1. Adaptive Optical Masking Method and Its Application to Beam Halo Imaging Ralph Fiorito H. Zhang, A. Shkvarunets, I. Haber, S. Bernal, R. Kishek, P. O’Shea Institute for Research in Electronics and Applied Physics, University of Maryland S. Artikova MPI- Heidelberg C. Welsch Cockcroft Institute, University of Liverpool

2. Outline Introduction Beam Halo Imaging Problems and Solutions to date New Halo Imaging Method using DMA -DMA Properties -Imaging Optics developed at UMD -Test Results with UMER electron beam -Current Problems/Solutions of DMA Halo Imaging -Future Prospects for DMA Halo Imaging

3. Imaging Halos Solutions: 1) High Dynamic Range CID Camera (Spectra-Cam), DR ~ 10(6) measured with laser by J. Egberts, et, al. MPI-Heidelberg 2) Spatial filtering a) Fixed mask (solar coronagraphy applied to beams) DR = 10(6) -10(7) beamcore to halo intensity observed by Mitsuhashi (KEK) b) Adaptive Mask based on Digital Micromirror Array; DR ~ 10(5) measured with laser and 8 bit CCD by Egberts, Welsch Problems: 1) Need High Dynamic Range ( DR >10(5) - 10(6) ) 2) Core Saturation with conventional CCD’s: blooming, possible damage 3) Diffraction and scattering associated with high core intensity - contaminates halo image

4. 1) High Dynamic Range CID Camera: Thermo Scientific SpectraCAM Features: 1- Non destructive read out 2- DR (advertised): 28 bit; DR > 10(5) measured with laser* 3- CID: greater radiation hardness than CCD 4- High cost > $25K *C.Welsch, E.Bravin and T.Lefevre Proc.SPIE 2007

5. 2) OSR halo monitor at KEK employing Lyot Coronograph* *T. Mitsuhashi, EPAC 2004 and Faraday Cup Award presentation 2004 Lyot Coronograph beam image w/o filter

6. 3) Adaptive Mask using Digital Micromirror Array * Segment of DMA: Micro mirror architecture: 13.8 um 12 0 *DLP TM Texas Instruments Inc. 1024 x 768 pixels (XGA) [ Discovery 1100]  USB Interface  high-speed port 64-bit @ 120 MHz for data transfer  up to 9.600 full array mirror patterns / sec (7.6 Gbs)

7. Basic Idea of the adaptive mask using DMA (1) Image onto DMA(2) Define “core”(3) Generate mask to block “core” (4) Integrate and Reimage Halo

8. Considerations for Designing Imaging Optics using DMA 1.DMA micromirrors have three possible states: 1- all floating, nominally flat state (power off) 2- two individually addressable + - 12 0 states (power on) 2.Rotation axis along diagonal of each micromirror, i.e. at 45 degrees wrt to DMA row or column 1+2 mean that rays imaged onto the DMA plane are reflected with different optical path lengths at twice the angle of incidence (e.g. +24 0) 3.Diffraction effects: array acts like a 2D grating producing cross like diffraction pattern

9. Image of Circular Target on CCD) 32 mm Area of DMA 45 0 Optics Design Developed at UMD for Beam Imaging with DMA target magnifying + focusing lenses DMA CCD camera lamp alignment laser 24 0

10. Mask Generating Algorithm CCD coordinates Generate and apply Mask to DMA Magnify x0x0 y y0y0 x y’ x’ x0’x0’ y0’y0’ Dx Dy DMA coordinates 1024 x 768 pixels 512x512 pixels Y’’ X’’ Re-image beam Y0”Y0” X0”X0”

11. Beam Parameters: E = 10 keV I = 1-100 mA  t = 1- 100 ns www.umer.umd.edu

12. mirror lenses lens mirror DMA ICCD view port DMA Imaging Setup at IC1 (first optical cross just after the gun)

13. Optics System and Image process 180 Frames 32 mm 900 Frames 32 mm DMA 13

14. Dynamic Range Measurement using intense beam and concentric circular masks 32mm 290 pixel (23mA beam Bias voltage: 30V Solenoid current: 7.9A) 2065140275530820 1000115020002600 300036004300 5000 5800 23001550 7000

15. Circular Mask Data line profile 0 1 32mm with smoothing and background subtraction 15

16. Testing the filtering ability of the DMA 180 Gates 250 Gain 23mA beam 50V bias voltage 5.5A solenoid current Beam on, DMA all onBeam on, DMA all off

17. Comparison of Images with DMA and Mirror DMA all on (with Scheimplug compensation) Mirror (no compensation) 120 Gates 250 Gain 180 Gates 250 Gain I Normal = 61k counts I Normal = 59k counts DMA all floating (no compensation) 260 gates 250 Gain I Normal = 64k counts

18. 32mm Halo Measurement in RC7 18

19. Core + Halo Variation by varying Quadruple Focusing at RC7 (23mA) 19 12.4% o 28.8%“Matched” 32mm

20. 20 Halo measurement (7 mA beam) 82.9% f 0 f0f0 70130280 4580360

21. 21 66.3% f 0 49.7% f 0 4585660 60250

22. Future Prospects

23. OSR-DMA Halo Imaging Experiment at JLAB FEL Site of OTR and OSR diagnostics experiments

24. 1000 mm 500 mm OSR Port (2F06) Gallery optics: top view 1219 mm 457 mm DMA Camera 24 o Optics for OSR DMA Halo Experiment (Installed at FEL 8/2010 ) Vault Optics: side view 5 m PVC tube FEL Vault ceiling Gallery optics: side view

25. 0.4 Far field (Angular) Intensities of COTR and IOTR 0 2/γ radius (mm) COTR Calculations :250 MeV Gaussian beam (σ = 0.2mm >  ) 0 0.2 0.60.8 0 1/  Observation angle COTR IOTR Near Field Intensity Distribution Mitigation of COTR by Fourier Plane Filtering at LCLS

26. Mitigation of COTR by Fourier Plane Filtering λ=600nm Mask

27. Optical system for spatial filtering/mitigation of COTR OTR target Lens1, F1=250mm Lens2, F2=125mm Splitter with mask Sensor focused on target, 1:1 Sensor focused on splitter, angular image, 1:1 2 F1 Focal plane of FI (angular Image plane) 2F2 2F1

28. Optical system for Fourier plane filtered Imaging with DMA Source Plane L2 Sensor focused on Source Plane DMA at Focal plane of FI (angular image plane) L1 F1

29. Limitations on Dynamic Range of DMA for Halo Imaging 1- Ratio of Beam to Screen size 2- Beam Intensity : N photons /cm 2 3- Photon Yield of Screen 4- Dynamic Range of Screen itself (saturation, linearity) 5- Light scattering/diffraction in optics 6- Integration time for halo measurement (beam stability issue) Possible solutions: 1- Higher beam intensity + attenuators 2- Higher DR/linearity “screens” e.g. OTR, OSR, OER 3- Improved optics: polarizers, Lyot stops, etc.

30. Summary Successful Results – Adaptive mask method developed and use to measure halo of UMER – High dynamic range measured with real beam (~ 10 5 ) – Good filtering ~10 5 Limitations on dynamic range – Beam intensity – Screen property: efficiency, saturation – Scattered light Possible solution – higher intensity beam (other accelerators ) – More efficient screen, e.g. YAG, or use of OSR, OUR etc. – improve optics (polarizer, Lyot stops) Future prospects – Study halo propagation in the first turn in the UMER ring – Experiments at other facilities (JLAB, SLAC/LCLS,SPEAR3) 30