Transverse beam size measurement

High energy micron electron beam non-invasive diagnostics based on

diffraction radiation  

G.Naumenko, A.Potylitsyn, L.Sukhikh 

Tomsk Polytechnic University

Transverse beam size measurement

=1

20

Ee=130 GeV

Existing advanced methodsSR - interferometer

Laser wire scanner

SakaiaY. Yamamoto, et.al., Review of Scientific instruments, 71,3 (2000)

H. Sakai, et.al., Phys.Rev.ST Accel.Beams

4:022801,2001.

Transition Radiation Monitor

Laser interferometer

M. Ross, et.al., 2001 IEEE Particle Accelerator Conference, Chicago, IL, 2001.

H. Sakai, et.al., Phys.Rev.ST Accel.Beams 4:022801,2001.

What about a non-invasive single bunch diagnostics?

Non invasive

Single bunch measurement

SR - interferometer yes no

Laser wire scanner yes no

Transition Radiation Monitor

no yes

Laser interferometer yes no

? yes yes

Non-invasive diagnostics based on the

Optical Diffraction Radiation

Short prehistoryStart: KEK ATF 2000

y

-15 -10 -5 0 5 10 15

PM

T /

curr

ent

0.0

0.2

0.4

0.6

0.8

1.0

2003

min

maxe

Wf

W

P. Karataev, S. Araki et.al., PRL 93, 244802 (2004)

Flat slit target

Measured ODR angular distribution

At 2004 the 10 beam size has been measured

P. Karataev S. Araki et.al, NIM B 227 (2005)

Optical diffraction radiation

For Ee1 GeV method sensitivity limit was reached for beam size 10 .

For Ee30 GeV the sensitivity decrease catastrophically.

Method limitation

S1S2

ODR method modificationBeam size measurement technique using ODR from crossing target was developed (G. Naumenko, KEK report, Nov. 2003)

Phase shift:

=it=

=i4z/

Calculated:

Interference pattern

S1

S2

min

maxe

Wf

W

Example for =2500, =5.6mradInterference pattern after the integration over a

Gaussian electron beam profile:

e= 2 e= 6

e= 10

For =0.5mcm =10mcm

=5.6 mrad

Single bunch measurement

Example:max

a

W e

max, OTRif a W W

For =0.5mcm and =60000 =3cm. is possible

is the Lorenz-factor

Beam size effect is of the order of OTR intensity, which was measured using CCD from a single bunch.

No dependence on the Lorenz-factor in far field zone

a

Problem of beams together bringing

2 212 2

2 21,

iss e sy D D s s p p

s e s

yeK x x y eE x y dx dy dx dy

R x x y

, , , , ,1

,s p D s p Dx x x y y y

a b

2 2 2 22

2 2p s p s D p D p

s p

x x y y x x y y

a b

2 pp px

2, ,y y yD D D DW E Ex y x y

2 ex 2 ex

o

Pseudo-photon reflection approach

2s sx

Bessel function

,s e sx x x

+_

Not any dependence on an electron position and beam size

Bi-prism Lens Mirrors

The same results may be shown for:

Moreover

Is a beam size measurement possible?

Frenel prismBased on Frenel lens technology

yD/R -80 -60 -40 -20 0 20 40 60 80

Wy

(arb

.un

)

0.0

0.2

0.4

0.6

0.8

1.0

2 2 2 22

2 2p s p s D p D p

s p

x x y y x x y y

a b

step < e

p pp p

p

step x xfrac

stepx

mrad,

xe=0 xe=5

Beam size measurement is possible

Phase

2, ,y y yD D D DW E Ex y x y

p

min

max

y e

y

Wf

W

Angular distribution

Beam size + beam position

e=7xe=0

yD/R -60 -40 -20 0 20 40 60

Wy

(arb

.un

)

0.0

0.2

0.4

0.6

0.8

e=7xe=5

min

max

y e

y

Wf

W

beam position

Beam size

Angular distribution

Single bunch measurement using CCD camera is possible

Near field zone effect

21

R

For E0=30 GeV, 0.5

2 1800m

011.02

R2

R

Deformation of OTR angular distribution

Effect is peculiar to radiation angular distribution. It shows itself for ODR as well as for OTR.

target

detectorV.A. Verzilov, Phys. Let. A 273 (2000) 135-140

Near field zone effect resolution

20.01

R

Example for OTR

Near field zoneFar field zone without lens

Angular distribution image

'1

0

2 ' ,b

E E r r J R r r dr

f

rr

''

here

Focus length

R

Bessel function

E'E

2' 'W E

W’

W’

Pis’ma w JETPh, 84 3 (2006) 136

Conclusion

• Beam size ODR effect of this method is of the first order in contrast to the effect of the second order for the method based on a flat slit target. A radiation intensity beam size effect comprises 2060% of OTR intensity. Single bunch measurement using CCD is possible near well as OTR measurement.

•The problem of radiation beams together bringing may be resolved using a special Frenel bi-prism.

•The near field effect problem may be resolved using optical system.

Test of ODR interference from the crossed target

Interference measured

KEK ATF extraction line

Target parameters: = 6.2mrad, a = 420m

Scheme

Only for interference test.

Not usable for beam size measurement