The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

New magnetic material for proton synchrotr on RF cavity
Tomonori UESUGI~ Eizi EZURA 1 , Chihiro OHMORI, Kiyomi KOBA 1 , Kazuyoshi SAITOHt
Shinya SAWADA, Akira TAKAGI\ Tetsumi TANABE*, Yoshio TANABEf Makoto TODA 1 ,Hitoshi NAKAYAMA, Miho FUJIEDA~ Yoshiharu MORI, Taixuan YAN~Masanobu YAMAMOTO~! Masahito YOSHII 1KEK-Tanashi, 3-2-1 Midori-cho, Tanashi, Tokyo 188, JAPAN1 KEK, 1-1 Oho, Tsukuba, Ibamki305, JAPANAbstract

F1xed vocuum condenser

We have measured the characteristi cs of the high permeability magnetic materials, auch as ferrites, amorphousand FINEMET. The measuremen ts have showed thatthe FINEMET is the most excellent material for theRF cavity of high intensity proton synchrotron s.
Vorioble1

LU~ii~~~!ii;&vocuum

Introductio n

The RF cavity of proton synchrotron s requires high permeability magnetic materials for tuning the resonant frequency. We have been seeking the best materials for
the RF cavity of the JHF proton synchrotron s [1] so far.
Among the samples, we were interested in new magnetic material, 'FINEMET' , which is stable against thehigh RF magnetic field and high temperature[2][3]. TheFINEMET core is not a Fe-based soft magnetic alloy
composed of amorphous and ultra-fine grain.
We have measured several types of FINEMET coresin detail. In this paper, we report the results of thesemeasurements.
2Experimen tal Apparatus

In order to measure the impedance of magnetic material,
we fabricated a resonant test cavity with the variable capacitors. The impedance of the materials is obtained bymeasuring the waveform of the voltage and the current
in the cavity. The test cavity is shown in Fig 1. A magnetic core was put between two cooling plates of thecylindrical cavity. The RF power was introduced into
the cavity via RF feeder.
The input RF power was limitted to 1kW by thepower amplifier. Azimuthal bias magnetic field for frequency tuning was applied by a bias current generator
which supplies DC current up to 1000A.
The measuremen ts have been done for three ferrites, an amorphous and eight FINEMET cores. The*Also CNS, Univ. of Tokyot Also Hitachi Co. Ltd.
t Also Toshiba Co. Ltd.
§Also Institute for Chemical Research, Kyoto Univ.
'II on leave from The Bureau of Basic Sciences of AcademicChina
II Also Research Center for Nuclear Physics, Osaka Univ.

condenser

Figure 1: Cross section of the test bench.
no.
code name
O.D.
I. D.
th.
1
FT-3M
579.0 320.0 25.3
2
FT-lH
70.0
32.0 25.0
FT-1L
370.0
32.0 25.0
4
FT-3H
70.0
32.0 25.0
5
FT-3M
70.0
32.0 25.0
6
FT-3L
70.0
32.0 25.0
FT-3M(epoxy) 340.0 140.0 25.0
78FT-3M
340.0 140.0 25.0
Table 1: List of FINEMET samples. Each column shows
the material code name, outer diameter, inner diameterand thickness in the unit of mm.
FINEMET cores we measured were listed in Table 1.
Three of them has a practical size and the rests aresmall. The code name in the table shows the materialtype(numbe r) and the magnetic anisotropy(a lphabet).
The FT-1 series has an extremely lower magnetostric tion constant compared with that of FT -3 series whose
are about 2.3. The anisotropy index describes the direction in which the external magnetic field was appliedat heat process, i.e. axial(L), azimuthal(H ) or no direction(M). All of the cores except #7 has a Si02 coatingon the surface.
33.1

Results

The dependence on the RF field strength

The dependence of impedance on the RF flux density for
two FT-3M samples is shown in Fig 2. For comparison,
the characteristi cs of ferrite materials; Ni-Zn and Ni--188-

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Zn-Co are also shown. The P,pQ[ means the productof the permeability, quality factor and RF frequency.
It is a size independent parameter propotional to shunt
impedance, that is,::t300~~~~-~l;:ij_!r.~~_i~~r.ite_)_ __250 -- -------·---------------'J:. __!ol FT -3M(FIN~MET).

200----------------------------1--------------------------------------+-------------------------------

where:::: P,ot l (O.D)

150

The maximum RF flux in this measurement was limitedby the power amplifier. We found that p,Q f was constant even at the high· RF magnetic field strength up to2000 G. This is one of the most ·interesting characteris;:
tics of the FINEMET cores;

100a2rr n I.D ·50ldc(A).
Figure 3: Bias field dependence of FT-3M.

···················- - -------.-sYZ(fili=-zn··rerrlte}""·-------------·--o- 4M2(Ni~Zn=Cq ferrite)• FT -3M( small) !

-is the best for the JHF synchrotrons because; (1)it has
the highest shunt impedance, and (2)its quality factor(Q "' 1) is not too low compared with the other typesof FINEMET cores.

10 _ ---------------------- --- --------e::-FT::-,c:3f'o1{lo:rg:e}:::::j: ·-------------------·------·--··········-:-··············-··-···········

103.4Fig 5 compares the impedance of a Si0 2 insulated core
and an epoxy insulated core, which was measured witha LCR meter. We can found little difference in p,Q f andno difference in p,.

1L--....................J_~~......J.....,......~........J..........~..........J
110103
104

B,,(gauss)
Figure 2: Shunt impedance of FT-3M vs RF flux density.

3.2

comparison of insulation material

Bias field dependence

The bias field dependence was measure.d at a low RF
voltage, "'5V. It has been proved by the previous measurement that such a low RF voltage does not affect theimpedance. Fig 3 shows the bias field dependence of_permeability for theFT-3M large core at the frequencyof 3.0 and 4.0MHz. The relative permeability was calculated by the following eq.

3.5

Temperature dependence

Temperature dependence of an amorphous core 'metglas' and FT-3M was measured with a thermocouple
which is placed on the inner edge of the core. Temperature was raised up to 140 ·c when high RF was introduced. The shunt impedance of metglas rose 45%.
However, there were no variation in characteristics ofFT-3M. It is reasonable because the Curie temperatureof FINEMET, 570 ·c, is higher than that of metglas,
410·c.
4

Z = iWO:f.-tr·Fig 3 tells that the permeability of FINEMET can bevaried more easily than that of ferrite. However, thetuning is not necessary for the FINEMET cavity because
the FINEMET has a broad band impedance curve [5].

3.3 comparison of FINEMET types
We measured the impedance as a function of frequency
for all of the FINEMET cores we had. The RF voltage
we chose here was 5V. Figure 4 shows the results forthe five small samples. The 'H' type material has asmall shunt impedance (or p,.pQf product), thus it isnot useful for the RF cavity. We think that the FT-3L

Summary

We have measured .the characteristics of FINEMET
cores and compared with the ferrite materials. TheFINEMET cores showed the high shunt impedance ata few MHz frequency and both their :1' and Q value
were extremely stable- under the high RF magnetic fieldstrength and high temperature. And, the FINEMET
cavity can damp the coupled bunch instability[4], because of its low quality factor (Q"-'1). The cllaracter~tics of the FINEMET is similar to those of soft magnetic
materials as metglas. The metglas has temperature dependence, because of its relative low Curie temperature,however, the FINEMET does not have 'at the temperature of 150 ·c.

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The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997::t2oooo I
18000 !-\····················· +·····························c·························•··+-+T·-lH · ····I•

16000;

f···········

T-1 L+·································· ·· ················O··FT-3Ho T-3M·:~~~ ~~············· ··'·································:······················~>· FT-3L ·10000~~\\\\·········'···+·······························;··························· ·+···············::::<DOD~~
r~~·········. . . . ,'. . . .

··I+ .. .

20000o.......... ---..

::{20000

264818000.
: ~t5~t$f~,)y}16000 !-····················!······························································+·····················I

frequency(MHz)14000,..-._812000NIC)..___.,_•

70::t

T -1 H

10000-1L
T-3H"-

8000

T-3M···

6"T-3L

6000

54000 f- ........................ , .............. cc.""'"'*'=. .:. . .

42000 f- ...........................................................................

30 0';--'-~~-7-~~-'-:':~~~-!;--~~........42

frequency(MHz)8r---~-----~-----,

X

frequency(MHz)Figure 4: Comparison of FINEMET cores.
References[1] Y. Mori et al., The Japanese Hadron Facility, Proceedings of 1997 Particle Accelerator Conference,Vancouver, B.C., Canada 1997.

32[2] T. Uesugi et al., Summary of the measurement ofmagnetic materials for JHF RF cavity(1), JHP-31,
Internal Report of JHF( only in Japanese).
[3] M. Fujieda et al., Studies of Magnetic Cores for JHF
Synchrotrons, Proceedings of 1997 Particle Accelerator Conference, Vancouver, B.C., Canada 1997.
[4] T. Uesugi et al., Longitudinal Coupled Bunch Instability in the JHF 50GeV Main Ring, Proceedingsof 1997 Particle Accelerator Conference, Vancouver,B.C., Canada 1997.
[5] C. Ohmori et al., A Broad Band RF Cavity for JHF
Synchrotrons, Proceedings of 1997 Particle Accelerator Conference, Vancouver, B.C., Canada 1997.
[6] M. Fujieda et al., A Broad Band RF Cavity for JHF
Synchrotrons, these proceedings.

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frequency(MHz)Figure 5: Comparison of insulation material.