Real-time measurement in slow displacement of the tunnel
floor due to dynamic ground motion at the KEKB injector
linac

T. Suwada, Y. Enomoto, K. Kakihara, K. Mikawa, T. Higo,
Accelerator Laboratory, KEK, Tsukuba, Japan

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

1Introduction
•

•

•

•

•

High-precision laser-based alignment is one of the important issues in the
KEKB linac upgrade towards the Super KEK B-factory.
The implementation of the laser-based alignment started in the summer of2013, and the initial alignment finished in Jan. 2015.
A new remote sensing system is in progress to measure slow displacementof the tunnel floor due to dynamic ground motion in real time.
Based on the recent measurements, we have found that the transverse
displacements of the floor level with respect to the laser axis are notnegligibly small.
In this report, the measurement and analysis results are described in detailin slow displacement of the tunnel floor at the KEKB injector linac.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

2

KEKB linac layout and the laser-based alignment system• Two long straight sections, AB (125m) and C5 (475m) sections with independent
laser sources (He-Ne) and quadrant silicon photodiodes (QPDs).
• Two (seven) remote-controllable QPDs were installed in the summer shutdown of2014 (2015) at multiple locations just near expansion joints (e.j.) of the linac
building (see Table 1).
e- E = 1.5 GeVPrimary e- for e+ production E = 3.3 GeV

e- E = 7 GeV, e+ E = 4 GeV
M. Akemoto, et al., Prog. Theor. Exp. Phys. 2013 , 03A002.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France3

Alignment measurement scheme for girders andcomponents
z=0m

Laser
He-Ne

z = 500 m

Long-range laser-based alignment system

Initial QPD ( for reference )#1#2

Vacuum window#3
QPD

Acc. unit( for reference ) Last QPD#48............

Vacuum window• Long-range alignment system for girders (accuracy σ ~ 100μm)
The girder units can be aligned with a laser-based alignment system.
• Short-range alignment system for components (accuracy σ ~ 50μm)
The accelerator components on a girder unit are aligned with astandard laser-tracker technique.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

4

Table of new remote-controllable QPDs
1. Summary table in the locations of theremote controllable QPDs, andexpansion joints (e.j.) along theinjector linac from the laser source.
1. Some measurement results, themaximum norm (rm) of thedisplacement
vectorandthemaximum slope (sr) in the variationsin the time traces of the norm, are also
summarized depending on the QPD
locations.
reference QPDs

5(fixed reference QPD)
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, FranceDeveloped Remote-Controllable Quadrant Silicon
Photodiode (QPD)
Vacuum Chamber

D=117mm

Signal Extraction

QPD

Air Cylinder

Valve Control
Solenoid Valve• A remote-controllable QPD sensor, QPD: OSI Optoelectronics, SPOT-9D(D =10mmϕ)• Aperture D = 117 mm (effect. aperture D = 92 mm)• Actuator-based QPD driving system with a compact air cylinder and a microsolenoid valve driven by a compressed air
6
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, FranceRemote-controllable QPDs installed at SY2Beam axis
1200mm highe- beam

Laser

QPD_28REFUA

QPD_28G6DA

Laser axis
780mm highExpansion Joint

7
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
FranceFeedback control for stabilizing an injection laser
axis
y

z=0m

z = 500 m

z

x
Laser

Initial QPD

Last QPD

CCD

FB control for the injection angle of theStage controller laser axis at the optical system
Position stability Δx ≈ Δy ≈ 30 μm (1σ)
PC

Detector

PLC/ADC
Oscilloscope

Feedback for the motion control of linear stages through LAN

Stage with pico-motors for f5000 lens (Crucial for stable laser axis)••

Tsuyoshi Suwada/KEKB Injector Linac

M-562-XYZ/Newport, translational resolution 30nm/step  ~1nrad/step
The drive shaft is rotated by frictional force of piezoelectric element and thestage translates in the transverse plane.
IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

8

Time trace of a typical displacement vector @ QPD38DAy
7 Jan 2016

Laser

about a half year period
20 July 2016

d(r, θ)x
QPD

displacement vector ddifferential displacement vector• Every four hours on the hour, the basic functions provided by the server start towork in order to take a series of the displacement data for all the remote QPDs.
• The results show typical variations in a time trace of the displacement vector witha feedback control on.
• It can be seen that the displacement vector has complicatedly rotated around thelaser axis along with the growth of the vector norm in the time direction.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

9

Time traces of all the displacement vectors
norm

phase

• Norm and phase of thedisplacement vectors for all
the accelerator units withfeedback control on.
• The phase is defined by anangular range of 0-2π.
• Data taking period: 7 Jan –20 July 2016.
• Max. norm:
rmax = 0.19 - 0.88 mm• Average max. norm:<rmax> = 0.65 mm• Max. growth rate:
sr = 3.3 – 6.6 μm/day• Average max. growth rate:<sr> = 4.9 μm/day

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

10

Cross-correlation analysis between the displacement
vectors(1) <μ(i)> : average of the n-th displacement vectors dn(i) of the i-th QPD intime series with a maximum data length of N.
(2) Ck(i,j) : cross-covariance function between the n-th displacement vectors(dn(i) and dn(j)) obtained for the i-th and j-th QPDs, respectively, in timeseries with time lag of k.
(3) Rk(i,j) : cross-correlation function. Rk(i,j)=1 (-1) : strong positive (negative)correlation, Rk(i,j)=0: no correlation, k =0 (k≠ 0) stands for the cross-correlation
function at present (past) time.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France11

Cross-correlation analysis between the displacement
vectors•

Time traces in the cross-correlation function of the displacement vectors between
the reference QPD (QPD_REF28DA) and other QPDs for the accelerator units withthe feedback control on during the same term.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

12Animations in time series for the cross-correlation
analysis between the displacement vectors

3D Cross-correlation plot
Real-time measurement intime series of the crosscorrelation function
Tsuyoshi Suwada/KEKB Injector Linac

3D Displacement vectors

Real-time measurement in time seriesof the displacement vector
IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

13Summary
•

•

•

•

•

A new remote-controllable sensing system has been developed to measureslow dynamic displacements of the tunnel floor in real time at the KEKB
injector linac.
Based on the real-time measurements with the new system, we haveobserved non-negligible floor displacements due to dynamic groundmotion during a half year period since 7 January 2016.
The maximum norms in the displacement vector of the accelerator unit is0.65 mm on average. The maximum growth rates is 5 μm/day on average.
It can be seen that the cross-correlation function varies irregularly andfinely in the corresponding time trace, and however, the floor level in eachbuilding block moves coherently and integrally with each other on averagealong the entire length of the linac tunnel.
We will install more remote-controllable QPDs by following a plansequentially.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

14

Back-up files

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France15

Time traces of the displacement vectors (cont’d)•

It can be understood that the norms of the displacement vectors monotonicallyincrease (except for that of QPD REF1UA), while it can be seen that there are someincomprehensible fine structures in each time trace.
• The variations in the maximum norm (rm) of the displacement vector in each time
trace as a function of the QPD location are spread over a range of 0.19-0.88 mm
during a half year period, and the average maximum norm (⟨rm⟩) is 0.65 mm.
• The variations in the maximum growth rates (sr) in the time traces as a function of
the QPD location are spread over a range of 3.3-6.6 μm/day depending on the QPD
location, and the average maximum growth rate (⟨sr⟩) is 4.9 μm/day.
• It can be clearly seen that relatively large stepwise jump arises on 28 January 2016
in the time traces of the phase for QPD_1814DA and QPD_28REFUA. It takes
about four days in the rise time of the jump, and on the other hand, in the variationsin the norms of the displacement vector during the corresponding term are less than
0.2 mm. It could be understood that during the corresponding term the displacement
vector of the accelerator unit has rotated rather than increased in the transverse
plane.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

16

Cross-correlation analysis between the displacement
vectors (cont’d)• Each cross-correlation function varies irregularly in the corresponding time
trace, and however, the averages in the time traces decrease in the range of
R0 = 0.67 to 0.48 in accordance with the distance from the reference QPD(except for QPD REF1UA where R0 = 0.06).
• Relatively strong positive cross-correlations show high coherency on
average in dynamic displacements of the tunnel floor in the time series
along the entire length of the linac tunnel (except for QPD REF1UA).

• It should be noted that the time trace in the cross-correlation function for
QPD_REF1UA is markedly different from those in the other crosscorrelation functions. It seems for QPD_REF1UA to stand alone from theother building blocks.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

17

Cross-correlation analysis between the displacement
vectors (cont’d)
•
•

•

•

•

The 500-m-long linac building has two floors, which together constitute the
klystron gallery and the in-ground tunnel.
The linac building comprises eight building blocks that are joined to be linearlyaligned with seven expansion joints, which can absorb a certain amount of elastic
deformation caused by expansion or contraction of the building blocks.
However, residual amounts of elastic deformation may induce deformation of thebuilding blocks themselves. This may increase the displacement of the accelerator
units through displacements of the tunnel floor, triggered by the complex processes
that were mentioned previously.
In particular, it should be noted that the fiducial points created by the laser axis
can move dynamically and independently in proportion to the displacement vectorof the tunnel floor, even though the last fiducial point is strictly fixed at the last
QPD center with the feedback control on.
Therefore, the laser axis itself cannot become an entirely fixed and stable fiducial
axis as an absolute fiducial line, because it is not possible to directly stabilize
dynamic ground motion.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France18Data-taking procedure in the real-time measurement• Every four hours on the hour, the basic functions provided by the server
start to work in order to take a series of the displacement data for all the
QPDs.
• The basic functions comprise• a) feedback control for the laser axis, the end positions of the laser
axis at the last QPD are stabilized by the feedback control until thetransverse positions of the laser axis are within the allowable region of±50 μm from the center of the last QPD.
• b) actuator control for the QPD, the first upstream QPD is driven to
the central position of the laser pipe.
• c) data taking for the QPD, displacement data of the QPD arerepeatedly taken one thousand times, then average and standard
deviation are calculated by using the four output voltages alongwith the x and y displacements.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France19

Real-time measurements on dynamic floor motion• Variations of (a) the maximum norm and (b) the maximum growth rate in
the displacement vector measurements as a function of the QPD location.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France20Super
KEKB
Acceleratorcollider
The Super
KEKB: an electron-positronwith asymmetricComplexenergies
Ib =3.6A
e- E = 7 GeV

e+ E = 4 GeV
Ib =2.6A

Target Luminosity@SuperKEKB
L = 8 × 1035 cm-2s-1
40 times higher than the previous KEKB
L = 2 × 1034 cm-2s-1#1

Tsuyoshi Suwada /KEKB Injector Linac
Tsuyoshi Suwada/KEKB Injector Linac

500-m-long beam line for the laserbased alignment#2#3600-m-long injector linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

21

Injection Optical System
Optical system••

10-mW He-Ne laser
Solid and large optical table

Vacuum system••

Two scroll pumps (1000l/min)
Vacuum level ~3 [Pa]Parallel plate for translation tuning
f5000 lens for injection angle tuning
Optical table (1500×900×112tmm3)
Girder (Fe)Iron plate (1510×500×20tmm3)
Isolated floor separated from the tunnel
floor by a 100-mm gap (1510×500mm2)
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France22

Laser profiles at the initial and last QPDs

@ Exit of the optical system (z=0)
Wx ≈ Wy ≈ 29mm (4σ width)
Tsuyoshi Suwada/KEKB Injector Linac@ Last QPD (z=500m)
Wx ≈ 21.2mm(4σ width)Wy ≈ 17.8mm

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

23

10-mW He-Ne Laser delivering
W~30mm (FW)at the injection point

W~30mm (FW)at the 500m-long linac
end point

Vacuum level ~5Pa in laser pipes
with two scroll pumps (1000l/min)
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France24

Position displacement distributions of the laser axes for
500-m-long straight line

Horizontal

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
FranceVertical25Girder unit for accelerating structures
4 x S-band structures
Quade- beam
QPD

1200mm highLaser axis

780mm high
QPD

Laser pipe

Girder unit
8.44-m-longPD

基本ユニットTsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

26

Girder unit structure
(a)

9600

Girder plate

Girder plate

Girder plate

Guide rails

Guide rails

Accelerating structures(b)

Accelerating structures

Beam
Laser
Accelerator girder

Quadrant silicon Photo-Diode:QPD(c)A

Target for laser tracker

780

1200

B

A: Beam height
B: Laser height

T. Suwada, et al.,Rev. Sci. Instrum 81, 123301 (2010).
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France27

Short range component alignment on the girder
Reflectors
for laser
tracker
Accelerator
structure2
Mechanicalreference

Referencepoint
extended fromlaser PD

Girder1
Laser QPD
reference
Tsuyoshi Suwada/KEKB Injector Linac

3

Align andcheck withlaser tracker

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France28

Laser optical system – simple dioptric systemusing dioptric lenses and reflecting mirrors –Wide beam for Fresnel lens method

PBS f150

f50

He-Ne Laser
10mW (or 1mW)

BD
f300

Parallel plateTranslation along x and y axes

y f5000

Rotation around x and y axes

x

y

f300
PBS

For injection angle tuning
Narrow beam for QPD method

f1500
Red : Narrow beam, Blue : Wide beamTsuyoshi Suwada/KEKB Injector Linacx

For translation tuning

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France21500 × 900 mm
29

QPD Tests on radiation hardness

Present QPD,
OSI (SPOT-9D)
Hamamatsu~6 times rad.
hard

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France30

Cross-correlation analysis between the displacement
vectors(1) <μ(i)> : average of the n-th displacement vectors dn(i) of the i-th QPD intime series with a maximum data length of N.
(2) Ck(i,j) : cross-covariance function between the n-th displacement vectors(dn(i) and dn(j)) obtained for the i-th and j-th QPDs, respectively, in timeseries with time lag of k.
(3) Rk(i,j) : cross-correlation function. Rk(i,j)=1 (-1) : strong positive (negative)correlation, Rk(i,j)=0: no correlation, k =0 (k≠ 0) stands for the cross-correlation
function at present (past) time.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France31

Typical displacement vectors @ QPD-38DA
7 Jan 2016

about a half year period

7 Jan 201620 July 2016displacement vector

20 July 2016

differential displacement vector• Every four hours on the hour, the basic functions provided by the server start towork in order to take a series of the displacement data for all the QPDs.
• The results show typical variations in a time trace of the displacement vector
obtained for the accelerator units with the feedback control on.
• It can be seen that the displacement vector has complicatedly rotated around thelaser axis along with the growth of the vector norm in the time direction.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

32

Introduction of the Displacement vectors
Displacement vector

QPD_58DA

Differential

QPD_58DA• Variations in a time trace of the displacement vector obtained for the
QPD_58DA which is a feed-backed reference.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

33

Introduction of the Displacement vectors

QPD_11DA

QPD_11DA• Variations in a time trace of the displacement vector obtained for theaccelerator units with the feedback control on.
• It can be seen that the displacement vector has complicatedly rotatedaround the laser axis along with the growth of the vector norm in the time
direction.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

34

Introduction of the Displacement vectors(cont’d)

QPD_48DA

QPD_48DA• Variations in a time trace of the differential displacement vector obtained
for the accelerator units with the feedback control on.
• It can be seen that the displacement vector has complicatedly rotatedaround the laser axis along with the growth of the vector norm in the time
direction.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

35

QPD Location [m]QPD Location [m](a)Cross-correlation analysis between thedisplacement vectors(cont’d)(b)

QPD Location [m]•QPD Location [m]Intensity distributions in the cross-correlation function between all the QPDs in thedisplacement vector measurements of the accelerator units along the C5 straightsection obtained on (a) 15 February 2016 at 0:00 am and (b) 27 February 2016 at
8:00 am. The intensity distribution pattern in the cross-correlation function islinearly encoded by the color scale.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France36

Block diagram of a local control system
Linac control network
Monitor Control Station
Network Switch
Linux CPU
I/O 1
I/O 2
ADC

Detector Circuit
Consoleterminal
Klystron gallery

VME/OS9Linac tunnel

Local controller

Actuator
Air cylinder
Driving shaft
Laser

AC power
Micro switches

QPD
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

37

Detector circuit in the local control system
Monitor Outputs
QPD #1

2
3

Vm1
Vm2
Vm3

Detector Circuit

1
4

Vm4
I1
I2

y

I3
x

I4

Current Integrator
Current Integrator
Current Integrator
Current Integrator
Relay switch

QPD #2

V1
V2

A
D
C

V3
V4

I/O 1

Relay switch

QPD #10Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France38

Calibration procedure for the QPD
displacement to the laser axis
44x0 = -3 mm
x0 = -2 mm
x0 = -1 mm
x0 = +1 mm
x0 = +2 mm
x0 = +3 mm

3
2

2

1

1

y [mm]

x [mm]

y0 = -3 mm
y0 = -2 mm
y0 = -1 mm
y0 = +1 mm
y0 = +2 mm
y0 = +3 mm

3

0

0

-1

-1

-2

-2

-3

-3

Horizontal Calibration-4

Vertical Calibration

-4
0

100

200

300

QPD Location [m]

400

500

0

100

200

300

400

500

QPD Location [m]• Results in the horizontal calibration procedure for all the remote-controllable
QPDs. It should be noted that a laser source and the fiducial QPDs are located at z
= 0 and z = 500 m, respectively. The target positions controlled with the feedback
control are defined by x0 and y0 at z = 500 m.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

39

Laser size measurements along the linac• The beam widths were directly measured at the two fiducial
points (z=0 and z=500m).
• At other locations, they were analyzed by taking mapping dataobtained with the help of mechanically movable QPDs while
the laser beam was fixed. The mapping data were obtained bymeasuring the variations in the signal levels obtained from the
QPD depending on the transverse displacements with respect
to the fiducial line.
• The beam widths were analyzed by a least-square fitting
procedure with a two-dimensional Gaussian function for theobtained mapping data.

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France40

Reference target for component alignment on the girder

QPD
Target pedestal

Laser
Target pedestal

Tsuyoshi Suwada/KEKB Injector Linac• Special jig (mechanical arm) for
fiducialization of a tracker target.
• The jig and QPD are accurately
connected by flange-flangemechanical jointing.
IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France41

Component alignment on the girder
QPD

Laser

Tracker target
Special jig for fiducialization of
tracker target

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France42Isolated floor structure at the optical ystem

450 mmΦ

5000 mm

1750 mm

Tunnel floor

Isolated floor(Area:500x1500x1750tmm2) with a gap of 100
mm

PHC: Prestressed High-strength Concrete pile
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF,
Grenoble, France

43Mechanical jig for fiducialization of tracker target

targetAl A2024

Tsuyoshi Suwada/KEKB Injector Linac

400mm

SUS304 flange

Center of laser axis

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France44

Laser pipe with a viewing port

Laser

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France45

Support of accelerating structures

Laser

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France46

Connection between accelerating structure and Quad

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France47

Laser window

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France48

3D mechanical precision measurement
in QPD holder

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France49

Test bench in QPD setting calibration

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France50

Reinforced girder

Center support added
Leg reinforced
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France51

Ultrafine stage to stabilize the laser pointing
30nm/stepe- beam

PD

Laser
pipe

Accelerator
Girder
NewPort, Co. (M-562-XYZ )Ultra fine pico-motor stage

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France52

Laser system under operation

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France53

Quadrant Silicon Photo-Diode (QPD)
stopper
QPD sub-holder

QPD: OSI Optoelectronics

QPD sensor SPOT-9D (D=10mmϕ)

130mmϕQPD holder

signal pick-up• QPD is mounted in thecenter of a sub-holder.
• The sub-holder can standupright by rotation of a leverthrough hinge structure. The
inner diameter of the holder
is 130mmΦ.
• The QPD holder isconnected to a laser pipe
(SUS) by flange-flange
joining.

QPD target
54
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
FranceDevelopments for the laser-based alignment system
s

s

s

s

Our laser-based alignment system was first implemented at theconstruction stage in 1982; however, the high stabilization of the laserbased fiducial line has not been realized until now.
At long last, a laser line with high stabilization has been implemented
as a 500-m-long fiducial line for alignments in March 2013.
We experimentally investigated the propagation and stability
characteristics of the laser line passing through metallic pipes invacuum.
Pointing stability at the last fiducial point with the transverse
displacements of ±40 μm level in one standard deviation by applying a
feedback control was successfully obtained. This pointing stability
corresponds to an angle of ±0.08 μrad. This system is now fully
exhibiting the successful results for the high-precision alignment of theinjector linac currently in progress.
Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France55

Position stability of the laser axes at the last QPD(z=500m)

Horizontal

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble, France

Vertical56

Results of the laser size measurements along the linac• Direct beam size meas.
Δ: with CCDs at two end points• Indirect beam size meas.
: by a mapping with a
movable QPD in the x and y
directions at the middle locations,while the laser axis is fixed

Fitting function

Tsuyoshi Suwada/KEKB Injector Linac• Based on a least-square fitting procedure withstandard Gaussian laser optics, the widths
propagating along the z-axis were obtained asfollow:
Rayleigh lengths zRx ~ 308 m, zRy ~ 321 m,
Waist locations zx0 ~ 358 m, zy0 ~ 399 m,
Beam sizes at waist locations Wx0 ~ 18.8 mm, Wy0~ 18.0 m,
IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France57

Sensitivity measurements of the laser axis
at z = 500m

Horizontal

Tsuyoshi Suwada/KEKB Injector Linac

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
FranceVertical58

Stability measurements of the laser axes at z=500 m

Time traces of the horizontal and vertical
position displacements of the laser beam at
the last QPD (a) with the feedback control
on and off during 13.5 h
Tsuyoshi Suwada/KEKB Injector Linac

Time traces of the horizontal and vertical
position displacements of the laser beam at
the last QPD (b) with the feedback control
on during 8 h.

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France59

Position displacement distribution of the laser axesfor 132-m-long straight line

Horizontal

Tsuyoshi Suwada/KEKB Injector Linac

VerticalIWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France60

Expected error sources and estimations
ErrorsSystematic error

Statistical error
Tsuyoshi Suwada/KEKB Injector Linac

Source of errors

rms error (μm)

Mechanical• Mounting error of QPD• Mounting error of QPD holder• Reproducibility of QPD position
Electrical• Detection (offset) error of QPD
Laser Shape• Profile error

10
30
30

12
10

Summation (rms sum)46

Laser stability• Laser axis stability± 40

IWAA2016, 3-7 Oct., 2016 @ ESRF, Grenoble,
France61