Test Results using Iris and Airy disc for the BPM Alignment of SCSS (SPring-8 Compact SASE Source) Prototype Accelerator

* JASRI (Japan Synchrotron Radiation Research Institute)** RIKEN

S. Matsui*, C.Zhang*, M.Yabshi*, S.Goto*, H.Kimura*, Ｓ．Ｋｏｊｉｍａ** ，and T. Shintake**

FEL machine Plan at SPrng-8 site

λ: 0.06 nm Energy : 8 GeV

length : 800mWe are making basic design of the building, now.

Contents1) SCSS prototype accelerator2) How to align BPM for FEL?3) Principle : Using Laser, Iris, and Airy disc4) Instruments:

(1) Laser, (2) BPM with Iris, (3) CCD camera5) Calculation of the center6) Test Results :

(1) Calibration between BPM and Iris, (2) Diameter and brightness of airy disc, (3)Reproducebility, (4)Fluctuation, (5) Stability, (6) Effect due to Gaussian, (7) Check of laser and Iris - airy disc system

7) Summary8) Alignment Plan of 18 BPMs for 8 GeV

Prototype Accelerator

Energy = 250 MevTotal Length = 60 m

U

D

from Ufrom D

Alignment telescope

CCD camera

Mirror

Laser

How to align the BPM on the linear line?

1) Using outside the BPMmechanical error ~ 10 μmneed HLS or wire or laser(in vacuum) or other

2) Using inside of BPMthe mechanics of sensor target for in and out

Reproducebility < several μm

This test case we choose 2). Laser and Iris-airy disc

Tolerance : ～５ μm / ５m Number of BPMs : 18

dydxcosr

)jkrexp()y,x(Eoj)Z,Y,X(EA∫∫ δ

−λ

=

Za 2

λ=FN

a : radius of IrisZ: distanceFresnel number

DiffractionRadiation from closed area (surface A)

r : distance

λπ

=2k

A= disc case=Iris

φ3mm Iris

φ2.5mm Iris

0.5m 2.5m 5m

10m

(from Iris)

Images after the Iris

5mm

7 1.4 φ2.5mm Iris

10m

0.350.7=λZa2

5mm

Iris Φ =3mm

Airy disc

Insert Iris in the BPMMeasure the Iris center

plane wave

IrisΦ= ２a

Z

Z>> a 2

λcondition ：distance

[ ]2Z/kaR)Z/kaR()R(I 1J=

２θ

２θ=1.2λ

a

Prinsiple for Masurementof ＢＰＭ Position using Iris and Airy disc

Laser light

R

Airy disc

J1: Bessel function

Instruments(1)He-Ne Laser

λ=633nm(red) Output Power=7mWBeam diameter=0.81mm (1/e2)Beam divergence = 1 mradPointing stability < 0.02 mrad

Expander 10×ND filter Laer tubeUniphase 1137P

XZ stage ×2ResolutionX: 2.5μmZ: 1.25μm

Iris

XZ stageResolutionX: 0.1μmZ: 0.1μm

Instruments(2)BPM with Iris

CavityBPM XZ

stageBPM is on this stage.

Iris controllerstage controller

(KODAK 4.2i) 1 pixel 9μm × 9μmtotal ２K × ２K～18.5mm × 18.5mmcover glass in front of CCD device is removed to reduce the interference

exposure time is adjustable mechanical shutterADC=8bit max counts=255

flame board is in the PCPC is used for Data analysis.

ND filter 1/100

Mirror

Instruments(3)CCD Camera

18.4mm

1pixel=9μm×9μm

Calculation of the center

0 2 4 6 8 100

2

4

6

8

10

H o s izo n t al pos it ion (m m )

Ver

tica

l P

osit

ion

(mm

)

1 .03 .05.07.09.011 .013 .015 .017 .0

0 2 4 6 8 100

2

4

6

8

10

H or izon t al P os it ion (m m )

Ver

tica

l P

osit

ion

(mm

)

1 .029.057.085.0113.0141.0169.0197.0225.0

0 2 4 6 8 100

2

4

6

8

10

H or izon t al P os it ion(m m )

Ver

tica

l P

osit

ion

(mm

)

1 .0

3 .0

5.0

7.0

9.0

11.0

13.0

15.0

17.0

Iris 3 insertion

Exposure time 1 sec18.5mm

after back ground subtraction after back ground subtraction

before back ground subtraction

Calculation of the Center

m6.0~CountsTotal

fwhmsolutionRe μ≈

18.4mm

Center position =

Mean value(gravity center)

Center position

0 200 400 600 800 1000 1200

0

10000

20000

30000

40000

50000

1pixel=9μm×9μmThis value is obtained by only 1 flame.(~1 sec) Improved by average

f w hm

T o t al c oun t s = 9740000

1 .8 m m

Cou

nts

V e r t ic al c hanne l num ber

Test result(1)Calibration between Cavity Center and Iris one

1)Search the center position as measuring output from cavity BPMWire : Cu 0.05mm RF: 4 to 6 GHz

2)Insert Iris and same search as 1)

Results of 3 BPMsRF center - Iris center = horizontal :2.5, -2, -0.5, μm

vertical : -43.5, -24.5, -46.5μm

Wire

Iris center is lower than the cavity center.

measurement

BPM

Iris1 Iris2 Iris3 Iris4no Iris

18mm

Iris No distance Iris diameter Airy disc diameter(Iris-ccd-camera) (design) (design)

1 19m 5.0mm 5.8mm2 16.5m 4.5 5.73 10.4 3.5 4.64 4.5 2 3.4

Iris1

0

50

100

150

200

250

300

0 4 8 12 16

Ver t i cal

no I r i sI r i s 1I r i s 2I r i s 4

Di st ance( mm)

3. 4mm

5. 7mm

Test Results (2)Diameter and brightness of Airydisc

agree with experiment

Test Results (3)Reproducebility of Iris insertion and pull

distance Iris-CCD camera =1 m

9. 155

9. 16

9. 165

9. 17

9. 175

20

20. 5

21

21. 5

22

22. 5

23

23. 5

56000 58000 60000 62000 64000

05/2

/5 1

2:00

:00

05/2

/5 1

2:30

:00

05/2

/5 1

3:00

:00

05/2

/5 1

3:30

:00

05/2

/5 1

4:00

:00

05/2

/5 1

4:30

:00

05/2

/5 1

5:00

:00

Ai r y di sc cent er ( I r i s : st op)

Hor i zont al - 1. 5Ver t i cal

Room_t empLaser - 15St _bef _BPM

BPMST_BPM- Camer aSt _si de_CCD

St age_CCD

Ti me( s) ( I nt er val = 22 sec)

Temperature

9. 15

9. 155

9. 16

9. 165

9. 17

19

19. 5

20

20. 5

21

21. 5

22

22. 5

12960 15120 17280 19440 21600

05/2

/4 3

:00:

00

05/2

/4 3

:30:

00

05/2

/4 4

:00:

00

05/2

/4 4

:30:

00

05/2

/4 5

:00:

00

05/2

/4 5

:30:

00

05/2

/4 6

:00:

00

Ai r y di sc Cent er ( I r i s: move)

Ver t i calHor i zont al - 1. 5

Room_t empLaser - 15St _bef _BPM

BPMST_BPM- Camer aSt _si de_CCD

St age_CCD

Posi

tion

(mm)

Ti me( s) ( I nt er val = 22 sec)

Insert→measure→pull~10sec

Insert→measure→measure~10sec stop

cycle : 22sec cycle : 22sec

Test Results (3)Reproducebility of Iris insertion and pull

5μm

5μm

Standard deviation of 4 times ~1 minute

0

0.002

0.004

0.006

0.008

0.01

no_Iris ＢＰＭ　１ ＢＰＭ　２ ＢＰＭ　３ ＢＰＭ　４

Stan

dard

dev

iatio

n（ｍ

ｍ）

σ xσ y

1 time: Average of centers among 10 flames ~15sec

Test Results(4)Fluctuation

• no Ｉｒｉｓ

• １４ hours

10. 84

10. 86

10. 88

10. 9

10. 92

10. 94

10. 1

10. 12

10. 14

10. 16

10. 18

10. 2

06/5

月/2

9 21

:00

06/5

月/2

9 23

:00

06/5

月/3

0 1:

00

06/5

月/3

0 3:

00

06/5

月/3

0 5:

00

06/5

月/3

0 7:

00

06/5

月/3

0 9:

00

06/5

月/3

0 11

:00

Dat aCent May29- 30

x

yx(

mm) y(mm)

t i me

Test Results(5)Stability

20μm

distance (laser - camera)~20m

Test Result(6)Effect of Gaussian (not plane wave)

- 0.8

- 0.6

- 0.4

- 0.2

0

0.2

0.4

0.6

0.8

- 0.8 - 0.6 - 0.4 - 0.2 0 0.2 0.4 0.6 0.8

BPM1(φ =5mm)BPM2(φ =4.5mm)BPM2dyBPM3(φ =3.5mm)BPM4(φ =2mm)

BPM shift (mm)Ai

ry d

isc

cent

er (

mm

)Measure the center as moving Iris

If Iris diameter is large, the effect becomes also large.

Test Result(6)Effect of Gaussian (not plane wave)

calculation results

0

20

40

60

80

100

120

140

2.5 3 3.5 4 4.51/e half-width of Gaussian beam (mm)

Shi

ft (m

icro

ns)

BPM 1@19.2 m, 5 mmBPM 2@16.8 m, 4.5 mmBPM 3@10.7 m, 3.5 mmBPM 4@4.8 m, 2 mm

Offset 300 microns No background subtraction

Test Results(7)Check of Laser and Airy disc system

Bar with target is attached to the BPMUsing alignment telescope (Taylor Hobson) measure the targetposition from the end of the accelerator

Nonlinearity of BPM2 and BPM3 (Reference : BPM1 and BPM4)

- 0.8- 0.7- 0.6- 0.5- 0.4- 0.3- 0.2- 0.1

00 2 4 6 8 10 12 14 16

dx_Telescopedx_noc_laserdx cor laser

BPM 1 BPM 2 BPM 3 BPM 4

(m)

Nonl

inea

rity(

mｍ

）

- 0.6

- 0.5

- 0.4

- 0.3

- 0.2

- 0.1

0

0.1

0 2 4 6 8 10 12 14 16

dy_Telescopedy_noc_laserdy cor laser

Nonl

inea

rity（

ｍｍ

）

(m)

BPM 4BPM 1 BPM 2 BPM 3

Horizontal position

Vertical position

don't include calibration result

Summary• It is possible to measure the position of Iris inside the BPM chamber

(diameter 20 mm) using airy disc for 20 m range.• If using red He-Ne laser, it is difficult to travel through 20mm inner

diameter for more than 30m at one time.• It is necessary to estimate the accuracy of this Iris-airy disc system.

It is necessary to get the flatness of the response in the CCD device. Defect pixels are corrected using next pixel values.

• Check by the other method is also necessary. For example, WPS, HLS, and so on.

• It is important to align the vacuum chamber so that the laser light is not blocked.

• The effect of Gaussian beam must be considered.• It is necessary to improve the reproducibility of Iris insertion and pull

out.• The fluctuation should be improved by searching the reason.

Alignment Plan of 18 BPMs for 8 GeV

BPM with Iris

Mirror

CCD Camera

He-Ne Laser

30m

1 unit : 6.3m

size of parallel lightλ=633nm(red)

distance diameter5m ~ 3 mm50m ~ 9 mm100m ~14 mm

tail part is not included