Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 FRP042

MAGNETIC FIELD EVALUATION OF AN OCTUPOLE TYPE CERAMICSCHAMBER WITH INTEGRATED PULSED MAGNET FOR BEAMINJECTION
Y. Lu∗ , The Graduate University for Advanced Studies (SOKENDAI), [240-0193] Hayama, Japan
C. Mitsuda, H. Takaki, Y. Kobayashi, T. Uchiyama, T. Nogami
High Energy Accelerator Research Organization (KEK), [305-0801] Tsukuba, JapanAbstract
An air-core pulsed magnet named Ceramics chamber withintegrated Pulsed Magnet(CCiPM) was developed as a fast
dipole kicker at first. Because of its flexibility of the magnetic field, an octupole-like magnetic field can also be generated. A prototype of an octupole type CCiPM was fabricatedfor electron beam injection at KEK Photon Factory (KEKPF). The DC and pulsed magnetic fields of the octupole
type CCiPM were measured. Some measurement subjectsof eddy-current magnetic field evaluation and backgroundnoise treatment around zero approximate magnetic field region at the center of the magnet are discussed.

INTRODUCTION
Pulsed multipole magnet injection is being continuously
developed at KEK-Photo Factory (KEK-PF). Because of thenature of multipole magnetic field, the magnet provides astrong off-axis kick effect which kick the injection beam into
the storage ring acceptance and does not disturb the stored
beam at the center. However, the magnet is excited by anapproximate half-sinusoid current with 1.2 µs based on thephysical design [1]. Because of the eddy current effect of
the iron-core, irregular magnetic field is present at the centerand can induce the stored beam oscillation [2] .
To realize a transparent injection, air-core pulsed magnet
is a better choice for the application in future light source.
An air-core pulsed magnet named Ceramics chamber withintegrated Pulsed Magnet (CCiPM) has been developed as afast dipole kicker [3]. The CCiPM can also generate an
octupole-like magnetic field by adjusting the current direction. The cross-section view of the CCiPM with magnetic flux is shown in Fig. 1. The bore diameter is 40 mm,
and the thickness of the ceramic chamber is 10 mm. We
have proposed the design and fabricated the octupole type
CCiPM [4].
The DC and pulsed magnetic fields of the octupole type
CCiPM were measured. The measurement results are presented, and some measurement subjects of eddy-current
magnetic field evaluation and background noise treatment
around zero approximate magnetic field region at the centerof the magnet are discussed.

Figure 1: Cross-section view of the CCiPM with magneticflux.

origin of the coordinate is located at the center. Some basic
parameters of the CCiPM are summarized in Table 1.

MAGNETIC FIELD MEASUREMENT
The model of the CCiPM is shown in Fig. 2. The coordinate is marked to illustrate the measurement result. The∗ yaolu@post.kek.jp- 1019 -Figure 2: Model of the octupole type CCiPM.

Table 1: Basic Parameters of the CCiPM
ItemParameter

Total length
Length of the ceramicchamberThickness of the ceramic
Length of the coil embeddedin the ceramic
Inductance
Weight399.4 mm357.0 mm10.0 mm324.0 mm
1.45 µH<6 kg

Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 FRP042

Measurement Principle

𝑆By[T]

0.05

The DC magnetic field was measured with a Hall probe.
(F.W. Bell company, model: STF99-04-02, item number:129937). In the measurement, the current was 15 A to prevent the magnet from overheating.
As for the pulsed magnetic field, a compact pick-up probe
has been developed to measure the pulsed magnetic field precisely with a 3.2 mm × 5.8 mm coil [2]. The supplied current
was a half-sine shape current with a 0.8 µs pulse width, andthe peak value was 200 A. In the measurement, the induced
voltage 𝑉 in the coil of the probe can be expressed as∬𝑑𝜙𝑑𝑉 (𝑡) = −=− 𝑁
B · n𝑑𝑆(1)𝑑𝑡𝑑𝑡

Simulation
Normalized DC field
Normalized pulsed field

0-0.05-15-10-5051015x[mm]Figure 3: Comparison of the horizontal distribution at thecenter.

where 𝑁 is the number of turns, B is the magnetic field, n is
the normal unit vector of the area, and 𝑆 is the area of thecoil.
In the measurement, the coil is fixed to be perpendicular
to the magnetic field direction. Then the induced voltage iscalculated as∬𝑑𝑑𝑉 (𝑡) = − 𝑁
𝐵0 sin 𝜔𝑡𝑑𝑆 = − (𝐵0 𝑆𝑡𝑜𝑡 𝑎𝑙 sin 𝜔𝑡)
𝑑𝑡
𝑑𝑡

20x 10-3
Simulation
Normalized DC field
Normalized pulsed field

By[T]15105𝑆(2)where 𝐵0 is the peak pulsed magnetic field value, 𝜔 is theangular frequency of the half-sine current, and 𝑆𝑡𝑜𝑡 𝑎𝑙 is thetotal effective area. The total effective area of the probe
is 40.88 mm2 . If the voltage signal 𝑉 (𝑡) is integrated, thepeak value of the integral signal 𝐹𝑚 corresponds to the peakpulsed magnetic field which is given by
𝐵0 =𝐹𝑚𝑆𝑡𝑜𝑡 𝑎𝑙0-5-300-200-100

0200300

Figure 4: Comparison of the longitudinal distribution at𝑥=10 mm (𝑦=0 mm, −300 ≤ 𝑧 ≤ 300 mm).

(3)

1x 10-3
Simulation
Normalized DC field
Normalized pulsed field

0.5

By[T]

Measurement Results
For the convenience of comparison, the DC and pulsed
magnetic fields are normalized under the condition of a
3000 A current. Because of the narrow bore of the CCiPM
and thickness of the measurement arm, the horizontal measurement region was limited, which was from 𝑥=-12 mm to12 mm. In the measurement, the step size in the 𝑥 directionis 1 mm, and it is 2 mm in the 𝑧 direction.
The comparison of the horizontal magnetic field distribution at the center is shown in Fig. 3. The result of DC
magnetic field is almost same with the simulation data. However, the off-axis pulsed magnetic field is smaller than 20%of the simulation value.
Figure 4 shows the comparison of the longitudinal magnetic field distribution at 𝑥= 10 mm (𝑦=0 mm, −300 ≤ 𝑧 ≤300 mm). The shape of the DC magnetic field distribution isalmost same with the simulation. As for the pulsed magnetic
field, it is still less than the simulation. At 𝑧= 0mm, thesimulation value, the normalized DC magnetic field, and thenormalized pulsed magnetic field are 0.0140 T, 0.0138 T,
0.0114 T, respectively.

100z[mm]0-0.5-1-1.5
-300

-200

-100

0100

200

300

z[mm]

Figure 5: Comparison of the longitudinal distribution at
𝑥=0 mm (𝑦=0 mm, −300 ≤ 𝑧 ≤ 300 mm).
Finally, the longitudinal magnetic field distributions at
𝑥=0 mm (𝑦=0 mm, −300 ≤ 𝑧 ≤ 300 mm) are shown in
Fig. 5. Compared with the simulation, two spikes in the DCmagnetic field distribution appears around 𝑧=±150 mm. It
indicates that some undesirable magnetic components may
present in the prototype. As for the pulsed magnetic field,
there is a problem about the electromagnetic noise which- 1020 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 FRP042

cannot be removed totally in the circuit. Therefore, there
is an offset of the magnetic field at 𝑧=300 mm where theDC magnetic field is equal to zero. Although the measurement result has a systematic error, the distribution of thenormalized pulsed magnetic field is similar with that of thenormalized DC magnetic field. Two spikes also appears
around 𝑧=±150 mm, which can prove the presence of anirregular magnetic field.

ISSUES IN THE DC MAGNETIC FIELDMEASUREMENT
According to the result of the DC magnetic field, the main
problem is the undesirable magnetic field at the center. The
possible reason is discussed in this section.

Figure 7: Photograph of the arc conductor in the CCiPM.

The Kovar between the Ceramic and Flange

The Joint between the Metal Block and Coil

Because CCiPM is an air-core magnet, the magnetic field
is only generated from the current in the coil. There is nomagnetic component in the simulation model. However, thejoint between the flange and ceramic is made from Kovar,
which is a magnetic material. As shown in Fig. 6, the Kovar
is located at the end of the CCiPM. In Fig. 5, the distributionof the Normalized DC magnetic field has two spikes around𝑧=±150 mm. According to the design, the full length of theCCiPM is 400 mm, and the Kovar at one end is located at𝑧=−180 mm.
In Fig. 5, the normalized DC magnetic field at 𝑧=180 mm
is almost zero, but the spike appears at 𝑧=150 mm. Therefore,
the spike cannot be induced by the Kovar.

Figure 8 shows the CCiPM’s joint for the lead wire. The
metal block and coil are brazed together. The arc conductor
is fixed on the metal block by the bolt, which has a strong
mechanical strength. In the simulation, the current density
is assumed to be uniform in the metal block. In a real model,
the direction of the current flow and current density dependon the quality of the brazing. The position of the joint islocated at 𝑧=±145 mm, which is near the position of thespike. Therefore, the uniformity of the magnetic field may
be influenced by the joint.

Figure 8: Schematic view of the CCiPM’s joint for the leadwire.
Figure 6: Schematic view of the CCiPM.

ISSUES IN THE PULSED MAGNETIC
FIELD MEASUREMENT

Alignment and Manufacturing Errors of the ArcConductor
One element that may produce undesirable magnetic fieldis the arc conductor which is used to change the current direction. The arc conductor has manufacturing errors. Therefore,
the current flow in the arc conductor is not symmetric, andthe magnetic field at the center cannot be compensated to
be almost zero. To reduce the magnetic field error of the arc
conductor, the laser level was used to align the position of
the copper conductor. The photograph of the arc conductor is shown in Fig. 7. In addition, the arc conductor wasrandomly assembly for several times to measure the longitudinal magnetic field distribution at 𝑥=0 mm. The magnetic
field strength hardly changes. Therefore, the spike in thelongitudinal distribution is not caused by the arc conductor.

There are two issues in the pulsed magnetic field measurement. One is the off-axis magnetic field is smaller than
20% of the designed value, the other one is the accuracy ofmeasuring the magnetic field at the center.

Eddy Current Medium in the Measurement
Some eddy current mediums may have effects on thepulsed magnetic field measurement. The CCiPM is an aircore magnet, and the jig is made from resin. The conductive
components in the measurement are the titanium coating
inside the chamber and alignment stage made from stainlesssteel. According to the former simulation result, the reduction ratio of magnetic field induced by the coating is lessthan 1% [4]. Then the eddy current effect of the stainlesssteel was evaluated in the ELF/MAGIC [5].

- 1021 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 FRP042

As shown in Fig. 9, a simple model was constructed. The
vertical distance between the midplane of the CCiPM andstainless steel stage is 90 mm. Although the eddy-magnetic
field is present around the stage, the magnetic field in themidplane of the CCiPM does not change. Therefore, it isconsidered that eddy-current magnetic field does not affectthe pulsed magnetic field in the measurement.

inductance of the CCiPM, the pulse width is 0.8 µs. Owing
to the performance of the power source, the output current
is not a half-sine wave shape, It represents that the magnetic field pulse is not a half-sine wave shape. Therefore,
the calculation of the peak magnetic field is badly affected.
The result also shows that the pick-up probe is not capableof reconstructing a signal induced by an external pulsed
magnetic field whose pulse width is smaller than 1 µs. Consequently, the ringing of the current signal is the most likely
cause of the problem in the off-axis pulsed magnetic fieldmeasurement. To suppress the ringing of the current signal,
an impedance load should be added in the circuit to match
the power source.

1.2
Current signal of CT
Integrated voltage signal

Normalized value

1

Figure 9: Magnetic flux generated by the eddy current ofthe stage.

0.8
0.6
0.4
0.2
0Limitation of the Resolution Power of the Probe
The measurement precision for measuring a weak pulsed
magnetic field is limited by the resolution level of the probe.
The electromagnetic noise disturbs the measurement circuit. To reduce the noise in the measurement, the cable
was twisted together and fed into a aluminum tube that canshield against high-frequency magnetic field. However, thenoise cannot be removed totally. When the probe measured azero-magnetic field region outside the magnet, the integrated
voltage signal had a noise signal with a 1.2 nV·s maximum
amplitude, which was a systematic error in the measurement.
After calculation by Eq. 3, the noise level is 2.9 × 10−5 T.
Hence, the probe cannot measure a pulsed magnetic field
clearly whose peak value is smaller than 2.9 × 10−5 T. Afterthe normalization, the value becomes 4.4 × 10−4 T. Because
the magnetic field is too weak at the center of the CCiPM, aclear integrated voltage signal with a half-sine wave shape
was not measured at the center.

-0.2
0.5

1

1.5

2t[s]

2.5

3x 10-6Figure 10: Comparison between the CT signal and integrated
voltage signal (𝑥=12 mm, 𝑦=0 mm, 𝑧=0 mm).

CONCLUSIONThe Ringing of the Output Current Signal.

The DC and pulsed magnetic fields of the octupole type
CCiPM were measured. The DC magnetic field is almost
consistent with the simulation. However, there is a small
irregular magnetic field in the longitudinal distribution at
the center, which may increase the perturbation on the storedbeam. It is highly possible that the problem is caused by
the joint between the coil and metal block. The brazing partwill be investigated carefully in the future.

Although a noise signal with an amplitude of 1.2 nV·s
disturbed the measurement at the center, it is not likely to berelated to the off-axis magnetic field measurement. Because
at 𝑥=12 mm (𝑦=0 mm, 𝑧=0 mm), the peak value of the integrated voltage signal could reach 50 nV·s. the influence ofthe noise is less than 2.4%. In the experiment, the calculated
pulsed magnetic field is smaller than 20% of the simulation
value.
To figure out this issue, the integrated voltage signal iscompared with the current signal of the Current Transformer(CT), which is shown in Fig. 10. The CT signal is not identical to the integrated voltage signal. Because of the small

As for the pulsed magnetic field measurement, the eddycurrent magnetic field has negligible effect in the measurement. The resolution power is not enough for measuring theweak magnetic field at the center. In addition, the ringing of
the output current signal disturbs the measurement circuit
to obtain an accurate peak pulsed magnetic field value. Toimprove the current shape, the pulse width of the output
current can be expanded by adding an impedance load. Furthermore, a pulsed power source whose output current has aseveral microseconds pulse duration can be used to improve
the S/N. The main field signal is expected to be increased atthe center.

- 1022 -Proceedings of the 19th Annual Meeting of Particle Accelerator Society of Japan
October 18 - 21, 2022, Online (Kyushu University)

PASJ2022 FRP042

KEK-PF" in Proc. 17th Annual Meeting of Particle Accelerator
Society of Japan. (PASJ’2020), Japan, Sep. 2020, Online.

ACKNOWLEDGEMENTS
The author thanks the collaboration from KYOCERA Co.
This work was supported by JSPS KAKENHI Grant number
19K2649 (Representive, C.Mitsuda).

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[2] Y. Lu et al., "Evaluation of Eddy Current Effects on a Pulsed
Sextupole Magnet by a Precise Magnetic field Measurement at[3] C. Mitsuda et al., "Development of the Ceramics Chamber integrated Pulsed Magnet Fitting for a Narrow Gap" in Proc. 6thInternational Particle Accelerator Conf.(IPAC’15), Richmond,VA, USA, May. 2015, pp. 2879–2882.
[4] Y. Lu et al., "New Development of Ceramics Chamber with
Integrated Pulsed Magnet for Pulsed Multipole Injection atKEK-PF" in Proc. 18th Annual Meeting of Particle Accelerator
Society of Japan. (PASJ’2021), Japan, Sep. 2020, Online.
[5] https://www.elf.co.jp/- 1023 -