chen for the PITZ team 22.09.2017, Helmholtz-Zentrum Berlin, Germany Contents Literature  Photoemission (PE) [1] S. Schreiber, S. Lederer, FEL 2015 [2] L. Monaco, P. Michelato, et al., EPAC 2006  Dark Current (DC) [3] D. Filippetto, P. Musumeci, et al., PRSTAB 17, 024201 (2014) [4] D. Lipka, et al., DIPAC 2011  Other (Long-Term) Topics [5] K. L. Jensen, Advances in Imaging and Electron Physics, Electron Emission Physics Vol.149, 2007 [6] E. Gjonaj, ICAP 2012 [7] R. Xiang, A. Arnold, T. Kamps, et al., PRSTAB 17, 043401 (2014) [8] P. Piot, et al., PRSTAB 16, 010102 (2013) [9] M. Zolotorev, SLAC-PUB-5896 (1992)

Further modeling requires Photoemission (PE) Studies realistic cathode laser distributions 1. (Cs 2 Te) Experimental & Numerical PE Studies Ongoing activity at PITZ and TU Darmstadt  Impacts of full EM field (RF + space charge)@cathode on PE (Cont.)  Modeling of PE in space charge dominated regime  Charge production using various RF gun and measured PC laser Radially uniform distribution parameters (simulation vs. measurement)  Dedicated studies on bunch length , slice energy spread , etc., to explain discrepancies between simulation and measurement (e.g., Bunch length in Astra systematically longer) Measured Dynamic emission process from cathode Bunch taking into account 3D full EM fields at Non-uniform charge cathode in a Lienard-Wiechert approach distribution generated Space charge according to VC2 data Charge production per simulation time step: dominated OSS signal with measured regime flattop pulse shape (old data) Quantum efficiency formulism: Measured pulse shape + length  More precise treatments needed for the modeling in space charge dominated regime  Remaining deviations w.r.t. + Possible laser intensity Field-induced work function modification: and time dependent simulations probably due to the cathode work function initial ideal beam distributions Ye Chen | Proposals for Hi2PE Networking: Emission-related Studies at PITZ | 22.09.2017 | Page 2/5 variation, e.g., in [9] plugged in the simulations

Photoemission (PE) Studies (cont.) 2. (Cs 2 Te) Investigations of a µs-scale spiky structure during electron bunch train extraction at FLASH Ongoing activity at PITZ, INFN and FLASH  Flat UV laser energy pulse train producing µs-scale spiky structure along electron bunch train  Toward modeling of RF pulse and/or laser pulse heating effect Emission issue of fresh cathode 73.3 (and some others) at FLASH, 04.02.2015, QE=10% Experiments at PITZ Fixed BSA SP ≈ 0.799 mm, 43.3 MV/m vs. 28.97 MV/m, LT=10% ~8% Set the working point in linear emission regime Laser pulse ~9% heating? Ye Chen | Proposals for Hi2PE Networking: Emission-related Studies at PITZ | 22.09.2017 | Page 3/5

Dark Current (DC) Characterization and Simulation 1. Detailed experimental DC characterization  DC vs. Solenoid current, RF power, pulse length, etc.  DC spectrum measurement Simulated DC  DC transportation DC on Low.Scr.1 patterns in [2] with 2. DC monitoring method (Z~0.85m, @6.15MW) uniform field distribution at cathode surface  Using Faraday Cups (e.g., ~10 pC resolution) DCM at PITZ  Using non-destructive resonator prototype (e.g., 0.5mV for 1µA) and XFEL 3. DC modeling and simulation based on Microscopic non- uniform E 0 Fowler-Nordheim theory uniform local field forming structures  "Realistic" cathode geometry model β 2 β 1 β 0 β 3  Surface condition determination (scanning electron Resulting in non- β i β 6 microscopy?) uniform field β 4 distribution E n at  3D dark current generator Cathode surface cathode surface  Dark current transportation studies Local field enhancement factor,  Identify critical areas for the source of dark currents by particle tracking simulations Ye Chen | Proposals for Hi2PE Networking: Emission-related Studies at PITZ | 22.09.2017 | Page 4/5

Other (Long-Term) Topics > Charge production at theoretical space charge limitation for different PC laser pulse shapes and parameters (modeling + simulation) > Cathode brightness studies with variable beam aspect ratios > "Green photocathode" studies and tests (PITZ + INFN) > Studies of slice emittance formation for various PC laser pulse shapes and for various gun field gradients (towards SC and CW regimes) > Formation of ellipsoidal electron bunches by space charge driven expansion using PITZ Pharos laser (variable PL down to ~200 fs )  Semi-analytical solution for flattop-shaped bunch in cigar regime (in [3]),  The theory may be less effective for Gaussian bunches (even more prevalent in many facilities)  In the limit of cigar aspect ratio, Maximum cathode brightness for Gaussian bunches? Thank you very much! Ye Chen | Proposals for Hi2PE Networking: Emission-related Studies at PITZ | 22.09.2017 | Page 5/5