The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

MEASUREMENT OF WIRE ALIGNMENT IN ELECTRIC SEPTUM BY USINGA LASER-FOCUS DISPLACEMENT METER
Y. Arakaki, M. Tomizawa, N. Tokuda, andY. Mori
KEK, High Energy Accelerator Research Organization
1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305-0801, Japan
S. Shibuya
Sumitomo Heavy Industries, LTD, Yato 2-1-1, Nishi-Tokyo, Tokyo 188-8585, Japan
Table 1: Design parameters of the ESS for the50G- eV synchrotron
Deflection angle
0.2mradElectric field strength
6.8MV/mCathode Voltage170kVGap (wire-cathode)
25mm
Septum wire diameter
80/.1 mWire spacing
1.25 mm
Cathode length
1.5 m

Abstract
At an electrostatic septum used for slow extraction ina synchrotron, alignment of the septum wires is an
important issues. The reason for that, with pooralignment, the wire thickness seen by the beam iseffectively large, and consequently many particles hit
wires and are lost. We measured alignment of wires
fixed to a short test piece by using a laser-focus
displacement meter. The wires, 80/.1 m in diameter, arealigned with a spacing of 1.25 rom over a length of 100
mm. The measured alignment error is ± 15 /.1m.

1. Introduction
The accelerator complex of the JAERI/KEK Joint
Project comprises a 400MeV Linac, a 3-GeV, rapidcycling synchrotron, and a 50-GeV synchrotron[l]. In
the high intensity accelerators, beam loss cause harmful
issues such as radio radio-activation and radiation
damage for device. A criterion for beam loss was set tobe less than 1%, which is required radiation safety[2]. At
the slow extraction in 50-GeV, an electrostatic septum(ESS) will be used. Design parameters of the ESS islisted in Table 1. A beam tracking simulation for anextraction scheme using an third-order resonancepredicts that was the beam loss will be "'1.0%, if thediameter of septum wires is 100/.1 m [3]. The beam loss
occurs mainly when protons hit septum wires [4]. The
wires should be therefore as thin as possible, and aligned
precisely. For R&D of the ESS we fabricated a 0.7meter-long ESS, whose cross section is shown in Fig. 1[5]. The material of the yoke and cathode is stainlesssteel (SUS304), and that of the wires is tungsten-rhenium
alloy (W 97%, Re 3% ). The wire diameter is 80/.1 m, andthe spacing is 1.25 mm. Through high-voltage test, wehave achieved a voltage of 210 kV or higher with a wirecathode gap of 25 mm. Prior to the R&D ESS, in orderto establish the technique of fixing wires to the yoke , wemade a test piece. Its specification is the same as that ofthe R&D ESS except that the yoke length is 100 mm. We
have measured wire alignment at the test piece by usinga laser-focus displacement meter. The measurement andresult are described in this paper.

Fig. 1: The cross section of the R&D ESS.

2. A test piece for the ESS
The picture of a test piece is shown in Fig. 2. Seventynine wires are aligned with a spacing of 1.25 mm over alength of 100 mm. Each wire is fixed to the yoke at it's
upper and lower edges, where V-grooves are cut. A longwires wound spirally around the yoke so that the wire fit
into the grooves; then the grooves were caulked, and thewire was cut into 79 pieces. The wire tension was 400 gf
at the winding and"-300 gf after fixation.

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4.

Configuration of System

A programmable 3D-mover was used to move the laser
head. View of wire surface photographed with a CCD
camera on the monochrome display. The set up for themeasurement is shown in Fig. 4. The information of thelaser-head position is obtained from an output ofcontroller through an ADC board. The data processing iscarried out by an personal computer.

laser headmonochrom.,.e- - - .
displaycontroller

Fig 2 : Picture of the test piece.

3.

camera unit

Laser Focus Displacement Meter

Laser technique has been used to examine the surface
profile on the material in many fields, such as surface
science, medical science. We applied this technique tomeasure the alignment of the wires. Figure 3 shows theprinciple of the measurement. Semiconductor laser isused as light source, the laser passes through two half
mirrors, a collimating lens, and an objective lens, then isfocused onto the object. The laser reflected by the firsthalf mirror enters a pin hole, and detected by an opticalsensor. The objective lens is moved mechanically by thetuning fork. An LT-80 I 0/8020 (KEYENCE) is used aslaser head. The spot diameter is 2 /.1 m. In this method,
the distance to the object can be measured by detecting
the position of lens when the laser is focused. Light otherthan the laser may enter the optical sensor, this lightshould be taken as a noise. The regulation of the lightmagnitude is set to eliminate the noise.
semiconductor la<;eropti.cal sensor
I q]---p-1

pin holeCCDcameracollimating lens
objective lenstuning fork

Fig. 3: Principle of a laser-focus displacement meter.

/\DC'EXC controller

Fig. 4: Set-up for measuring the wire alignment.

5. Measurement
The laser head is run by 3D-mover with the speed of 0.1
mrnls along the beam axis. The resolution of the ADC
board is set to be 0.5 /.1 rnldigit. The distance between
laser head and the wire must be kept to be 5 mm ± 0.3
mm. The resolution of displacement in depth is 0.1 /.1 m.
The averaging number is set to be 16.
The displacement data of the wires is taken every 46 ms.
Figure 5 shows the surface of a wire, where x and y axes
indicates the direction in depth and the scanning
direction, respectively. To evaluate the wire alignment,
the top point on the surface of each wire must berecognized. A software which can calculate the top
position of each wire is written in the Visual Basic. This
program is useful when a large number of wires arealigned.
As shown in Fig. 6, a regular pattern is observed (somepoints with large x values indicate wires). This should betrace of the cutting on a fraise. Since the period of thepattern is 170 /.1 m, and the wire diameter is 80 /.1 m,wires may fall into grooves. This will make the wirealignment worse.
The wire alignment is shown in Fig. 7, where z axis isparallel to the wires. The base line (dx = 0) is determinedby method of least squares. A large displacement wasdetected at the wire No.79, it would be due tomanufacturing error at the yoke edge. The other wires-293-

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001(Nos.l-78) are aligned within ± 15 11 m. This value
contains errors coming from the roughness of the yokesurface, the movement of the 3D-mover. The accuracy ofthe 3D-mover will be measured by using a standard
straight-edge.

4020e_:!:o

6. Summary><-c-20

The alignment of wires in test piece ESS is measured
by a laser-focus displacement meter. The data taking
system has been developed. The alignment error was± 15 11 m except for a wire at an yoke end. The samemeasurement will be performed by R&D ESS whose
yoke was finished to a roughness of ""' 1 11 m.

-4010152025303540707580

wire number

7. Acknowledgment
40We thank M. Muto for his technical advice on the 3Dmover.

20e_.:!o><-c-20-40~

e:::1.
><~

W~

M~

wire number

Fig. 7: Alignment error of the wires.

-50

8. References
50100
Y (J.Lml

150200Fig. 5: Profile of a wire.

10Y (mm)[1] Y. Yamazaki, "High-Intensity Proton Accelerators
for the JAERI/KEK Joint Project", EPAC 2000
Proceedings.
[2] JHF Accelerator Design Report, KEK Report 97-16{JHF-97-10), 1998.
[3] N. Tokuda, "A Design of the Slow Extraction
System in the JHF 50-GeV Proton Synchrotron",
Proceedings of the 11th Symposium on Accelerator
Science and Technology.
[4] M. Tomizawa et al., "Design of Small Beam-Loss
Slow Extraction in a High Intensity 50-GeV
Proton Synchrotron", EPAC2000 Proceedings.
[5] S. Shibuya et al., "Development of an R&D
Electric Septum for the 50-GeV Proton Synchrotron",
EPAC 2000 Proceedings.

Fig. 6: Roughness on the surface of the yoke.

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