Beam Halo Monitoring using Optical Diagnostics

Hao ZhangUniversity of Maryland/University of

Liverpool/Cockcroft Institute

Outline

• Introduction• Motivation to Study Beam Halo

• Method• Adaptive Method Using Digital Micro-mirror Device

• Experiment • University of Maryland Electron Ring (UMER)• JLAB FEL• Injection of SPEAR3 storage ring

2

• Beam Halo has many negative effects Nuclear Activation of The Transport Channel Emittance Growth Emission of Secondary Electrons Increasing Noise in The Detectors

Halo Picture credit: Kishek, Stratakis

Motivation for Beam Halo Studies

3

Halo can be regarded as small fraction of particles out a well defined beam core.

Solutions: 1) Passive spatial filtering, e.g. solar corography applied to beam imaging by T. Mitsuhashi of KEK DR = 106-107 achieved

2) Spectra-Cam CID , DR ~ 106 measured with laser by J. Egberts, C. Welsch, T. Lefevre and E. Bravin

3) Adaptive Mask based on Digital Micromirror Array; DR ~ 105 measured with laser and 8 bit CCD camera by Egberts, Welsch

Problems: 1) Need High Dynamic Range ( DR >105 - 106)

2) Core Saturation with conventional CCD’s: blooming, possible damage

3) Diffraction and scattering associated with high core intensity contaminate halo

4) Adaptability when the beam core shape change.

Imaging Halos

4

Digital Micro-mirror arrayDevice*

Micro-mirror architecture:

120

*DLPTM Texas Instruments Inc.

450

5

Mirror size: 13.68 um x 13.68 um

Resolution: 1024 X 768 pixels

Computer

MirrorSource

Halo LightCore Light

DMD

Camera Sensor

L3

L4

L1

L2Computer

Camera Sensor

L3

MirrorSource

L1

DMD

L2

L4

Image 2

Image 1Mask

Adaptive Method for Halo Measurement

6

32m

m

Quadrupole

Screen

Energy (keV) 10

Pulse width (ns) 100

Repetitive rate (Hz) 20-60

Beam current (mA) 0.6 , 6, 21,80

UMER Experiment

7

Testing filtering ability of DMD

100 200 300 400 500

100

200

300

400

500

50

100

150

200

250

8

100 200 300 400 500

100

200

300

400

500 0

1

2

3

4

5

6

x 104

Beam on, DMD all on Beam on, DMD all off

32m

m

Average readout of the core region

49616 21

20 275 1000

2000 3000

Integration Frames:

Dynamic Range Test of DMD with intense beam and circular mask*

9Integration Frames:

32m

m

Circular Mask Data line profile

10

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

70

280

xy(a)

(b)

IQ

640 660 250

45 45 60

82.9%IQ 66.3%IQ 49.7%IQQuadrupole Current

32m

m

Demonstration of Adaptive Masking on UMER

11

Bending Magnet

Energy 135 MeV

Macro pulse width: 1 ms

Repetitive rate: 60 Hz

Micro-pulse repetition rate :

4.68 MHz

Charge: 60 pc/micro pulse

Halo Experiment with OSR in JLab FEL

12

Beam pipe

1

1.2 s No mask

X

y

4 mm

4 m

m

Integration Time

3

5

2

4 62.2 s1.5 s

4 s 80 s

25000

5000

35000

15000 2000

Mask Level

Masking OSR Image of JLAB FEL Beam

13

14 s

0 200 400 600 800 100010-6

10-4

10-2

100

Pixel

Nor

mal

ized

cou

nts

1357911

Measurement of Dynamic Range for OSR DMD System

14

100

10-2

10-4

10-6

Nor

mal

ized

Coun

ts

pixel

DMA/DMD Configuration

M=4

M=1

M=0.14

More Details…

Mechanical Shutter (5ms)

Diffraction pattern

1000x1000 DMD

Filter wheelf=+125mm

f=+100mm, 2” diaScheinflug angle

9.6mM1=0.138

M2=3.55

DMDM3=1

M = M1*M2*M3 = 0.4

7.14mf=+2m

f=+125mm

f=+100mm

Aperture &Cold finger

24°PiMax

Filter wheel

OSRSource

Injector

READOUT

Gate Injected beam

Stored beam SPEAR3

Data acquisition

BTS

PSF measurement of the stored beam

0

18mm

-1-2-3-4-5-6-7

log

I /

I0

2 ms shutter mode

Increase the mask size by changing the intensity threshold level

ND filter from ND =5 to ND = 0

ND 5 ND 4 ND 3

ND 2 ND 1 ND 0

0

1

2

3

4

5

6

x 104

Mask

18 mm

No Mask

Injected beam with presence of stored beam with different currents

0 250 500 750 10001

1.5

2

2.5

x 105

Pixel

Inte

nsity

leve

l

0.42mA1.52mA3.05 mA6.11mA

(a)

0 2 4 62

3

4

5

6

Current per bucket (mA)

Inje

cted

bea

m s

ize

(mm

)

X 2*RMSY 2*RMS

(b)

6.11 mA3.05 mA1.52 mA0.42 mACurrent /bunch

Stored beamInjected beam 18 mm

Three matching condition by altering the quads in the BTS

Evolution of Beam centroid and beam size

2 4 6 8 10 12 14 16 18 20

-2

0

2

4

Turn

Bea

m Y

-cen

troi

d (m

m)

15.3 mA/min33.0 mA/min61.0 mA/min

2 4 6 8 10 12 14 16 18 201

2

3

4

Turn

2*rm

s be

am X

-siz

e (m

m)

15.3 mA/min33.0 mA/min61.0 mA/min

2 4 6 8 10 12 14 16 182

4

6

8

Turn

2*rm

s be

am Y

-siz

e (m

m)

15.3 mA/min33.0 mA/min61.0 mA/min

2 4 6 8 10 12 14 16 18 20-5

0

5

10

15

Turn

Bea

m X

-cen

troi

d (m

m)

15.3 mA/min33.0 mA/min61.0 mA/min

Conclusion

• Applied a adaptive optics to detect small image signals from either beam halo or Injected beam compared with beam core or stored beam.

• Achieve a high dynamic range with this method.

Discussion

• How can we apply this method to other existing machines?

• What is the limitation of dynamic range?• For Proton machine, since the beam is

destructive, are there any usable screens?