1. Electron Beam Diagnostics at REGAE
Shima Bayesteh
September 2011

2. 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

3. REGAE Layout Experiment REGAE Layout REGAE accelerator
The whole layout

4. 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

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

6. 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.

7. 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 
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 

8. Diagnostics
Detection system
How does Image Intensifier work?

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

10. 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.

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

12. 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.

13. Simulations Electron Gamma Shower EGS

14. 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

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

16. 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

17. 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

18. 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.

19. 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

20. 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

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

22. Simulations