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

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

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*

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

Lyot Coronograph

beam image w/o filter

3) Adaptive Mask using Digital Micromirror Array*

Segment of DMA:Micro mirror architecture:

13.8 um

120

*DLPTM 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)

Basic Idea of the adaptive mask using DMA

(1) Image onto DMA (2) Define “core” (3) Generate maskto block “core”

(4) Integrate and Reimage Halo

Image of Circular Target on CCD)

32 mm

Area ofDMA

450

Optics Design Developed at UMD for Beam Imaging with DMA

target

magnifying

+ focusing lenses

DMA

CCD camera

lamp

alignment

laser 240

Mask Generating Algorithm CCD coordinates

Generate and apply Mask to DMA

Magnify

x0

y

y0

x

y’

x’x0’

y0’Dx

Dy

DMA coordinates 1024 x 768 pixels512x512 pixels Y’’

X’’

Re-image beam

Y0”

X0”

Beam Parameters:

E = 10 keV

I = 1-100 mA

t = 1- 100 ns

www.umer.umd.edu

mirror

mirror

lenses

lens

mirror

DMA

ICCD

viewport

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

Optics System and Image process

180 Frames

32

mm

900 Frames

32

mm

DMA

13

Dynamic Range Measurement using intense beam and concentric circular masks

32m

m

290

pixe

l

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

20 65 140 275 530 820

1000 1150 2000 2600

3000 3600 4300 5000 5800

23001550

7000

Circular Mask Data line profile

0 50 100 150 200 250 300 350 400 450 50010

-6

10-5

10-4

10-3

10-2

10-1

100

Pixel

Nom

aliz

ed C

ount

0

1

32m

m

with smoothing and background subtraction

15

Testing the filtering ability of the DMA

100 200 300 400 500

100

200

300

400

500

50

100

150

200

250

100 200 300 400 500

100

200

300

400

500 0

1

2

3

4

5

6

x 104

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

Beam on, DMA all on Beam on, DMA all off

Comparison of Images with DMA and Mirror

100 150 200 250 300 350

150

200

250

300

350

400 0

0.2

0.4

0.6

0.8

1

200 250 300 350 400 450

250

300

350

400

450

500 0

0.2

0.4

0.6

0.8

1

DMA all on (with Scheimplug compensation)

Mirror (no compensation)

120 Gates 250 Gain 180 Gates 250 Gain

INormal = 61k counts INormal = 59k counts

100 150 200 250 300 350

250

300

350

400

450

0

0.2

0.4

0.6

0.8

1

DMA all floating(no compensation)

260 gates 250 Gain

INormal = 64k counts

32m

m

Halo Measurement in RC7

18

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

19

12.4%o

28.8%“Matched”

32m

m

20

Halo measurement (7 mA beam)

82.9% f0

f0

70 130 280

45 80 360

21

66.3% f0

49.7% f0

45 85 660

60 250

Future Prospects

OSR-DMA Halo Imaging Experiment at JLAB FEL

Site of OTR and OSR diagnostics

experiments

1000 mm

500 mm

OSRPort

(2F06)

Gallery optics: top view

1219

mm

457 mm

DMA

Camera

24o

Optics for OSR DMA Halo Experiment

(Installed at FEL 8/2010 )

Vault Optics: side view

5 m PVC tube

FEL Vaultceiling

Gallery optics: side view

0.4

Far field (Angular) Intensities of COTR and IOTR

0

2/γ

radius (mm)

COTR Calculations :250 MeV Gaussian beam (σ = 0.2mm > )

2( )eE

0 0.2 0.6 0.8

0 1/

Observation angle

2

2

( )

( ) exp ( sin / )

COTR IOTRI I f k

f k

( )e r

COTRIOTR

Near Field Intensity Distribution

Mitigation of COTR by Fourier Plane Filtering at LCLS

250 MeV, Far field Intensities

Angle [1/]

0 2 4 6 8 10

Inte

nsity

[arb

. uni

ts]

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0

COTRIOTR

Mitigation of COTR by Fourier Plane Filtering

λ=600nm

Mask

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(angularImage plane)

2F2

2F2 2F1

Optical system for Fourier plane filtered Imaging with DMA

SourcePlane

L2

Sensor focused on Source Plane

DMA at Focal plane of FI (angular image plane)

L1

F1

Limitations on Dynamic Range of DMA for Halo Imaging

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 • 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)

30