Proceedings of EPAC 2006, Edinburgh, Scotland

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NEW BEAM TRANSPORT LINEFROM LINAC TO PHOTON FACTORY IN KEK
N. Iida, M. Kikuchi, K. Furukawa, M. Ikeda, K. Kakihara, T. Kamitani, Y. Kobayashi, T. Mitsuhashi,
Y. Ogawa, M. Satoh, T. Suwada, M. Tawada and K. Yokoyama,KEK, 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
beam having speciﬁc energy, charge, and bunch structure.
Abstract
The 8-GeV electron LINAC in KEK injects the electron and positron beams sequentially into four storage; Low
Energy Ring(LER) of KEKB (3.5 GeV/e+ ), High Energy
Ring (HER) of KEKB (8.0 GeV/e− ), Photon Factory(PF)(2.5 GeV/e− ) and Advanced Ring for pulse X-rays(PF-AR)(3.0 GeV/e− ). The LINAC continuously injects beams
into LER and HER alternately every about ﬁve minutes,
and both of KEKB rings maintain almost full operating
currents. The PF or PF-AR needed about 20 minutes for
topping off the current, including 5 minutes for switching time of Linac, several times in a day. During this, thestored currents in KEKB rings signiﬁcantly decreased andthe optimum points of luminosity tuning was lost. It had
taken more than two hours to recover the luminosity. It istherefore important for maximizing luminosity of KEKB
to shorten the switch-time of LINAC from KEKB to PF or
PF-AR, and vice versa. In summer of 2005, the transportline from LINAC to PF were renewed, in which a new DC
bend deﬂects the electron beam from the end of LINAC
to the new line. We succeeded in reducing the occupancy
time of PF injection to about ﬁve minutes. In this paper
design of the new PF beam transport (PF/BT) line and its
performance are described.

INTRODUCTION

The thick black(red) line designates the old(new) line toPF. In the old system all beams pass through the ﬁrst bendof Energy Compression System (ECS) for KEKB/e+ and it
plays a role of switch-bend. Two KEKB beams are guided
to their own transport lines without changing ECS bend
owing to different charge and energy. Mode-change between KEKB and PF, however, needs to turn off/on theECS, simply because charge and energy are different andthe PF line is initiated at the downstream of ECS. Since theECS bends are heavily saturated it takes about three minutes for the magnetic ﬁeld to be recovered. We decided toconstruct a new line for PF where the PF beam is extracted
through the new switch-bend (BM 58 1) dedicated for PFat the upstream of ECS and guided to the existing line atdownstream of BSY. The new switch-bend is able to be set
up the magnetic condition within about a half a minute.
The new line rejoins the existing PF line at a bend, BH12.

OPTICS DESIGN
Optics parameters (β-functions, dispersion-functions
and beam sizes) from the end of LINAC to the entranceof PF ring are shown in Fig. 2. Solid and broken lines
correspond to the horizontal and vertical parameters, respectively. Fig 2-(a) and (b) show the old and new optics
respectively. The horizontal and vertical emitttances are assumed to be 1.5 × 10−8 m and 1.0 × 10−8 m respectively,
based on the measurements using wire scanners at the endof LINAC. Energy spread is assumed to be 1.25 × 10−3 .
In the new optics, β-functions are matched to those of theold optics at the lower PF/BT point where is the exit ofa bend (BH22), which is placed at the downstream of existing PF/BT line. The horizontal dispersion is also madematched to zero here. It is highly desirable to cut energy tailand beam halo at upstream of the PF/BT line. A horizontal slit is installed at a point where dispersion is larger andβ-function is smaller. Ratio of the horizontal beam sizes
originated only from dispersion to that from emittance is5.77.

COMPONENTS
Figure 1: Layout of Beam Transport Lines from LINAC

Magnets and Power Supplies

The layout of the beam-switch yard (BSY) at the end of
LINAC is shown in Fig. 1. Changing sequentially its operation mode, the Linac supplies each ring with requested

All magnets installed in the new PF/BT line can be available to 3.0 GeV beam. Bending magnets are reused fromthose of the old TRISTAN-AR beam transport (AR/BT)
line [1]. They are H-type conventional block magnets. It

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Proceedings of EPAC 2006, Edinburgh, Scotland
Table 1: Emittance growths due to jitter of bending magnets
BendBM 58 1
BM 61 F1
BM 61 F4
BH11
BH12θ (rad)0.114-0.1140.08740.131
0.131dθ/θ
10−410−410−4
10−410−4Δε/ε
4×10−3
2.2×10−2
3×10−38×10−3
1.0×10−2

BMAG
1+8×10−6
1+2×10−4
1+6×10−6
1+3×10−5
1+5×10−5

Monitors

Figure 2: Optics from the end of LINAC to the injection
point of PF.
takes about a half of minute to rise up/down magnetic ﬁeld
from zero to operation ﬁeld (∼0.92 T). There is, however,a remanent ﬁeld of 33 Gauss. At KEKB mode, main current of BM 58 1 is turned off and the correction coil of thismagnet is excited to 0.78 A in order to cancel the remanentﬁeld. There are two types of quadrupole magnets. Two ofupstream quads are reused from the old AR/BT line, whosebore diameter is 52 mm. The poles of these magnets wereremade to ﬁt the bore diameter of quads of PF line, which is63 mm. The two quads at downstream and all the steering
magnets are moved from the old PF/BT line.
Stabilities of the power supplies are less than 100 ppmin peak to peak (p-p), and the ripples of them less than 50ppm(p-p). We estimated effective growth of emittance due
to strength jitter of power supplies as below;  2β ∗ < dθ2 >
ε,
∼1+ε
ε
where ε and ε are emittances at the entrance and exit ofan bend, respectively. β ∗ is a β-function at the center ofthe bend. < dθ2 > is a mean squared jitter of deﬂection
angle of a power supply. The estimated values of emittance growths are summarized in Table 1, where jitters ofpower supplies are assumed to be 100 ppm and Δε = ε −ε.
BMAG is emittance growth from beta-mismatch. There isno problem for PF/BT operation for the stabilities of bends
with 100 ppm(p-p).

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As shown in Fig. 1, there are three screen monitors(SC 61 F∗), three BPMs [2] (SP 61 F∗) and one OctoPos
monitor[3] [4] (S8 61 F3). BPMs and steering magnets
are located near to quadrupole magnets for making an efﬁcient orbit correction. For getting more S/N, only electrodes of the ﬁrst BPM (SP 61 F1) do not rotate by 45◦ .
The screen monitors, SC 61 F1 and F4 are designed to observe beam size mainly from energy spreads and energy deviation. Whereas the screen SC 61 F2 is located at the position where dispersion is designed to be zero and used forobserving emittance proﬁles (See Fig. 2-(b)). OctoPos isa non-destructive monitor which is sensitive to quadrupole
component of the beam proﬁle. A wall current monitor [5]is installed, which measures the beam current at the end ofLINAC.

ALIGNMENTS
Magnets installed in the new line were aligned making
use of a laser tracker that measures the magnet position
with precision of 1 μm. The magnets were divided into
two groups; The upstream magnets from QD 61 F1 are deﬁned as “Group 1” and the other magnets as “Group 2”.
We deﬁne a right-handed coordinate system as indicated inFig. 1. The x-axis coincides with the direction of LINAC.
The measured data were least-square-ﬁtted to the design
value by using three free parameters; translation in x andy coordinate and rotation in the xy plane. The results ofmeasurements are summarized in Table 2.
Table 2: Results of the measurements(mm)
Group 1Group 2†

X
0.443-0.354

ΔX
0.023
0.096

Y-0.0250.020

ΔY0.1780.033

Z-0.020.03

ΔZ
0.030.04( † Group 2 for the level measurements )In the X-direction, it was found that Group 1 is 0.8mm
away from Group 2. This interval is so small that we corrected design values of magnet strengths. Each magnets
are settled with an error of about 100 μ m. These values
are small enough to correct beam orbit with the steering

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T12 Beam Injection/Extraction and TransportProceedings of EPAC 2006, Edinburgh, Scotland

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magnets. Levels of the magnets were measured with a leveling telescope. It was found that the ﬂoor level around theend of LINAC to BSY has a slant of 20.15 μm/m as shownin Fig. 3.

Figure 5: Measurements of beam positions and charges
from LINAC to the entrance of PF ring

Figure 3: Level measurements along the X-axis in BSY
Figure 6: Trend graph of injection ratio for PF ring

CONCLUSION AND FUTURE

Figure 4: Adjusted levels of magnets
To reconcile with this slanted ﬂoor we adjusted the levelsof magnets as Fig. 4; the level of Group 1 is ﬁt to the levelof LINAC while the downstream magnets from BY 61 F,deﬁned as Group 2 , are ﬁt to an average of QC1 and QC2levels. The resultant orbit from this alignment is able tobe corrected with BY 61 F1, BY 61 F5, VD4 and VD5.
Results of the level measurements are shown in Table 2 as
Z and Δ Z.

OPERATION
On 24/Sep/2005, injection mode was switched fromKEKB to PF and returned to KEKB again [6]. The timesummed for both ways were 2.6 minutes. It had taken 5.3
minutes in the old system. Thus the mode-switch time issuccessfully made almost half of that of old system. The
horizontal/vertical orbits and transmission from CT gun of
LINAC to the entrance of PR ring are shown in Fig. 5. The
differences of the horizontal orbits from the center of beam
pipes keep within 4 mm, and those of the vertical orbits
within 2 mm, which have no problem to transport the beam.
Possible beam loss may attributed to an energy tail. The
injection rate for PF ring surpassed more than 2 mA/sec asshown in Fig. 6, which is very good values compared tothat in the old beam line.

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T12 Beam Injection/Extraction and Transport

We reconstructed a half part of transport line from
LINAC to PF. The switch-magnet for PF/BT were installedat the upstream of ECS for faster change of the magneticﬁeld. Mode-switch time between KEKB and PF was madealmost half of that in original system. At the ﬁrst operation
the injection ratio was more than 2 mA/s. In the near future,
we will make a correction of optics-dispersion function.

REFERENCES[1] K. Ebihara et al.; “AR Injection Line of TRISTA”, KEK Internal 85-17, February 1986
[2] T. Suwada, N. Kamikubota, H. Fukuma, N. Akasaka andH. Kobayashi, “Stripline-type beam-position-monitor system
for single-bunch electron/positron beams” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Volume 440, Issue 2, 1 February 2000,Pages 307-319[3] T. Suwada, M. Satoh, and K. Furukawa, “New energy-spreadfeedback control system using nondestructive energy-spreadmonitors” Phys. Rev. ST Accel. Beams 8, 112802 (2005)[4] T. Suwada, M. Satoh, and K. Furukawa , “Nondestructive beam energy-spread monitor using multi-strip-line electrodes” Phys. Rev. ST Accel. Beams 6, 032801 (2003)[5] T. Suwada, K. Tamiya, T. Urano, H. Kobayashi and A. Asami,“New analysis and performance of a wall-current monitor”
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Volume 396, Issues 1-2,
1 September 1997, Pages 1-8[6] M. Satoh, “The KEK Linac Upgrade for the Fast Beam Mode
Switch” EPAC 2006 Poster Presentation MOPLS124

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