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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

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Adaptive optical masking method and its application to beam halo imaging

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


Imaging Halos Halo Imaging

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

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


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


2) OSR halo monitor at KEK employing Lyot Coronograph* SpectraCAM

Lyot Coronograph

beam image w/o filter

*T. Mitsuhashi, EPAC 2004 and Faraday Cup Award presentation 2004


3 adaptive mask using digital micromirror array

12 SpectraCAM0

13.8 um

3) Adaptive Mask using Digital Micromirror Array*

*DLPTM TexasInstruments 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)

Micro mirror architecture:

Segment of DMA:


Basic idea of the adaptive mask using dma
Basic Idea of the adaptive mask using DMA SpectraCAM

(4) Integrate and

Reimage Halo

(1) Image onto DMA

(2) Define “core”

(3) Generate mask

to block “core”


Optics Design Developed at UMD for Beam Imaging with DMA SpectraCAM

alignment

laser

240

lamp

target

CCD camera

magnifying

+ focusing lenses

DMA

Image of Circular Target on CCD)

Area of

DMA

32 mm

450


Mask generating algorithm
Mask Generating Algorithm SpectraCAM

Dx

CCD coordinates

DMA coordinates

1024 x 768 pixels

512x512 pixels

Y’’

y

y’

Magnify

y0’

Dy

y0

Y0”

x’

x0’

x0

x

X0”

X’’

Generate and apply Mask to DMA

Re-image beam


Beam Parameters: SpectraCAM

E = 10 keV

I = 1-100 mA

Dt = 1- 100 ns

www.umer.umd.edu


DMA Imaging Setup at IC1 SpectraCAM(first optical cross just after the gun)

DMA

ICCD

mirror

lens

view

port

lenses

mirror

mirror


Optics System and Image process SpectraCAM

32 mm

32 mm

900 Frames

180 Frames

DMA

13


Dynamic range measurement using intense beam and concentric circular masks
Dynamic Range Measurement using intense beam and concentric circular masks

(23mA beam Bias voltage: 30V Solenoid current: 7.9A)

290 pixel

20

65

140

275

530

820

32mm

1000

1150

1550

2000

2300

2600

5000

3000

3600

4300

5800

7000


Circular mask data line profile
Circular Mask Data line profile circular masks

with smoothing and background subtraction

32mm

1

15

0


Testing the filtering ability of the dma
Testing the filtering ability of the DMA circular masks

Beam on, DMA all on

Beam on, DMA all off

180 Gates 250 Gain 23mA beam 50V bias voltage 5.5A solenoid current


Comparison of images with dma and mirror
Comparison of Images with DMA and Mirror circular masks

DMA all on

(with Scheimplug compensation)

Mirror

(no compensation)

DMA all floating

(no compensation)

INormal = 61k counts

INormal = 64k counts

INormal = 59k counts

180 Gates 250 Gain

120 Gates 250 Gain

260 gates 250 Gain


Halo Measurement in RC7 circular masks

32mm

18


Core + Halo Variation by varying Quadruple Focusing at RC7 (23mA)

“Matched”

12.4%o

28.8%

32mm

19


Halo measurement (7 mA beam) (23mA)

f0

70

130

280

82.9% f0

20

45

80

360


66.3% f (23mA)0

45

85

660

49.7% f0

21

60

250



OSR-DMA Halo Imaging Experiment at JLAB FEL (23mA)

Site of OTR and OSR diagnostics experiments


Optics for OSR DMA Halo Experiment (23mA)

(Installed at FEL 8/2010 )

500 mm

Gallery optics: side view

Gallery optics: top view

Vault Optics: side view

24o

FEL Vault

ceiling

Camera

5 m PVC tube

1219 mm

DMA

OSR

Port

(2F06)

1000 mm

457 mm


Mitigation of COTR by Fourier Plane Filtering at LCLS (23mA)

COTR Calculations :250 MeV Gaussian beam(σ = 0.2mm > gl/2p)

Near Field Intensity Distribution

0.6

0.8

0.4

0.2

0

radius (mm)

Far field (Angular) Intensities

of COTR and IOTR

IOTR

COTR

0

0

1/g

2/γ

Observation angle



Optical system for spatial filtering/mitigation of COTR (23mA)

Focal plane of FI

(angular

Image plane)

Splitter with mask

Lens1,

F1=250mm

OTR target

2 F1

2F1

2F2

Sensor focused

on target, 1:1

Lens2,

F2=125mm

2F2

Sensor focused

on splitter, angular image, 1:1


Optical system for Fourier plane filtered Imaging with DMA (23mA)

Source

Plane

DMA at Focal plane of FI

(angular image plane)

L1

F1

L2

Sensor focused

on Source Plane


Limitations on Dynamic Range of DMA for Halo Imaging (23mA)

1- Ratio of Beam to Screen size

2- Beam Intensity : Nphotons/cm2

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.


Summary
Summary (23mA)

  • Successful Results

    • Adaptive mask method developed and use to measure halo of UMER

    • High dynamic range measured with real beam (~ 105)

    • Good filtering ~105

  • 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)

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