Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

THE FIRST RESULTS OF OPTICS MATCHING USING WIRE SCANNERS
FOR THE KEKB BEAM TRANSPORT LINE
Naoko Iida, Yoshihiro Funakoshi, Mitsuo Kikuchi, Kotaro Satoh, Tsuyoshi Suwada,
and Takashi Kawamoto, KEK, 1-1 Oho, Tsukuba-shi, Ibaraki-ken 305-0810, Japan
beam tunings. In this paper, the first results of beam-size
Abstract
In the beam transport lines from the injector linac to KEKBrings, four wire scanners were installed for each of positronand electron line. The vibrations and no-linearities ofthe wire holders were suppressed to be small enough forbeam size measurements. Optics matchings were made using the wire scanners. Better transmission from the linac
to the rings was obtained. By detecting shower due toBremsstrahlung near the detector, the beam sizes were successfully measured without any beam tunings dedicated forbackground.

1INTRODUCTION

In the KEKB the electrons(positrons) accelerated in thelinac up to 8GeV(3.5GeV) are transported to the main rings
through beam transport(BT) lines whose length are about
500m. At the BT, electron and positron lines have a doubledecked structure in the first part of tunnel of 350m long andfed into separated tunnel in the rest part. In order to maintain high luminosity, a well-controlled operation transportline is required for minimizing tuning time and a stable operation. A wire scanner(WS) for monitoring beam profiles
non-destructively is useful for these purposes. Beam testsof a prototype for WS have been done at KEKB injection
linac so far[1][2]. We produced improved wire scanners
as an actual model; more compact, less expensive but withsmaller wire vibrations. Especially we took care of the wire
positioning which leads directly the systematic error. In order to study this effect two prototypes with cantilever supports had been produced. One had linear guides in vacuum
which can suppress wire vibrations most effectively since
the cantilever was very short. Another had linear guideoutside the vacuum chamber. We measured the wire positioning for both of them[3]. As a result, both types werefeasible but we adopted the type with one linear guide forits easier handling in maintenance and lower cost. We installed ten wire scanners in total to the BT lines, for all ofwhich wire positionings had been measured before installation.
In the entrance of BT lines, at least three WS’s areneeded to determine beam emittance and Twiss parametersin the optics matching. For redundancy, we adopted four
wire scanners are mounted in each line. By using a photomultiplier tube(PMT) with plastic scintillator, we detected
shower occurred near the PMT due to Bremssstrahlung
emitted from the wire crossing a beam. The PMT’s wereset at a wide angle(65◦ ) to the beam lines. By this setting
beam background from the upstream was effectively shutoff and high S/N ratio was obtained without any dedicated0-7803-5573-3/99/$10.00@1999 IEEE.

measurement and optics matching in the positron BT line
are presented.

2PRODUCTION OF WIRE SCANNERS

2.1

A structure of the wire scanner

The schematic view of the wire scanner is shown in Fig. 1.
A thin thread of tungsten of 100µm in diameter is stretchedbetween three pins on the wire holder so as to form three(X,U- and Y-) wires perpendicular to the beam. The holder is
attached on one side of long shaft, while another side ofwhich is fixed, in a cantilever style, to a stainless block
mounted on the Linear Guide. The block is moved witha pulse-motor through a screw shaft. The Linear Guide
rails are tightly bolted on the thick base plate, which also
support the total weight of the mover. The holder and its
support shaft is in vacuum. The conversion ratio of rotation with pulse motor to linear motion is 4µm/pulse. The
linear motion is monitored through a potentiometer witha resolution of 50µm. The vacuum chamber has a window of stainless steel of 50µm in thickness which allows
low-energy knock-on electrons(δ-ray) to pass the window.
We detected the δ-ray at the window and also high energy
γ-rays at the downstream using a PMT(Hamamatsu/R32902) with a 40 × 50 × 10mm3 plastic scintillator.
INPotentiometer

Pulse Motor
X-wireU-wireY-wire,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

Linear Guidee+ Beame- or γ - rayScintillator
PMTFigure 1: Schematic view of the wire scanner.

2.2Measurement system of displacements ofwire holder

Since we adopted a cantilever to support the wire holder,a vibration in the direction perpendicular to linear motion
and to the beam was a serious concern. We have measured a static displacement (no-linearity) and also a vi-2108

Proceedings of the 1999 Particle Accelerator Conference, New York, 1999
bration during linear motion. The layout of measuringsystem is shown in Fig. 2. A laser displacement-meter,
KEYENCE/LC2430, was placed at the side of the wireholder. The LC2430 measures the distance from the surface
reflecting the emitted laser light, using a built-in positionsensitive detector(PSD). The resolution is 0.02µm. As areflector, we attached a block gauge with flatness of lessthan 0.1µm and with area of 30×10mm2 on the one sideof the holder. We measured the displacements for all of ten
WS’s to be installed within the area of the block gauge. Thelinear motion was monitored with a magnescale. The measurement was done without a vacuum vessel. The pulse rateof the pulse motor was 1kHz. The results were: maximum
amplitude of non-linear displacement was ±8µm in peakto-peak, maximum amplitude of vibration was ±10µm inpeak-to-peak. These are sufficiently small for the present
beam size.
Laser Displacement Meter
Gauge Block( 20 x 10 x 5 mm 3 )Magnescale

Laser Light
Head Part of Wire Scanner

Pb Shield
PMT

12.37 m12.37 mA-Wire

QF

QD

QF

QD
e+ Beam

B-WireC-Wire12.37 m
D-WireFigure 3: The arrangement of WS’s in the positron line

3.2

Beam optics in the wire scanners

The four wire scanners were placed at a regular section oflong straight, where the phase advance is π/2 for both of
the horizontal and vertical planes. At the region, there isno dispersion in the design. A- and C-(B- and D-) wirescanners were placed at the downstream of the defocusing(focusing) quadrupole magnets. A matching of Twiss
parameters to the linac was done by using all quadrupole
magnets upstream the wire scanners, under the condition
that the dispersion is to be closed and beta functions atsome points not exceed some maximum values.

3.3

KEYENCE LC2430( δ = 0.02 µm)

PSD

displacement

Figure 2: Schematic view of vibration measurement system.

3.1

ADC-D

ADC-C

ADC-B

Oscilloscope, Macintosh(via RS232C)*Laser Displacement Meter

3ADC-AOPTICS MATCHING

Arrangement of the wire scanners

The four wire scanners were placed at the downstream ofquadrupole magnets for each of the positron and electronline. The arrangement of WS’s in the positron line is shownin Fig 3. Two detectors(PMT’s with plastic scintillators)
were set for the four wire scanners: One PMT located near
the C-wire detects high energy particles emitted from wiresof ”A” and ”B”, while another PMT near the D-wire detects particles emitted from wires of ”C” and ”D”. Forelectron line, all detectors sit on in the same manner as”D” detector. The PMT was placed just downstream of thewindow with 65◦ in angle to the beam line. The detectors
were surrounded by lead shield of 66mm in thickness inall direction, while to the upstream side the thickness was166mm. The signal from PMT was put into the CAMAC
ADC/2249W, LeCroy. The data were taken by a VME system via CAMAC serial highway.

Measurement of beam sizes

The typical results of beam-size measurements are shownin Fig. 4 and 5 for electron(C-wire) and positron(A-wire)line,respectively. The horizontal axis is a position of wire
holder along the scanning direction and the vertical axis is
ADC count of the signal. We can clearly see three peaks
corresponding to the Y, U and X wires crossing the beam.
Each peak was fitted to an asymmetric Gaussian shape. Thebeam sizes√ of Y and X were obtained from peak with divided by 2. The typical S/N ratio was about 45 and 7.5for electron and positron. For A, B, C wire scanners, weobserved high S/N ratios almost independent on the beamcondition. This is because the background from beam halo
was almost completely shielded with the lead blocks of
166mm( 30 radiation length ). On the other hand, the signal from electromagnetic shower occurred at the beam pipenear the detector, which was generated by Bremsstrahlung
γ-rays from the upstream wire. Although the detector sits
at the wide angle(65◦ ), huge amount of Bremsstrahlung γrays emitted in extremely small angle gives high S/N ratio.
For D-wire scanner as shown in Fig 6, however, the PMT
detects the small δ-ray as the signal, while the backgroundcomes from the shower produced in front of the detector
by beam halo. We needed some dedicated beam tunings inorder to decrease the background.

3.4

Matching

We have made optics matching at the positron line. The
beam sizes at the four wire scanners were used to ob-2109

Proceedings of the 1999 Particle Accelerator Conference, New York, 1999

Figure 4: Typical transverse beam distributions(C-wire) inelectron line. The left, middle and right peaks correspondto Y-, U- and X-wires, respectively.

Figure 6: Transverse beam distributions of D-wire in
positron line.
Table 1: The obtained emittances and Bmag’s of positronline before and after matching.
εx [m]
Bmagx
εx ·Bmagx [m]εy [m]
Bmagy
εy ·Bmagy [m]Figure 5: Typical transverse beam distributions(A-wire) inpositron line.
tain Twiss parameters at the A-wire. In the phase space,
we can draw two ellipses, one from measured parameters(S1) and another from design ones(S2). An additionalellipse(S3) can be drawn that it circumscribes the ellipse
S1 and is similar to S2. Here Bmag means a ratio of anarea of ellipse(S3) to that of ellipse(S2). It is given by[4];Bmag = [β2 /β1 +β1 /β2 +β1 β2 (α1 /β1 −α2 /β2 )2 ]/2. The
subscripts 1 and 2 mean measured and design values, respectively. When measured twiss parameters are the sameas design ones, Bmag becomes unit. The obtained emittances and Bmag’s are summarized in Table 1. Although inthe horizontal direction Bmag was not changed so much, inthe vertical direction, it became smaller and the products ofemittance and Bmag decreased after matching. This meansthat the transmission of the transport line becomes better.

4CONCLUSION

We developed wire scanners for the BT line from the injector linac to KEKB rings. Since a cantilever support
for a wire holder was adopted for easier maintenance andlower cost, we carefully designed them to suppress vibration and non-linear motion of the wire. Bench measurements showed that they were negligibly small for beam size
measurements.
By using the wire scanners, the first trial for optics
matching in the positron line has been successfully done.

Before matching
1.09 × 10−6
1.16
1.26 × 10−6
2.58 × 10−7
6.54
1.69 × 10−6

After matching
7.30 × 10−7
1.62
1.18 × 10−6
2.33 × 10−7
2.04
4.75 × 10−7

Better transmission was obtained in the line. Emittances aswell as Twiss parameters obtained in the optics matchingprocess gave useful information for a tuning of the injector
linac.

5ACKNOWLEDGMENTS

The authors gratefully acknowledge the KEKB commissioning group who helped preparation of the measurement.

6REFERENCES[1] T. Suwada et al.:”FIRST BEAM TEST RESULT OF A
PROTOTYPE WIRE SCANNER FOR THE KEKB INJECTORE LINAC AND BT LINES”, Proceedings of the 11thSympo. on Accelerator Science and Technology, 1997, Hyougo, Japan, KEK Preprint 97-184, 1997
[2] Y. Funakoshi et al.:”BEAM TESTS OF A WIRE SCANNER
FOR THE KEKB INJECTOR LINAC AND BEAM TRANSPORT LINE”, Proceedings of the APAC98[3] N. Iida et al.:”A METHOD FOR MEASUREING VIBRATIONS IN WIRE SCANNER BEAM PROFILE MONITORS”, Proceedings of the APAC98[4] J. T. Seeman et al.:SLAC-PUB-5705 Aug. 19922110