RECENT PROGRESS OF WIRE SCANNER SYSTEMSFOR THE KEKB INJECTOR LINAC AND BEAM TRANSPORT LINES
N. Iida, Y. Funakoshi, T. Kawamoto, M. Kikuchi, T. Mimashi, T. Suwada, M.Tanaka, M. Yamauchi,KEK, Japan, S. Yoshida, Kanto Information Service Co., JapanAbstract

2

ARRANGEMENT OF WIRE SCANNER

Recent progresses of the wire scanner systems ofthe KEKB injector linac(LINAC) and beam transportlines(BT’s) are described. The number of optics matching
sections have been expanded from two to seven. The scanning time for each wire has been shortened drastically by
doing a measurement without stopping the wire. A unified
user-friendly software for wire scanner measurements has
been made. Daily measurements by using this new panel
are actually useful to watch machine conditions of LINACand BT. The wire scanners have also been used for a measurement of a beam energy distribution.

2.1

Overview of LINAC and BT

1

INTRODUCTION

The KEKB accelerator is a high luminosity e+ e− collider.
In order to maintain high luminosity, a well-controlled operation is required for minimizing tuning time and also for astable operation. The distances from an electron gun to theentrances of the KEKB rings are about 1km. A wire scanner(WS) for monitoring beam profiles non-destructively isuseful to carry beams through such long beam lines. A design of WS’s and beam tests of a prototype were reported
elsewhere[1, 2, 3]. Tangsten wires of 100µm in diameterare used. At least three WS’s are needed to determine beamemittance and Twiss parameters in the optics matching. For
redundancy, four wire scanners are mounted at each matching section. The first trial for optics matching by using
the wire scanners in the positron BT line was successfullydone[4]. We established seven such matching sections in
LINAC and BT’s. In addition, WS’s installed at large dispersion are used to measure an energy distribution.

KEK-B Injector

Detector
Matching Wires
Jarc
180˚ Turn
B-8

B-7

B-6

B-5

B-4

: Q magnets

Beam

Sector-B

C-2

C-3

C-4

B-3

C-5

B-2

C-6

B-1

C-7

A-4

C-8

A-3

1-1

A-2

1-2

Positron production target
Solenoid focusing system

A-1

1-3

1-4

1-51-6;;;;;

1-7 ;;;;;

2-1

2-32-22-4

2-6

2-7

Beam

Matching Wires
Detector
ECS

3-4

Sector-3

3-5

3-6

2-8

Sector-2

FODO

Beam

3-3

Fig. 1 and 2 show where the wire scanners are arranged. In
the matching systems, four wire scanners make one set. InLINAC, the sectors of B, C and 5 have each set. The same
wire scanners and quadrupole magnets are used for both ofelectron and positron optics measurements.
At the sector-B, the wire system is used to fit the optics
to that of J arc. The matching system at the sector-C is usedfor the optics diagnostics and correction after J arc. Optics
matching for the electron and positron beams is also done at
the end of LINAC(sector-5). Since acceptance of the junc-

Gun

Sector-1

Detector
Detector Matching Wires
dE/E Measuring Wire

3-2

Arrangement of wire scanners

Sector-A

Sector-C

3-1

2.2

LinacBCS
C-1

An electron beam is transported to the ring as follows. At
the head of LINAC(see Fig. 1), an electron gun generates
about 1nC electrons per bunch, which are accelerated up
to 1.7GeV in sector-A and sector-B and led to J arc. Theelectrons turned by six bending magnets in J arc are accelerated up to 8GeV when passing from sector-C to sector5, and enter into the BT line. The length of LINAC isabout 600m. In BT including four arcs, the electrons aretransported about 500m long to be injected into the KEKB
electron ring(HER). On the other hand, for positrons, 10nC
electrons per bunch generated at the same electron gun hit
on a target to obtain about 1.1nC positrons. The positrons
are accelerated up to 3.5GeV. At the end of LINAC, they
pass through Energy Compaction System(ECS). The electrons and positrons go different ways after the first bending
magnet of ECS. In the first 350m of BT, the two beams go
through a common tunnel, where beam lines have a doubledecked structure. After that, the beams are carried in separate beam lines to different injection points.

3-7

3-8

4-1

4-2

4-3

4-4

4-5

4-6

4-7

5-1

4-8

Sector-4

5-2

5-3

5-4

5-5

5-6

Sector-5
0

Figure 1: KEKB injector LINAC

5-7PF ring;;;;;;;;;;;;

5-8 ;;;;;;KEKB ring
100 mFigure 2: The entrance part of KEKB/BT

tion from LINAC to BT( including ECS for the positron )is narrow, optics matching is important for efficient beamtransmission. We have additional matching sections at theentrance of the electron and positron BT lines. One more
WS is equipped at each end of BT’s. We do not use those
WS’s at present yet.
When we choose locations of the four wire scanners,
we have to pay attention to betatron phase advance among
them. Too small phase advance brings bad accuracy in theoptics measurement. In BT’s, the phase advance is suitable
for the measurement since the wires are installed in 2π sections. However in LINAC, originally, four wires had beenbunched in a small phase advanced section. We moved one
wire beyond a quadrupole to keep enough phase advance.
There are two measurement points for energy spread.
One is at J arc of LINAC where the dispersion is 1m. Another measurement point is at the entrance of positron BT,
where the dispersion is 3m. At both points, the beam sizes
from energy spreads are large enough compared with thatfrom betatron.
Bremsstrahlung lights are emitted from a wire hit by abeam and produce showers everywhere at walls of beampipes. The photomultiplier tube(PMT) at 5∼10 m downstream of the wires detects the showers. The PMT’s usedin BT’s(H7195(R329-02)/Hamamatsu) are surrounded byleads 100mm thick, which shield backgrounds produced by a beam halo. We adopted small PMT’s for
LINAC(E5996(R5990-U)/Hamamatsu) with which we candecrease the amount of shield leads. This is because theleads are mounted on the same supports for other structuresand 30kg is the limit for additional components.

33.1

OPERATION

Matching system

In this section, panels of wire scanner systems which areused for daily operations are described.
First a selection panel is opened to choose a region tobe measured as shown in Fig. 3. In the next panel(Fig. 4),
beam sizes at four wires
in this region are measured. The√widths(devided by 2) of left most and right most peaksof the three in the graph show the vertical and horizontal
beam sizes, respectively. The data taking is done without
stopping the wire. With this new data taking method a measuring time has been remarkably reduced. It takes 30sec
for a wire to move a 120mm stroke with a 25Hz beam repetition. We can finish all measurements of Fig. 4 within

Figure 3: A region for optics matching is selected

Figure 4: Typical beam profiles in positron BT line.
five minutes. The vibration of a moving wire was measured with a prototype[3]. The result was ±10µm in peakto-peak which was small enough compared with the beamsize(0.5∼5mm) at LINAC and BT.
The optics calculations are done in the thirdpanel(Fig. 5). In LINAC, beams are accelerated amongwires. The emittance shrinks in the ratio of beam energy,γ(Lorentz factor). In the calculation, this effect is taken
into account by using the cavity voltages including thebeam loading.
The left part of Fig. 5 shows optics parameters as ellipses
in the phase space calculated from measured beam sizes.
The ellipses are drawn so that the distance from the ellipse
to the four pairs of lines obtained from the measured beam
sizes is minimum. The upper graph shows the horizontal
phase space and the lower shows the vertical one. The center part of this figure shows three ellipses. Two of thesedenote the measurement and the design. The third ellipse
is similar to that of the measurement with emittance multiplied by a measured BMAG[5]. They give a visual appealof the difference between measured and design optics.
The right part shows calculated optics parameters(α, β, εFigure 5: Optics calculation from measurements.

and BMAG). The β functions from the measurement along
the beam line are also shown. If the obtained BMAG values are rather bigger than unity, an optics matching is doneusing quadrupole magnets equipped on the upstream of thewire scanners. Fig. 6 shows a matched optics to the design.
The bar graph of this ﬁgure shows strength of the magnets
before matching (green, left side) and after matching( red,right side). When each strength of after matching is within
the limit of power supplies, the new values of quadrupoles
can be set.

Figure 7: Energy spread for primary electrons in J arc

Figure 6: Optics matching panel.

3.2

Energy spread measurement

Fig. 7 shows a panel for energy spread measurement of a10nC electron beam in J arc. The upper graph shows thehorizontal distribution at the wire scanner. The backgroundlevel is calculated by ﬁtting with an asymmetric gaussian
and a linear. The full width including 90% of the area atthis distribution after the background subtraction is deﬁned
as a full beam
 size. The energy spread is calculated by;
dE/E = σ 2 − εβ/η, where σ is a measured beam size,
ε and β are emittance and β function extrapolated from thenearest matching section and η is a designed dispersion.
The lower part of this panel shows trend plots of various
parameters calculated from the measured distribution, area,position, full width, energy spread, skewness and kurtosis.
We measure the optics parameters and the energy distributions at every wire scanner section everyday as possible.
All measured data are logged and the history of each parameter can be seen with a log viewer as shown in Fig. 8.

4

CONCLUSION AND FUTURE PLAN

The optics parameters(α, β, ε and BMAG) and energy
spreads are measured everyday with the wire scanner systems. The new data taking system without stopping wires
is successful in reducing time to get a beam size. The daily
measurements by using wire scanners are very useful towatch machine conditions of LINAC and BT.
In future, we will try optics matching from BT to the
KEKB rings. A wire scanner has been already installed

Figure 8: Trend of optics parameters in positron BT line.
at each end of electron and positron BT. The waist scan isneeded with varying quadrupole magnets upstream of thewire scanner. That completes an entire matching system of
LINAC to rings.

REFERENCES[1] T. Suwada et al.,”First Beam Test Result of a Prototype Wire
Scanner for the KEKB Injector LINAC and BT Lines”, Proceedings of the 11th Sympo. on Accelerator Science andTechnology, 1997, Hyougo, Japan,[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 Measuring Vibrations inWire Scanner Beam Proﬁle Monitors”, Proceedings of theAPAC98[4] N. Iida et al.,”The First Results of Optics Matching Using
Wire Scanners for the KEKB Beam Transport Line”, Proceedings of the PAC99[5] J. T. Seeman et al.,SLAC-PUB-5705 Aug. 1992