IPBSM status and plan

ATF project meetingMOroku

Schematics of Shintake Monitor

Modulation depth

Measured signal in FFTB at SLACT Shintake et al 1992y~65 nm beam size was measured

Beam Size

d fringe pitch crossing angle

Principle of Laser Interference Beam Size Monitor (Shintake Monitor)

Components of Shintake Monitor

Layout around ATF2 Interaction Point

Laser SystemQ-switched NdYAG Laser　 (wave length1064 nm)PRO350 (SpectraPhysics)

bull To make smaller interference fringe small wave length is needed second harmonics 532nm bull　 High power laser is needed to raise SN ratio 14Jpulse

Specifications Value

Wave length(second harmonics)

532 nm

Line width lt 0003 cm-1

Repetition rate 625 Hz

Pulse width 8 ns (FWHM)

Timing jitter lt 1 ns (RMS)

Pulse energy 14 Jpulse

Vertical Optical Table

Laser path diagram (174 deg crossing angle) Picture of the vertical optical table installed at ATF2 beam line

16

m

Electron Beam17 m

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Schematics of Shintake Monitor

Modulation depth

Measured signal in FFTB at SLACT Shintake et al 1992y~65 nm beam size was measured

Beam Size

d fringe pitch crossing angle

Principle of Laser Interference Beam Size Monitor (Shintake Monitor)

Components of Shintake Monitor

Layout around ATF2 Interaction Point

Laser SystemQ-switched NdYAG Laser　 (wave length1064 nm)PRO350 (SpectraPhysics)

bull To make smaller interference fringe small wave length is needed second harmonics 532nm bull　 High power laser is needed to raise SN ratio 14Jpulse

Specifications Value

Wave length(second harmonics)

532 nm

Line width lt 0003 cm-1

Repetition rate 625 Hz

Pulse width 8 ns (FWHM)

Timing jitter lt 1 ns (RMS)

Pulse energy 14 Jpulse

Vertical Optical Table

Laser path diagram (174 deg crossing angle) Picture of the vertical optical table installed at ATF2 beam line

16

m

Electron Beam17 m

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Components of Shintake Monitor

Layout around ATF2 Interaction Point

Laser SystemQ-switched NdYAG Laser　 (wave length1064 nm)PRO350 (SpectraPhysics)

bull To make smaller interference fringe small wave length is needed second harmonics 532nm bull　 High power laser is needed to raise SN ratio 14Jpulse

Specifications Value

Wave length(second harmonics)

532 nm

Line width lt 0003 cm-1

Repetition rate 625 Hz

Pulse width 8 ns (FWHM)

Timing jitter lt 1 ns (RMS)

Pulse energy 14 Jpulse

Vertical Optical Table

Laser path diagram (174 deg crossing angle) Picture of the vertical optical table installed at ATF2 beam line

16

m

Electron Beam17 m

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Laser SystemQ-switched NdYAG Laser　 (wave length1064 nm)PRO350 (SpectraPhysics)

bull To make smaller interference fringe small wave length is needed second harmonics 532nm bull　 High power laser is needed to raise SN ratio 14Jpulse

Specifications Value

Wave length(second harmonics)

532 nm

Line width lt 0003 cm-1

Repetition rate 625 Hz

Pulse width 8 ns (FWHM)

Timing jitter lt 1 ns (RMS)

Pulse energy 14 Jpulse

Vertical Optical Table

Laser path diagram (174 deg crossing angle) Picture of the vertical optical table installed at ATF2 beam line

16

m

Electron Beam17 m

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Vertical Optical Table

Laser path diagram (174 deg crossing angle) Picture of the vertical optical table installed at ATF2 beam line

16

m

Electron Beam17 m

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Switch of Laser Crossing Angle

174deg 30deg

8deg 2deg

Electron beamIssue of the Shintake Monitor 　rArr　 measurable beam size range is limited

(7 ndash 40 of fringe pitch) 　 if the fringe pitch is fixed

By changing the laser crossing angle the measurable beam size range can be enlarged

continuous

fringe pitch

crossing angle

Expected Beam Size Resolution

Expected resolution (statistical error) is evaluated by simulation considering the probable error sources

in 25 nm ～ 6 μm range less than 12 Systematic error also need to be evaluated

Simulation condition　 Statistical error of the Compton scattered photons (including background subtraction) 10　 Electron beam position jitter 30 of beam size　 Jitter of interference fringe phase 400 mrad　 Jitter of laser pulse energy 　 68　 1 measurement time 1 min　174deg 30deg 8deg 2deg

Fringe pitch

266 nm 103μm 381μm 152μm

Minimum 25 nm 100 nm 360 nm -Maximum 100 nm 360 nm - 6 μm

phase　[rad]0 2 4 6 8 10 12 14

Sign

al　Ene

rgy　　ICT

　Cha

rge　[arb

　uni

ts]

0

20

40

60

80

100

Result of continuous run

Beam conditionbull x ~ 4 cm (setting)bull y~ 1 mm (setting)

bullBG 65GeV bullSN 30

Measurement conditionbull Crossing angle ~ 796 deg = fringe pitch ~383 m

Modulation ~ 085

phase　[rad]0 2 4 6 8 10 12 14

Sign

al　Ene

rgy　　ICT

　Cha

rge　[arb

　uni

ts]

0

20

40

60

80

100

Result of continuous run

Beam conditionbull x ~ 4 cm (setting)bull y~ 1 mm (setting)

bullBG 65GeV bullSN 30

Measurement conditionbull Crossing angle ~ 796 deg = fringe pitch ~383 m

Modulation ~ 085

Sources of Systematic Error

other error sources e- beam position jittere- beam size jitterTilt of the laser fringe pattern with respect to the e- beam

phase = 2k yy [rad]0 2 4 6 8 10 12 14 16

Co

mp

ton

Sig

na

l [G

eV

]50

60

70

80

90

100

110

120

130

140

ideal modulation

Goodcontrast

fringe pattern

Poorcontrast

a error sourcedeterioration of the contrast of the laser interference fringe pattern

decrease in modulation depth

SourceMmeas Mideal

for ~300nmMmeas Mideal

for 37nm

Laser 　 power imbalance 997 997

Laser alignment accuracy gt 981 gt 981

Laser temporal coherence gt 997 gt 997

Phase jitter gt 995 995

Laser spherical wavefront ~ 100 gt 994

Beam size growth in the fringe pattern ~ 100 999

Π Factor gt 97 96

201067 10

Beam position monitor is needed Laser focal point alignment is needed Beam optics study at upper and lower IP is needed

List of Error Sources

Towards the 37nm Beam Size Measurement

In future 37nm beam size measurement following error sources cannot be neglectedLaser Spherical Wavefront

Alignment of laser focal point is needed

e- Beam Size Growth within the Fringe Pattern

We can estimate that influence from measurement of upper stream beam parameters and beam optical design

e- Beam Position Jitter

IP-BPM will enables us to correct beam position jitter in 87nm resolution (assuming 30 nm beam jitter)

With evaluation of all error sources (include statistical errors) we evaluate the Shintake monitor performance towards 37nm beam size measurement

in 1 min fringe scan

Towards the 37nm Beam Size Measurement

In future 37nm beam size measurement following error sources cannot be neglectedLaser Spherical Wavefront

Alignment of laser focal point is needed

e- Beam Size Growth within the Fringe Pattern

We can estimate that influence from measurement of upper stream beam parameters and beam optical design

e- Beam Position Jitter

IP-BPM will enables us to correct beam position jitter in 87nm resolution (assuming 30 nm beam jitter)

With evaluation of all error sources (include statistical errors) we evaluate the Shintake monitor performance towards 37nm beam size measurement

in 1 min fringe scan

Next Plan

bull Focal point scanbull Phase Monitorbull Laser position stabilization with PSDsbull (Carbon wire scanner install)bull IPBPM install (need to discuss)

focal point scan(174deg)

Mover

Mover

Stroke 30mmResolution 01m

Offset of beam position to the focal point of laser

Systematic error from spherical wavefront of laser

focal point scan(174deg)

Mover

Mover

Stroke 30mmResolution 01m

Offset of beam position to the focal point of laser

Systematic error from spherical wavefront of laser

Laser position stabilization with PSDs (1)

To monitor the drift of laser position

Put PSD at the end of long transport linedarrBetter stabilization

Plan A Plan B

Laser position stabilization with PSDs (2)

Plan to monitor the tilt of laser fringe by 2 PSDs

beam

fringe pattern

verticallongitudinal

The beam senses fringe pattern projected on transverse- and longitudinal-plane which the beam forms on

Laser position stabilization with PSDs (2)

Plan to monitor the tilt of laser fringe by 2 PSDs

beam

fringe pattern

verticallongitudinal

The beam senses fringe pattern projected on transverse- and longitudinal-plane which the beam forms on

Summary

bull Until now the measurement by 2- 8 degmode was done and systematic error sources were studied

bull The current status and the upgrade plan was reported

Backup

光路ドリフト

201067 18

気温とともに laser position がドリフト

Laser Polarization

P-polarized reflectance of the beam splitter is not 50 since the splitter is tuned for S-polarized lightSo the existence of P-polarized light causes power imbalance of the split laser beams and makes the fringe contrast worse

after polarization adjustment with half wave plate

Ps the intensity of S-polarized lightPp the intensity of P-polarized lightP the whole intensity of laser

Backup

光路ドリフト

201067 18

気温とともに laser position がドリフト

Laser Polarization

P-polarized reflectance of the beam splitter is not 50 since the splitter is tuned for S-polarized lightSo the existence of P-polarized light causes power imbalance of the split laser beams and makes the fringe contrast worse

after polarization adjustment with half wave plate

Ps the intensity of S-polarized lightPp the intensity of P-polarized lightP the whole intensity of laser

光路ドリフト

201067 18

気温とともに laser position がドリフト

Laser Polarization

P-polarized reflectance of the beam splitter is not 50 since the splitter is tuned for S-polarized lightSo the existence of P-polarized light causes power imbalance of the split laser beams and makes the fringe contrast worse

after polarization adjustment with half wave plate

Ps the intensity of S-polarized lightPp the intensity of P-polarized lightP the whole intensity of laser

Laser Polarization

P-polarized reflectance of the beam splitter is not 50 since the splitter is tuned for S-polarized lightSo the existence of P-polarized light causes power imbalance of the split laser beams and makes the fringe contrast worse

after polarization adjustment with half wave plate

Ps the intensity of S-polarized lightPp the intensity of P-polarized lightP the whole intensity of laser

distance between beam and laser laser size0 01 02 03 04 05 06 07 08 09 1

Co

ntr

as

t [

]

97

975

98

985

99

995

100

laser alignment

alignment of y-axis

alignment of z-axis

alignment accuracy

Laser Alignment Accuracy

It is important for a good contrast to align the laser pathway with beam position

Phase Jitter

Phase jitter of the laser light smears the fringe pattern and decreases modulation depthPhase jitter is caused by optical device vibrations

The Shintake monitor has a phase monitor and a light path length feedback system with piezoelectric deviceUsing the feedback system

Laser Temporal Coherence

laser spectrum(FWHM)

bull If the laser temporal coherence is poor and the two laser path lengths are different the fringe pattern contrast is reduced

bull This is because each frequency component of the laser contributes to interference in different phase under the existence of laser path length difference

Contrast Correction

Comparison with the WS measurement after Contrast correction

Magnet current [A]128 130 132 134 136 138

m]

B

ea

m s

ize

[

2

3

4

5

6

7Shintake MonitorShintake Monitor corrected

Wire Scanner

After the above corrections the measured beam size is slightly decreased but systematic shift still remains

If degrees and the Shintake monitor and the WS has comparable measurement result

Tilt of the laser fringe pattern with respect to the WS

Horizontal and longitudinal axes defined by the WS and those defined by the fringe pattern might be different

measured vertical beam size

vertical beam size

horizontal beam size

x

y

z

y

wire

fringe pattern

fringe pattern

laser size

beam

If degrees and the Shintake monitor and the WS has comparable measurement result

Tilt of the laser fringe pattern with respect to the WS

Horizontal and longitudinal axes defined by the WS and those defined by the fringe pattern might be different

measured vertical beam size

vertical beam size

horizontal beam size

x

y

z

y

wire

fringe pattern

fringe pattern

laser size

beam

Laser Spherical Wavefront

beam

fringe pattern

If beam position is away from the laser focal point when beam pass the fringe pattern beam senses courved fringe due to the laser spherical wavefront

vertical

longitudinal distance from focal point [mm]0 01 02 03 04 05 06

Co

ntr

as

t

09

092

094

096

098

1

102 x infinitesimalmx = 10

mx = 100

x horizontal beam size

Beam　Size　Growth　in　the　Fringe

Strong Focusing

Smaller Beam Size

Smaller Beta Function at IP

Beam Size Growth in the Fringe

Modulation Depth Degradationvertical

longitudinal

beam

fringe pattern

Beam　Size　Growth　in　the　Fringe

Strong Focusing

Smaller Beam Size

Smaller Beta Function at IP

Beam Size Growth in the Fringe

Modulation Depth Degradationvertical

longitudinal

beam

fringe pattern