Proceedings of the 18th Annual Meeting of Particle Accelerator Society of Japan
August 9 - 11, 2021, Takasaki, Japan

PASJ2021 MOOB03

NEW DEVELOPMENT OF CERAMICS CHAMBER WITH INTEGRATEDPULSED MAGNET FOR PULSED MULTIPOLE INJECTION AT KEK-PF
Y. Lu∗ , The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
C. Mitsuda, H. Takaki, T. Obina, K. Harada, R. Takai, Y. Kobayashi, T. Nogami,
T. Uchiyama, High Energy Accelerator Research Organization (KEK), Tsukuba, JapanAbstract
The KEK-PF is now dedicated to the development ofpulsed multipole injection scheme. An experiment of pulsed
sextupole injection has been performed successfully. Although this method could inject a beam into the storage
ring without large perturbation, the stored beam is still disturbed due to eddy current effects of iron core magnet andcoating inside of the chamber. To suppress the perturbation completely, Ceramics Chamber with integrated Pulsed
Magnet(CCiPM) of an air-core magnet, which is developed
specially as fast pulsed kicker, is being expanded to multipole pulsed magnet, which could generate an Octupole-likemagnetic field. To examine the performance of Octupoletype CCiPM, some preliminary experiments are conducted
such as durability test, current excitation test and magnetic
field measurement to evaluate the mechanical performanceand magnetic field quality. The design and experimental
results will be reviewed.

beam size. To suppress eddy current effect completely, aircore pulsed magnet must be developed to replace iron-core
pulsed magnet.

CERAMICS CHAMBER WITH
INTEGRATED PULSED MAGNET
introduction
The Ceramics Chamber with integrated Pulsed Magnet(CCiPM) is developed by C. Mitsuda and KYOCERA
CO from 2012 for pulsed dipole kicker at first [4]. Figure 1 shows schematic view of the initial type CCiPM-D60,
whose bore diameter is 60 mm. And the copper conductor is
implanted in the ceramics. Some features are listed below.
• Air-core pulsed magnet• Apply comb coating to reduce eddy current effect• Low impedance• Compact and Light with structural strength• Flexibility of magnetic field

PULSED MULTIPOLE INJECTION
The pulsed multipole injection scheme has been developed and tested in KEK. In this case, the injection beam
is injected into storage ring by one pulsed multipole magnet. And the pulsed multipole magnet provides a nearlyzero magnetic field at center where the stored beam passes
by. Therefore, the stored beam will not be oscillated, whichmeans top-up injection will be transparent to users. Besides,
the pulsed multipole injection scheme only needs one magnet. Compared with bump injection scheme, it is a great
advantage from the point of view of space and magnetic
linearity of four bump magnets
In 2008, a pulsed sextupole magnet(PSM) was installed atKEK-PF and the beam was injected successfully [1]. However, the beam oscillation still existed. In later research, it’sfound that magnetic field generated by eddy current induced
the beam oscillation. In spite of the fact that the thicknessof one lamination steel is 0.15mm, it can’t suppress eddy
current completely due to a 1.2 µs short pulse width of current [2]. And coating will also generates eddy current field
acting on stored beam [3]. Despite the coating issue can besolved by optimizing the shape of coating, the eddy current
effects of iron-core is still remained.
Although, the beam oscillation was much reduced at
KEK-PF by pulsed multipole injection. It can’t meet therequirements about light axis stability in next generation
light source, which has much lower emittance and smaller∗ yaolu@post.kek.jp

Figure 1: Schematic view of CCiPM-D60.
Based on the theory of air- core magnet which is mainly
used in superconducting magnet [5], the CCiPM can generate octupole type magnetic field by placing the conductor
properly and applying the parallel current flow. As shownin Fig. 2, an octupole type magnetic field can be generatedby four parallel current flows in Poisson.
Thus, it’s possible for performing multipole injection
scheme by CCiPM.

Design and optimization
Although, in the next generation light source, the diameterof duct is usually about 30 mm, and a narrow bore type
CCiPM has been developed with a 30 mm diameter [6].
Though the CCiPM technology has achieved the productionof super narrow bore, to examine the injection performanceof CCiPM, a prototype CCiPM-D40 has been developed to- 39 -Proceedings of the 18th Annual Meeting of Particle Accelerator Society of Japan
August 9 - 11, 2021, Takasaki, JapanPASJ2021 MOOB03

Figure 2: Octupole magnetic field by Poisson simulation.
fit the duct of PF ring. The diameter of CCiPM-D40’s duct
is 40 mm. And to optimize the octupole magnetic field, theangle between the conductor and the mid-plane is designed
to be 45°.
The design target is that performance of magnetic strength
at kick point is similar with that of PSM to replace the PSM
in the ring, which means that integrated magnetic field is0.12 mT·m for an off-axis position of x=15 mm. And theapplied current is also around 3000 A.
Figure 3 shows the setup of CCiPM. At first, the terminalbox was applied to change the direction of current flow. But
it’s found that the inductance of circuit is 11μH measured
by LCR meter.

To solve these issues, a new model was proposed byadding four additional conductors on the surface of ceramics.
The simulation result by Poisson has been shown in Fig. 4.
The current flow direction of additional conductor is opposite to the current flow direction of inner four conductors.
The stored energy is reduced due to confining the magneticflux. And the model can be also simplified. Cable and terminal box are not necessary any more for the new model,
because the pulsed power supply system can be connectedto the CCiPM directly just by using two feed lines.
Besides, magnetic field around kick region to injection
beam is also increased. Figure 5 shows the comparison ofhorizontal distribution when current is 3000 A. The magnetic
field at kick point of new model is 0.04 T, which is larger
than that of old model(0.033T).

Figure 4: New model by adding additional conductors.

Figure 3: Setup of CCiPM.
In one-turn kick condition, the injection beam will only bekicked at the first turn. Because the revolution period of PF
ring is 0.624 μs, the pulse width of power source is designed
to be 1.2 μs. And the impedance will be about 30 Ω. The
peak voltage will be 90 kV if necessary current is 3000 A,
which indicates that the design is non-realistic. There aremainly two reasons why inductance of octupole type model
is high. One is that magnetic flux is full of space so that theelectromagnetic stored energy is large, which is shown inFig. 2. The other one is the twisted cable which can reduce
impedance of cable in dipole case, because the current flow
directions are opposite. But in the case of octupole type
CCiPM, it doesn’t work because of parallel current flows sothat impedance of cable can’t be ignored.

Figure 5: Comparison of horizontal distribution in different
models .
And the magnetic field of the new model is also simulatedby OPERA-3D, which can help optimize the structure ofbusbar to reduce the deformation of magnetic field along
longitudinal center axis.
Figure 6 is the conductor model in OPERA-3D. The lengthof each conductor is 290 mm. And the gap of busbar isnarrowed to reduce the deformation. The integrated fieldof 𝐵𝑦 along longitudinal center axis is only 9 μT·m. And
the integrated field of 𝐵𝑦 at x = 15 mm is 11.1 mT·m when- 40 -Proceedings of the 18th Annual Meeting of Particle Accelerator Society of Japan
August 9 - 11, 2021, Takasaki, JapanPASJ2021 MOOB03

electric discharge. From the simulation, the magnetic fieldalong center axis isn’t distorted by eddy current effect ofcoating. And the reduction ratio of magnetic field at kickpoint is less than 1%.

Figure 6: Conductor model in OPERA-3D.
current is 3000 A. It’s less than the target value but still
acceptable.
To fix the additional conductor, particular support wasapplied. Special jig holds the conductors precisely to keepthem in correct position by using keyway. Figure 7 shows
the design of 3D model. And the material of support is nonmagnetic to avoid undesirable magnetic field when pulsed
current is applied.

Figure 8: CCiPM model with coating in ELF/MAGIC.

PRELIMINARY TESTTo examine the performance of CCiPM, some offline experiments were performed.

Durability test
First, the baking and vacuum extraction were carried out
to check the heat durability and vacuum tightness. To meetthe requirement of installation at storage ring, the vacuum
should reach less than 1 × 10−7 Pa. During this experiment,
the temperature and the vacuum were detected by sometemperature sensors and an ionization gauge.

Figure 7: 3D model of CCiPM with four additional conductors.

Coating
As for the coating of CCiPM, uniform coating is appliedin design instead of comb coating adopted in dipole-type
CCiPM and the material is Titanium. The thickness of coating is 5∼8 μm. Based on previous measurement result, theuniform coating inside of a circular chamber hardly influences the magnetic field on the longitudinal center axis.
Besides, the reduction of magnetic field strength aroundkick region is negligible [2]. And transient magnetic field
simulation was also conducted to evaluate the eddy current
effects by ELF/MAGIC [7]. As shown in Fig. 8, the CCiPM
model with coating is constructed in ELF/MAGIC. The gap
between the conductor and the coating is 5.2 mm to avoid

Figure 9: Record of heating cycle baking.
Figure 9 shows a typical record of baking condition for
one period. Curves of temperature and vacuum undulates
regularly because a heating cycle is used as accelerated aging
test to simulate a severe situation for CCiPM assuming that- 41 -

Proceedings of the 18th Annual Meeting of Particle Accelerator Society of Japan
August 9 - 11, 2021, Takasaki, Japan

PASJ2021 MOOB03

the CCiPM will be used in the accelerator ring. One heating
cycle starts at room temperature, ramps to around 120 ℃and holds for 4 h, and cools down naturally for the other 4 h.
The baking was controlled by an automatic timing device
and continued for 38 days totally.
Finally, the vacuum could reach 7.6 × 10−8 Pa and leakage
didn’t happen, which shows good heat durability, vacuum
tightness, and its cleanliness.

Current Excitation test

Magnetic field measurement
Both DC and pulsed magnetic field were measured by a
3D mapping device. In the DC magnetic field measurement,
magnetic field measured by a hall probe and the current isset as 15 A. As for the pulsed magnetic field measurement, a
special probe has been made to measure the pulsed magnetic
field with external noise-less condition, which is different
from conventional method such as short coil or long coil [2].
The photo of pulsed magnetic field measurement is shownin Fig. 12.

Figure 10: photo of CCiPM on test bench.

Figure 12: Photo of pulsed magnetic field measurement.

As shown in Fig. 10, the CCiPM was constructed on test
bench. And the inductance is 1.45 μH measured by LCR
meter, which is dramatically reduced compared with previous original model. To examine the high voltage endurance,a current excitation test was performed by applying a pulsed
voltage to the CCiPM. The result is shown in Fig. 11.

And from comparison of horizontal measurement results
at center, which is shown in Fig. 13, it can be seen that DC
magnetic field result is almost same with simulation, butthere is a reduction in pulsed magnetic field measurement. Itwas though that the reduction of pulsed magnetic field wascaused by the SUS stage plate, copper conductor itself and soon. These candidates as the eddy current source are removed
by simulation test. More details should be investigated inthe future.

Figure 11: Result of current excitation test.
The peak pulsed current in experiment of new model isclose to 3000 A with a repetition rate of 10 Hz, but there
is a limitation of power source output. It also shows good
linearity and the pulse width of power source is 2.6 μs. And
there is no electric discharge in the experiment. And fromthe comparison with result of old model, the impedanceof new model becomes much smaller so that the current
increased much compared with that in experiment of oldmodel.

Figure 13: Comparison of horizontal distribution at center.

CONCLUSION
To solve the stored beam perturbation problem in pulsed
multipole injection, air-core pulsed magnet must replace the- 42 -Proceedings of the 18th Annual Meeting of Particle Accelerator Society of Japan
August 9 - 11, 2021, Takasaki, JapanPASJ2021 MOOB03

iron-core pulsed magnet. The CCiPM, which is developed
for a dipole kicker, is being developed and expanded toan octupole type pulsed magnet. A prototype of CCiPM
with 40mm diameter has been made to fit the duct of PF.
And additional conductors are designed to be on the surfaceof ceramics chamber to reduce the inductance. From thesimulation, the kick effect of CCiPM is almost same withthat of PSM at kick point. And some preliminary tests has
been conducted to examine performance. The mechanicalperformance is good enough and high voltage endurance isreliable. But in the magnetic field measurement, it’s foundthat normalized pulsed magnetic field is smaller than DC
result, which is against expectation. Further investigation isneeded to understand unknown issues.

ACKNOWLEDGEMENTS
One of the authors (Y. LU) thanks the help of T. Ushiku
from NCS company, the collaboration from KYOCERA Co,
and gratefully acknowledges the financial support from theChina Scholarship Council. This work was supported by
JSPS KAKENHI Grant number 19K2649(Representive, C.
Mitsuda).

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