Proceedings of the 10th Annual Meeting of Particle Accelerator Society of Japan (August 3-5, 2013, Nagoya, Japan)

FERRITE PROPERTY EFFECTS ON A FAST KICKER MAGNET
K. Fan#, K. Ishii, S. Fukuoka, T. Sugimoto, H. MatsumotoHigh energy accelerator research organization (KEK)

INTRODUCTION

to be use to speed up the rise time to 350 ns. However, themiss-matching circuit, together with other parameters,
lead to nearly 5% reflection tail field (Fig. 1). The longrise time of kicker field restricts the maximum beam
length in the ring, which prevents the implementation ofsecond harmonic cavities that is very important to reduce
the space charge effects in high power operation. The
remaining tail field will give excessive kick angle to thecirculating beam and causing beam losses.
To improve the kicker performance, methods of using
compensation kickers are being studied in parallel withthe main kicker upgrade [2]. Since the compensation
pulse is in the order of 100 ns, the magnetization rate isvery high, and the magnetization behaviour is entirely
different from DC conditions. Therefore, the magnetic
materials effects on performance is of a great concern,and the dynamic studies of magnetic materials have beentaken to know how the ferrite affects the kicker
performance. The main magnetic parameters of ferrite arefrequency dependent, which are characterized by thefrequency dependant complex permeability of ferrite,

The J-PARC is a high intensity proton beam accelerator
facility that consists of a LINAC, a Rapid Cycle
Synchrotron and a Main Ring (MR). The harmonic
number of the MR is nine. Four successive batches fromthe RCS are injected into the MR to fill 8 RF buckets
spaced at 300 ns interval. Fig. 1 shows the injection
scheme.

Where, s' is the real permeability, and s'' is theimaginary permeability. Fig. 2 compares the complex
permeability dispersion of three different ferrite materials
CMD5005, CMD10 and C2050 (Ceramic Magnetics,Inc.). The effects of the 3 different ferrite materials arestudied for optimization.

Abstract
The present J-PARC main ring (MR) injection system
employs four lumped kicker magnets. Their task is toinjection two bunches per cycle from the Rapid Cycling
Synchrotron to the defined bucket in the MR. The
operation must be loss-free to avoid any damage to theaccelerator. However, the present injection kicker’s field
have relatively long rise time and large reflection fieldthat do not satisfy the requirements of high beam power
operation. Besides the upgrade of the main kickers, twosmall fast compensation kickers are being studied inparallel to correct the main kicker performance. Sincehigh magnetization rates in magnetic materials areassociated with considerable magnetic losses, high quality
Nickel Zinc ferrite magnetic materials are required toensure the performance of the compensation kickers.
Therefore, the studies of ferrite materials effects on theparameters of both compensation kickers have carried out
to optimize the design.

 s   s '  j s ''Kicker field

1.0

Slow rise

0.6

Circulating beam
3rd Inj.

Injection beam
4th Inj.

0.4

Circulating beam
1st Inj.

Initial permeability

Normalized amplitude

1000
0.8

Circulating beam
2nd Inj.

0.2

100

C2050:
CMD10:
CMD5005:

100.0

Tail field

-1200

-600

0600

1200
1800
Time, ns2400

3000

3600

2

Tel: +81-29-8645272

3456 7 8 912345

6 7 8 9Frequency, MHz

102

3456 7 8 9100Figure 2: Basic parameters of ferrite.

The injection system must minimize the injection beamloss and place the newly injected beam onto the correct
trajectory, which is extremely important in high beam
power operation. To this end the critical demands are
posed on the kicker field, which must rise from zero to
full in the time interval between the circulating beam andthe start of the injected beam, and fall to zero within thetime interval and keep zero in order not interfering thesubsequent circulating beam.
The present injection kicker is lumped inductance type
and the field rise time depends on the total inductance inthe pulsed circuit. The total inductance of the present
kicker is nearly 1100 nH, and a miss-matching circuit has____________________________________________

u''s
u''s
u''s

4200

Figure 1: Injection scheme of MR.

#kj.fan@kek.jp

u's;
u's;
u's;

RISE COMPENSATION KICKER
Rise time improvement
The kicker excitation current shown in Fig. 1 starts atzero and exponentially grows to maximum in 350 ns. Theincreasing current is governed by,I  I 0 (1  e t )Where, I0 is the maximum current, and  is the time
constant determined by the parameter of R, L and C in thecircuit. The can be obtained by fitting the current thewaveform. The slow exponential growth current can bespeeded up by superimposing a small compensation
current as illustrated in Fig. 3. Practically, a small- 845 -Proceedings of the 10th Annual Meeting of Particle Accelerator Society of Japan (August 3-5, 2013, Nagoya, Japan)

correction kicker can be installed near the main kickers torealize this purpose.
1.0

Before compensation
Compensation
After compensation

Normalized Kicker field

0.8

0.6

140ns
0.4

350ns
0.2

0.0
600

800

1000

1200

1400

1600

1800

2000

Time, ns

Ferrite effects on coupling impedance
The beam passing through kicker aperture can becomea high power current source, which will induce magnetic
field inside the ferrite core that not only affects the beam
motion but also consumes considerable EM energy
causing temperature increase in the ferrite core. The effectis defined by the longitudinal coupling impedance, which
is dependent on the property of magnetic materials. Fig. 6
compares the longitudinal impedance with 3 different
ferrite materials.

Figure 3: Compensation kicker to fasten rise time.

Longitudinal impedance (Re),

400

Basic circuit
The basic circuit of the rise compensation kicker can berealized by a simple LRC series circuit as shown in Fig. 4.
The kicker excitation current is the capacitor discharge
current. In order to compensate the rise edge only without
introducing ripple to the flattop, a slightly over-damped
compensation current is needed, which is given by,i (t )  A1e

 0 (   2 1 ) tWhere,  0  1 / A2 e

RC / L is the damping factor.
2-6C2050
CMD10CMD5005

Coil inductance, H

2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
0

10

20

30

40

50

60

70

80

90

100

-400

102030

40

50

60

70

80

90

100

110

Figure 6: Longitudinal impedance comparison.

TAIL COMPENSATION KICKER
The irregular tail field (Fig. 1) provides different error
kick angle to different subsequent circulating beams. Thus,to correct these errors exactly a fast transmission line
kicker that can provide arbitrary waveform has beenstudied. Conventional transmission line kicker designuses parallel plates as cell decoupling capacitors, whichmakes the design and construction more complicated. Inorder to ensure the kicker field without any degradation
when travelling through the kicker, high cut-off frequencyof the kicker is a key parameters that is given by [2],fc Ferrite effects on circuit parameter L

3.0x10

C2050
CMD10CMD5005-200

Frequency, MHz

Figure 4: Basic circuit of rise compensation kicker.
The compensation current pulse shape is required to bevery delicate to correct the rise time exactly. However, theinductance of the compensation kicker is determined by
the ferrite material which is frequency dependent. Thus,
the material property may have considerable effects on
the performance of the compensation kicker particularly
at high frequency range. In view of magnetic field
generation high permeability materials are preferable. Buthigh permeability materials normally have narrow
bandwidth, which will degrade the signal response at highfrequency. Fig. 5 compares the frequency dependent coilinductance using different ferrite materials.

00 0 (   2 1 ) t

LC is the radian frequency, and2001
 ( Ln  4 Lcs )Cn(2)Where, Lcs the stray inductance of cell capacitor. Fig. 7
shows the basic circuit of the tail compensation kicker
system.

Figure 7: Tail compensation kicker circuit.

Transmission line kicker with lumped capacitor
Conventional design of transmission line kicker has
high frequency property because of the interleaved highvoltage plates as cell capacitance can provide very small
stray inductance [3]. However, it is difficult to reduce thecharacter impedance of the kicker due to the vacuum
dielectric materials, which limits the excitation current.
To further reduce the impedance, lumped capacitor withhigh permittivity dielectric materials is implemented. The
structure is shown in Fig. 8.

Frequency, MHz

Figure 5: Coil inductance vs. frequency.

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Proceedings of the 10th Annual Meeting of Particle Accelerator Society of Japan (August 3-5, 2013, Nagoya, Japan)

longitudinal coupling impedance, which is because of thecell capacitors. Fig. 11 compares the coupling impedance
calculated in three different ferrite materials.

Figure 8: Tail compensation kicker.

1000-300

1614121086420-2-4-400

05101520253035404550Frequency, MHz

102030405060708090100110Frequency, MHzCMD5005
CMD10C2050

Figure 11: Longitudinal coupling impedance comparison.
The coil inductance and the kicker impedance made offerrite C2050 has considerable oscillations even if at lowfrequency, which makes the performance unstable.

Ferrite effects on magnet impedance
In ideal case the characteristic impedance is constantwithin the working frequency. However, the frequencydependent property of magnetic materials and thecomplicated structure enlarge the parasitic effects, which
has considerable impact on the compensation kickerperformance. For instance, the transmitted parameter Z21
is seriously deformed as shown in Fig. 12, which will
deform the kicker filed shape.
CMD10, capacitor: 500pF
CMD10, capacitor: 500pF

28060240
40

Transmitted Z21

Cell inductance, nHC2050
CMD10
CMD5005

18-2000The character impedance of each cell of thetransmission line kicker must be uniformly distributed toeliminate the reflection field and to suppress field ripple.
The cell character impedance is defined by the cellinductance and the cell lumped capacitance. However, thecell inductance is determined by the ferrite property andthe location of the individual ferrite blocks. The
compensation kicker consists of 20 ferrite blocks withthickness of 20.5 mm separated by 2 mm copper plates asshown in Fig. 8. The cell inductance can be determined by
the magnetic flux of each ferrite block, which is shown inFig. 9.

8020-100Ferrite effects on circuit parameters

100

C2050
CMD10CMD5005

200

Longitudinal impedance (Re), Longitudinal impedance (Re), 300

20Ferrite blocks
01243219 20

468101214161820

Number of ferrite

Figure 9: Cell inductance distribution (DC).

CMD5005
CMD10C2050

0-20-62.0x101.8

Coil inductance, H

Coil inductance, H

20-40-60-80x10

1.4

0.1

2345 6 7 8 912345 6 7 8 9Frequency, MHz

102345 6 7 8 9100

Figure 12: Frequency dependent Z21.

CLUSION
Compensation kickers together with upgrade of themain kickers will improve the performance greatly, andcan satisfy the requirements of high beam power
operation. A simple prototype transmission line kicker
has been developed [3] for proof of principle andparameters test.

REFERENCES

1.00.80.6
0.4
0.20.138000.1

1.2

0.02120

CMD5005
CMD10C2050

1.6-6160

40

It shows clearly that the cell inductance is location
dependent due to the different leakage magnetic flux. The
cell inductance is frequency dependent also. Fig. 10compares the total coil inductance versus three different
ferrite materials. The AC inductance is larger than that
calculated in DC case.
40200423456 7 8 9123456 7 8 910Frequency, MHz5 6 7 812345 6 7 8102345 6 7 8100

Frequency, MHzFigure 10: Frequency dependent coil inductance.

Ferrite effects on coupling impedanceComparing to the lumped inductance rise compensation
kicker, the transmission line kicker has relatively small[1] K. Fan et al, “Upgrade design of injection kickers for
JPARC main ring”, PASJ’2009.
[2] L. Ducimetière, “Advances of transmission line kicker
magnets”, PAC’2005.
[3] S. Fukuoka, K. fan et al, “Development of a fastcompensation kicker system for J-PARC maing ring
injection”, IPAC’2013.

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