14th International Particle Accelerator Conference,Venice, Italy
ISBN: 978-3-95450-231-8

ISSN: 2673-5490

JACoW Publishingdoi: 10.18429/JACoW-IPAC2023-MOPA118

R. Matsushita† , The University of Tokyo, Bunkyo-ku, Japan
H. Iinuma, K. Oda, Ibaraki University, Mito, Japan
S. Ohsawa, H. Nakayama, M. A. Rehman, K. Furukawa, N. Saito. T. Mibe
High Energy Accelerator Research Organization, Tsukuba, JapanS. Ogawa, Kyushu University, 812-8581, Fukuoka, Japan
Abstract

Demonstration Experiment ofIn the J-PARC Muon 𝑔-2/EDM experiment, to mea- Three-Dimensional Spiral Injection

sure muon anomalous magnetic moment (𝑔-2) and electrical dipole moment (EDM), it is necessary to accumulate
300 MeV/𝑐 muon beams with a 66 cm diameter region witha 3 T solenoid-type magnetic field. A new three-dimensional
spiral injection scheme has been invented to achieve this target. Since this is the first instance to employ this injection
scheme, a scale-down experiment with an electron beamof 297 keV/𝑐 and storage beam diameter of 24 cm is established at KEK. A simplified storage beam monitor using
scintillating fiber has been designed and fabricated to measure the stored beam.
The 100 ns width pulsed beam is injected and the signal
maintains a few microseconds by the stored beam observed.
According to this result, the beam storage is confirmed. The
recent result implies that the stored beam deviated from thedesign orbit and caused betatron oscillations. To measure
the beam deviation quantitatively and tune the beam, thestorage monitor has been updated. The data from this stored
beam monitor are the primary data for considering the conceptual design of the beam monitor for the muon 𝑔-2/EDM
experiment. This poster will discuss the measurement ofbeam storage by three-dimensional spiral injection and beamtuning using a scintillating fiber monitor.

In the E34 experiment, a muon beam of 300 MeV/𝑐 must
be injected and stored in a solenoid magnetic field of 3 T.
The beam storage region, which is designed to have a magnetic field uniformity of less than 0.1 ppm to surpress 𝑔-2
systematic uncertainty has a diameter of 66 cm, and a brandnew method, three-dimensional spiral injection [3], will be
employed to achieve beam storage in such a compact region.
In this technique, the beam is injected in a solenoidal magnetic field and applying vertical kick by the pulsed magnetic
field of the kicker system, able to accumulate the beam in a
weak focusing magnetic field.
Since this method is the first attempt in the world, a demonstration beamline has been constructed at KEK [4, 5]. Figure 1 shows an overview of the experimental beamline. This
demonstration experiment uses electron beams. Both thebeam momentum and the storage solenoid field strength are
scaled down from the E34: 297 keV/𝑐 and 82.5 × 10−4 T,
respectively. Under these conditions, the cyclotron radius is
12 cm and cyclotron period is 5 ns. The beam storage region
has a weak focusing magnetic field as in E34, and it 𝑛-value
is 𝑛 = 1.8 × 10−2 , two orders of magnitude stronger thanE34 for easier beam accumulation.
CCD
cameraInjection orbit

10 m

INTRODUCTION(took by DC beam)m

Storage magnet(82.5 10-4 T)

This is a preprint - the final version is published with IOP

J-PARC muon 𝑔-2/EDM Experiment
The muon anomalous magnetic moment (𝑔-2) is one ofthe physical quantities for which large discrepancies between
predictions by the Standard Model of particle physics andexperimental measurements have been reported [1]. In addition, the electric dipole moment (EDM) of elementary particles is greatly
suppressed in the Standard Model, with valuesO 10−42 𝑒 · cm. If EDM with larger values is observed, it
will be evidence of 𝐶𝑃-violation in the lepton sector. The
J-PARC muon 𝑔-2/EDM experiment (E34) [2] aims to verify
the muon 𝑔-2 anomaly and to search for muon EDM, andpreparations are underway to start physics data-taking in
JFY2028 to perform simultaneous measurements with a precision of 450 ppb for 𝑔-2 and 1.5 × 10−21 𝑒 · cm (90%C.L.)
for EDM, respectively.
∗ This work is supported by JSPS KAKENHI Grant Numbers 19H00673,

26287055, 23740216, 22K14061.

† matsur@post.kek.jp

MOPA: Monday Poster Session: MOPA
MC1.T12: Beam Injection/Extraction and Transport

XY-coupled beamcross-section(@Beam diagnostics area)

ChoppersystemRotatable
quadrupole magnet(Q1, Q2, Q3)

e-gun(80 keV)

Bendingmagnet(B1)Collimator

Bendingmagnet(B2)Beamdiagnostics
area

2m

Figure 1: An overview of the demonstration beamline. The
DC beam generated by the electron gun can be switchedby the chopper system to a pulsed beam with a pulse widthof 100 ns and a repetition rate < 50 Hz variable. The beamphase space is adjusted by three rotatable quadrupole magnets (Q1, Q2, Q3) to make an XY-coupled beam suitablefor injection [6]. The beam is deflected by the bending magnets (B1, B2) and injected into the storage magnet frombottom of the storage magnet. The kicker system is installedin the storage magnet. In the beam diagnostics area, beamdiagnostics can be performed by measuring the DC beamcross-section.
MOPA118
327

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DEMONSTRATION OF THREE-DIMENSIONAL SPIRAL INJECTION
FOR THE J-PARC MUON 𝑔-2/EDM EXPERIMENT ∗14th International Particle Accelerator Conference,Venice, Italy
ISBN: 978-3-95450-231-8

ISSN: 2673-5490

Inside of storage chamber
12 cm

Sci-FiStorageregion15 cm

Sci-Fi

17 cm

Kicker coil

Eccentric motion Tracking durationin storage plane 0ns - 1000ns

Measured signal by using Sci-Fi

Signal height [a.u.]

A single scintillation fiber (Sci-Fi) shown in Fig.2 is installed inside the storage magnet to confirm the beam accumulation by measuring the signal from stores electrons.
Here, a cylindrical coordinate system (𝑅, 𝜃, 𝑧) is used
to explain the geometrical relationship inside the storage
chamber, where 𝑅 is the distance from the center of thesolenoid magnetic field, 𝜃 is the azimuthal angle, and 𝑧 is
the position along the solenoid axis. 𝑧 = 0 cm is the storage
plane.

17 cm

Injected beam(100 ns width)Stored beam

0ns - 100ns
200ns - 300ns
400ns - 500ns
600ns - 700ns

simulation

R-position of Sci-Fi
12 cm – 0.30 cm
12 cm – 0.21 cm
12 cm
12 cm + 0.21 cm
12 cm + 0.30 cm

Time [μsec.]

Figure 3: Left: Measured signals. Injected 100 ns width
pulsed beam and applied kick in this measurement. Signal
from injected beam observed < 0.5 µs and stored beam observed > 0.5 µs. The signal from the stored beam has time
fluctuation. Right: The image of the eccentric motion of thestored beam. Horizontal- and Vertical-axis means positionon the storage plane and (𝑋, 𝑌 ) = (0, 0) means center of thesolenoid field. This eccentric motion induces fluctuation of
the measured signal.

Conceptual Design

STORAGE BEAM MONITOR
Measurement results indicate that the center of the stored
beam is estimated to be in eccentric motion. This eccentric motion broadens the 𝑅-directional distribution of thestored beam and also causes time fluctuation. The stored
beam shifts from the designed orbit causing this motion. A
storage beam monitor to measure the 𝑅-directional distribution of the stored beam and to adjust the beam based on themeasurement results is discussed.
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Support rod
(Cu)
Frame
(Al)

200 ns – 500 ns, 200 ns – 220 ns
300 ns – 320 ns, 400 ns – 420 ns
Rotating
axis(R=12 cm)

15 cm

Sci-Fi(φ200 μm)

Storage beammonitor

5.5 cmStorage beam monitor

X [m]Figure 4: Eccentric motion and storage beam monitor.
Stored beams are detected by aligning Sci-Fis with a diameter of 200 µm in the 𝑅-direction. Sci-Fis are placed at
𝑅 = 12 cm ± 0.5 cm, 12 cm ± 1 cm, 12 cm ± 2 cm, respectively. This beam monitors will be installed at two azimuth
angles, 𝜃 = ± 𝜋2 rad.
The storage beam monitor detects the beam using six
Sci-Fi arrays in the 𝑅-direction. To reduce the effect on
the stored beam, Sci-Fi with a diameter of 200 µm is usedand sparsely aligned in the 𝑅-direction. In order to performthe measurement while a kicker device (current peak: 45 A,
duration: 140 ns) is operating nearby, the light signal fromeach Sci-Fi is transmitted by optical fiber to a location far
enough outside the vacuum chamber and converted into anelectrical signal using a photodetector. Since what we wantto measure in this beam monitor is the signal derived fromthe radial oscillation of the stored beam, the 𝑧-directional
length of each Sci-Fi is set to −7.5 cm ≤ 𝑧 ≤ +7.5 cm,
which sufficiently covers the 𝑧-directional range of the beamstorage area determined from the weak focusing magnetic
field. The beam monitor is mounted on a copper support rod
that is connected to the rotary induction motor at the top of
MOPA: Monday Poster Session: MOPA
MC1.T12: Beam Injection/Extraction and TransportThis is a preprint - the final version is published with IOP

To allow measurement by changing the Sci-Fi positionin the 𝑅-direction, a rotary inductor was installed at thecenter of the port, and the Sci-Fi was attached to the tipof it with an offset of 3 mm from the rotation axis. The
𝑧-direction length of Sci-Fi (−8.5 cm ≤ 𝑧 ≤ +8.5 cm) is
sufficiently longer than the range of the beam storage region(−6 cm ≤ 𝑧 ≤ +6 cm) determined by the weak focusing
magnetic field. So, the betatron oscillation in the 𝑧-direction
does not effect the measured signal.
The signal shown on the left of Fig.3 is one of the measurement results. The stored beam-derived signal fluctuates
over time. This time fluctuation can be derived from the
𝑅-directional oscillation of the stored beam. If a beam is accumulated with an 𝑅-directional deviation from the designed
orbit, it causes eccentric motion due to the distribution of
the magnetic field in the storage region, and it generates
oscillation in the 𝑅-direction.

Beam orbit with eccentric motion]

Figure 2: Left: The chamber port at the top of the storage
chamber and single Sci-Fi using measurement. Right: Measurement setup. Sci-Fi was inserted into the beam storage
region through the port at the top of the vacuum chamber,
𝑅 = 12 cm axis.

The conceptual design of the storage beam monitor isshown in Fig.4.

[m

Beam
injection

Y

Chamber port

Z [m]Content from this work may be used under the terms of the CC BY 4.0 licence (© 2022). Any distribution of this work must maintain attribution to the author(s), title of the work, publisher, and DOI.

CONFIRMING BEAM ACCUMULATION

JACoW Publishingdoi: 10.18429/JACoW-IPAC2023-MOPA118

14th International Particle Accelerator Conference,Venice, Italy

Radial Distribution

Radial Distribution(Stored on design orbit, t=250 ns)
Azimuthsimulation(Stored on design orbit, t=450 ns)
Azimuthsimulation

Entries [-]angle+π/2 rad-π/2 rad

4

6

8

10 12

14

16

18

20

angle
+π/2 rad-π/2 rad

4

6

8

10 12

14 16 18 20

Radial Position [cm]Radial Position [cm]Radial Distribution

Radial Distribution

Expected Signal

Expected Signal(Stored on design orbit)(Stored off design orbit)

simulation

Radial position of
Sci-Fi12 cm + 0.5 cm
12 cm - 0.5 cm
12 cm + 1 cm
12 cm - 1 cm
12 cm + 2 cm
12 cm - 2 cm

Entries [-]angle+π/2 rad-π/2 radsimulation

Azimuthangle+π/2 rad-π/2 radTime [μsec.]

4

6

8

10

12

14

16

18

20

4

6

8

Radial Position [cm]

10 12

14

16

18

20

Radial Position [cm]Figure 5: Radial distribution of stored beam with time. Upper row: assuming accumulation on design orbit. Lower row:
assuming accumulation 3 cm off design orbit in 𝑅-direction.
Colors represent the azimuthal position. The distribution isstable in case of accumulation on design orbit, but off design
orbit leads to time fluctuations due to eccentric motion, andthe time fluctuates in the opposite phase at 180 deg away inthe azimuthal position.

Simulation Study
This is a preprint - the final version is published with IOP

Radial position of
Sci-Fi12 cm + 0.5 cm
12 cm - 0.5 cm
12 cm + 1 cm
12 cm - 1 cm
12 cm + 2 cm
12 cm - 2 cm

simulation(Stored off design orbit, t=450 ns)(Stored off design orbit, t=250 ns)
Azimuthsimulation

Entries [-]of Sci-Fi signals inside the beam monitor is larger than thatoutside. On the other hand, when the beam is accumulatedwith a shift of 3 cm in the 𝑅-direction. The Sci-Fi signal
inside the beam monitor is reduced and the signal outside isincreased because the distribution spreads in the 𝑅-direction
and the number of particles near the design orbit decreases.
According to this result, it is possible to put the stored
beam into the design orbit by adjusting the beam so that(Amount of inner Sci-Fi signals)/(Amount of outer Sci-Fi
signals) becomes larger. In our case, the adjustment knob
is the beam direction at the injection point, and the twomagnets installed just before the injection are used to adjust
the beam in both the 𝑥- and 𝑦-directions.

Entries [-]Entries [-]the vacuum chamber. Then, the entire storage beam monitor
can be rotated with the port center 𝑅 = 12 cm as the rotation
axis, which makes it possible to measure with a narrower
Sci-Fi spacing in practice.
This storage beam monitor will be installed at two azimuth
angles, 𝜃 = ± 𝜋2 rad. If the stored beam is in eccentric motion,√
the betatron tune in the 𝑅-direction is 1 − 𝑛 ≃ 0.99, so that
oscillations in opposite phases can be observed at two beam
monitors 180 deg apart in the azimuth position, as shownin Fig. 5.

JACoW Publishingdoi: 10.18429/JACoW-IPAC2023-MOPA118

Simulations were performed to confirm whether storage
beam monitor measurements could be used for beam tuning. In this simulation, a particle distribution with a phasespace suitable for injection (so-called XY-coupled beam)
was injected along a reference trajectory, and the hit timing
distribution to Sci-Fi at each position was confirmed fromthe motion of the stored particles, which was used as the
expected signal of the measurement. In this case, the effectof decreasing stored beam particles due to multiple scattering is not taken into account. Both cases where the beam
accumulates on the design orbit and off the design orbit were
performed.
Figure 6 shows the expected signals, where the left represents beam accumulation on the design orbit, and the right
represents accumulation 3 cm off the design orbit in the 𝑅direction. When the beam is accumulated on the design orbit,
the distribution is localized at 𝑅 = 12 cm, and the amount
MOPA: Monday Poster Session: MOPA
MC1.T12: Beam Injection/Extraction and Transport

Time [μsec.]

Figure 6: Expected signal of storage beam monitor. The left
figure shows the case where the beam is stored on the design
orbit, and the right figure shows the case where the beamis stored 3 cm off the design orbit in the 𝑅-direction. The
color difference means each Sci-Fi positions.

CONCLUSION
In the demonstration experiment of three-dimensional
spiral injection beam accumulation was successfully confirmed by measurement using Sci-Fi. From the measurement
results, it was estimated that the accumulated beams in eccentric motion because the beams were accumulated witha deviation from the designed orbit. In order to solve thiseccentricity, a beam monitor using some Sci-Fis was studied to measure the 𝑅-distribution of the stored beam andto adjust the beam. Simulation studies have shown that thestorage beam monitor can be used to adjust the beam. This
beam monitor is now under fabrication and will be installedin the first half of this fiscal year.

ACKNOWLEDGEMENTS
The author thanks H. Hisamatsu, H. Someya, T. Suwada
and Y. Yano for their general support. And this study is
supported by the Mechanical Engineering Center of KEK
Applied Research Laboratory.

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ISSN: 2673-5490

Entries [-]ISBN: 978-3-95450-231-8

14th International Particle Accelerator Conference,Venice, Italy
ISSN: 2673-5490

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JACoW Publishingdoi: 10.18429/JACoW-IPAC2023-MOPA118

for Muon 𝑔 − 2/EDM Experiment,”Ph.D.thesis, SOKENDAI,Japan, 2020. http://id.nii.ac.jp/1013/00006023/[5] R. Matsushita et al., “Development of Pulsed Beam System for
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doi:10.18429/JACoW-IPAC2021-MOPAB256[6] M. A. Rehman et al., “The First Trial of XY-Coupled Beam
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ISBN: 978-3-95450-231-8

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MC1.T12: Beam Injection/Extraction and Transport