Electron Beam Diagnostics at REGAE Shima Bayesteh September 2011

Introduction REGAE Relativistic Electron Gun for Atomic Exploration Pump-probe experiment Ultra-fast Electron Diffraction (UED) Monitors structural dymanics in the sample Exert temporal evolution of a sample To get sufficient current density to the sample for near single shot structure determinations. To avoid space-charge effects (Coulomb repulsion) that act to broaden the electron pulse while propagating from the cathode to the sample. Low-charge electron bunches. Relativistic electron beam. REGAE defines new limits in Atom Gazing Higher bunch density Micro-scale samples Higher Time Resolution

REGAE Layout Experiment REGAE Layout REGAE accelerator The whole layout

Experiment Beam parameters Electron beam energy 2-5 MeV Bunch charge 100fC -1pC Bunch length 7-30 fs Coherence length 30nm Transverse emittance 6×10-3 mrad mm rep. rate 50 Hz

Diagnostics What to Diagnose? Beam size Transverse emittance Energy & energy spread Bunch length scintillator screen pepperpot, slit magnetic dipole Ponderomotive scattering

Diagnostics Important issues in beam profile measurement A scintillator material which generates visible photons from passage of electrons in the matterial. Detection system to efficiently detect propagated light from the source.

Diagnostics Scintillator screen as source of light LYSO (Ce)* YAG(Ce) Density (g/cm3) 7.1  4.55 Decay Constant (ns) 40  70 Peak Emission (nm) 420 550 Light Yield /MeV 32000  8000 Index of Refraction 1.81 1.82 high density materials to increase energy loss by collision. Short decay time for fast timing. High light output * Cerium-doped Lutetium Yttrium Orthosilicate Ionization loss in 2-5 MeV is near to the minimum value 

Diagnostics Detection system How does Image Intensifier work?

Diagnostics Optical setup in the first diagnostics station With Intensifier Without intensifier

Diagnostics Optical setup in the 2nd and 3rd diagnostic stations 2nd station 3rd station Using a flat mirror to look at the cathode in order to do alignment for UV laser coupling to the cathode. Using a dispersive arm for energy and energy spread measurement. The same LYSO screen ia applied in this station.

No intensification yet! Dark-current shots recorded at REGAE with/out focusing No intensification yet! Diagnostics

Simulations What to simulate? Simulation tools Variety type of materials Optimization on thickness of the materials Experiment geometry to increase light collection Simulation tools Electron Gamma Shower (EGS5) transport of electrons and photons in an arbitrary geometry for particles with energies above a few keV up to several hundred GeV. Mostly to generate electromagnetic showers(Bremestralung photons and electroons from pair production) inside a medium in high energies. Better to be applied for beam simulation rather than medium simulation. Not appropriate to define complicated geometry and material such as scintillators. LITRANI stands for LIght TRansmission in ANIsotropic media (LITRANI) ROOT-based Monte-Carlo simulation , simulating light propagation in any type of set-up which may be represented by the shapes provided by the old geometry of ROOT. The program takes into account the variation of the physical parameters as a function of the wavelength such as scintillation properties, absorption length, stopping power and refractive index. for GEometry ANd Tracking (GEANT4) is a platform for the simulation of the passage of particles through matter. Geant4 includes facilities for handling geometry, tracking, detector response, run management and visualization.

Simulations Electron Gamma Shower EGS http://www2.slac.stanford.edu/vvc/egs/basicsimtool.html

Simulations Results of EGS5 With EGS we cannot go to energies lower than10 keV and in the following figures we find just energetic electrons and x-rays. Number of energetic secondaries is increasing in thicker materials

Simulations LITRANI Simulation results for 5MeV incident electrons on a crystal of 150um-thick CsITl

Simulations Estimating Dark Current value based on simulations 1 2 Counts per pixel for these two frames is comparable 1 Zemax simulation measurements Transmission factor in optics 2 Collection efficiency of the light from the source. 1 & 2  absolute calibration i.e. ….. Counts per pixel of image ≈ …… charge on the screen

Simulations Uncertainties in estimating Dark Current value based on simulations The averaged counts per pixel for both could not be exactly the same. There is a copper plate to hold LYSO whose surface behaves as a reflector. Therefore dark current could be less than estimation. Uncertainties related to the simulations

Outlook & Summary Improve simulation results with GEANT4 Compare obtained results from simulation with results achieving from measurements in diagnostics in the first operation of REGAE that is very close to happen  Developing diagnostic station in terms of motorizing and adding another components to complete diagnostics.

Acknowledgments H. Delsim-Hashemi1, K. Floettmann1, R. J. D. Miller2,3, M. Huening1, S.Lederer1, J. Hirscht2, D. Zhang2, G. Moriena3 1 DESY, Hamburg, Germany. 2 Max Planck Research Department for Structural Dynamics at the University of Hamburg. 3 Department of Chemistry and Physics, University of Toronto, Canada. Thanks for your attention

Experiment Magnetic lenses design How to make a diffraction image in REGAE? 4m 4m Photo cathode 1m detector target Magnetic lens 1 Magnetic lens 2 Image plane

To do: 1reading klaus KITE talk 2 cheeckingg the first solenoid 3 examining efficiency of the second inten Reading about diffraction

Simulations