The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

IMPROVEMENT OF FIELD SIMILARITY OF PULSE BUMP MAGNETS
T. Ohshima*, SPring-8, Hyogo, JapanAbstractTop-up operation is planned at SPring-8 from thisautumn. It is important to reduce the oscillation
amplitude of stored beam during beam injection.
Deviation form similarity in magnetic field of pulse
bump magnets is one of the perturbation sources. The oldbump magnets were composed of stacking the thinelectromagnetic steels, which were supported by metallic
end plates. The eddy currents induced at the end plates
mainly contributed to this deviation. So, we replaced thepulse magnets to new ones, which have non-metallic end
plates to suppress the effect of eddy current. The field
patterns measured by using a search coil were improved
and the reduction of beam oscillation was observed bybeam test.

inductors were carefully selected. The transmission
cables from power supplies to magnets were replaced tosame type of coaxial ones with same length in summer of2001. But there still remained some differences inwaveforms. In this paper we present how we measure
the field and how we improve the similarity of magnetic
fields.
Table 1: Parameters on bump magnets
MagnetBP1

L@1kHz5.6µH

Dimension ofpole (mm2)
320*110

BP2BP3BP4

4.8µH
4.8µH
5.6µH

170*130
170*130320*110βx(m)4.1

kick(mrad)
-2.33

22.9
22.9
3.7

-0.65
-0.55
-2.35

INTRODUCTION

MEASUREMENT OF MAGNETIC FIELD

The SPring-8 is a synchrotron radiation source of thirdgeneration. It consists of 1 GeV linac, 8 GeV booster
synchrotron and 8 GeV storage ring. Top-up operation
will be introduced at SPring-8 in this autumn. This
operation mode reduces the change of heat load of opticalelements such as mirrors of monochrometers. The top-up
operation mode also enables to use high current bunches
which have short beam lifetime. To make top-up mode inuse for experiments there are many hurdles to overcome.
The reduction of oscillation of stored beam caused by theinjection bump orbit is one of them. The sources of theoscillation are (1) imperfection of similarity of four bumpmagnets and (2) non-linear effects from sextupole
magnets located in the bump orbit. The detail on thelatter topic will be reported in another letter [1] and here
we concentrate on the former topic.
We use four pulse magnets to produce the injection
bump orbit. The pole of the magnet consists of a stack of
0.1mm thick electromagnetic steels. The turn number ofthe coil is two. The gap is 56mm. There are two types ofmagnets; long pole type one (BP1 and BP4) and shortpole type one (BP2 and BP3). Table 1 shows the main
parameters of them. The designed waveform of magnetic
field of the bump magnet is half sine whose width isabout 8µs. Actual waveforms of magnets have slightdifferences from each other but they satisfied thespecification designed at construction stage of theSPring-8. These small differences however shake thestored beam and cause problem at top-up operation. To
reduce the differences the current waveform were firstlyadjusted. The values of charging capacitors and matching

We measured the magnetic field distribution using asmall search coil whose diameter is 10mm at the test
bench. The coil was mounted on movable x-y-z stages.
The output of the coil is also connected to a twisted cableand to the probe of the oscilloscope. The bandwidth of
the scope is 300MHz and the sampling ratio is 500Ms/s.
A personal computer is used to take data from theoscilloscope and to control the xyz-stages. The magnetic
field is obtained by numerically integrating the output
voltage of the search coil.
To measure the integrated magnetic field along z-axis(beam axis), two long coils are used. The widths of thecoils are 1.27mm. The lengths of the coils are 350mm forthe long pole magnet and 220mm for the short polemagnet. This coil is also used to measure the magnetic
field of each bump magnet at the actual position in thestorage ring. The output of the coil is connected totwisted cable and to the probe of the oscilloscope.

_____________________*ohshima@spring8.or.jp

RESULT OF FIELD MEASUREMENT
Figure 1 shows an example of field pattern in time
domain taken for the BP1 magnet. A line with filled
circles shows the output voltage of search coil and a linewith triangles shows the integral of the output voltage.
Typical rms errors in measurement are about 2% in thepeak amplitude and about 7ns in timing at peak value ofthe magnetic field B. The measured field distributions
along z-axis (beam axis) and x-axis (perpendicular to zaxis in a horizontal plane) are shown in figure 2 for theBP1 magnet. We could find the field is decreased toabout 1/10 of maximum value at a distance of the gap
length.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

voltage

0.20B (arb. unit.)

0.10BP1BP2BP3BP40.8

B (T)voltage (V)

1B

50

0.6
0.4
0.2

A

B

0-0.1
-0.2-2-505time (µs)

1002-0.2
15

Figure 1. Example of output signal from the search coiland its integral.
Figure 3 shows the time evolutions of the magnetic
field for four bump magnets measured by using the longcoil. The peak values are normalized to one. We could
find field deviations near starting point (A in the figure)and end point (B) of the half sine wave. The deviation atthe point (A) may be caused by the difference inoperation parameters of the thyratron in the power supply.
The deviation at the point (B) may be caused by thedifference in effect of eddy current at somewhere themagnetic field is strong. Two 20mm thick SUS plates
were used to support the stacked electromagnetic steels.
The coils were wound including these end plates. It is
probable that the time varying magnetic field generates
eddy current on the SUS end plates, which change theshape of magnetic field at the point (B). The effect ofeddy current is stronger in the short pole magnet than thelong pole magnet because the ratio of the endplate-length
to the pole-length is larger in the former than the latter.

46time (µs)

81012

Figure 3. Time evolution of magnetic fields of old bumpmagnets: BP1, BP2, BP3 and BP4.

IMPROVEMENT OF FIELD SIMILARITY
We made new magnets to reduce the effect of eddy
current at the end plates. The material of end plates ischanged from SUS metal to glass-epoxy-mat, which isnon-conducting material. Figure 4 shows the measured
inductance for the old and new bump magnets. Newbump magnets show larger inductance at high frequency.
BP1BP1EX
BP2BP2EX

76L (µH)

-50

543

1

By along x-axis
By along z-axis

20.1

1

10100
frequency (kHz)1000

Figure 4. Inductance of old magnets (BP1, BP2) and newones (BP1EX, BP2EX).

0.01

In order to check the performance of new magnets at theactual setting, we replace the old bump magnets in thestorage ring to new ones and we measured the magnetic
field using the long coil. The shapes of field patterns
were improved and the deviations at the point B weredecreased from 7% to 2%. The remained smalldeviations may be caused by the difference ofenvironment such as different shape of ceramics
chambers, different geometry of electric shield made ofaluminium plates and so on. We insert a field cramp

B (T)

0.1

0.001
-100

-50

050x or z (mm)100150Figure 2. Distribution of the peak field of BP1 along xaxis and z-axis.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

1bp1ex
bp2ex
bp3ex
bp4ex

B (arb. unit.)

0.8
0.6

1.5
1
0.5
00.4

00.2

5

1015time (µs)

2025Figure 6. Oscillation amplitude of stored beam before
and after replacement of bump magnets.

0-0.2-2

beforeafter2rms (mm)made of a stack of electromagnetic steels with 0.1mm
thick. The cramp absorbs the filed leaked from the pole
gap and reduce the effect of eddy current produced by thevacuum chamber next to the ceramics duct or thealuminium electric shield. The similarity of the field isimproved by the cramp and the result is shown in figure
5.

024
6time (µs)

81012

Figure 5. Time evolution of magnetic fields of new bumpmagnets: BP1EX, BP2EX, BP3EX and BP4EX.
The beam test was performed to verify the effect ofthese improvements. The oscillation amplitude of thestored beam was measured by using a turn by turnmonitor. Figure 6 shows the result. Horizontal axis
shows the time after beam injection with an offset of
4.5µs. Vertical axis shows the rms oscillation amplitudeof stored beam. A line with filled circles shows theoscillation amplitude with old bump magnets. A linewith triangles shows the amplitude with improved newbump magnets. The peaks at 2µs and 7µs are due to nonlinearity effect of sextupole magnets in the bump orbit.
Since the revolution time is 4.8µs, the shape of theoscillation after 10µs repeats in the duration of 4.8µs andthis amplitude is damped with the damping time of 8ms.
A large peak at 9µs before improvement is produced by
the field irregularity at the end of the waveform ((B) in
the figure 5) and this amplitude is reduced to 1/10 after
the improvement.

CONCLUSION
By using new bump magnets with non-metallic end
plates, we could reduce the effect of eddy current. This
results in improvement of the similarity of the field shapefor four bump magnets. The amplitude due to the fielddeviation at the end point of the waveform was reduced
to about 1/10. Further efforts will be made to improve thesimilarity of field shape such as model calculation formatching of the power supply and the magnet, precise
measurement of the effect on the magnetic field shapeform the aluminium shielding plates etc. We also observe
the vertical kick by the bump magnets at a beam test. We
are now preparing a remote controlled height adjuster
and we will adjust the tilt of the magnet to minimize thevertical kick. The effect from non-linearity of sextupole
magnets will be reduced by adjusting the strength ratio ofsextupole families. The detail of this method will beshown in another paper.

ACKNOWLEDGEMENT
The author thanks to H. Tanaka, S. Nagasawa and M.
Yosioka for their help during the width adjustment, K.
Kajimoto for his help in programming data acquisition
system. He thanks to S. Matsui, K. Soutome, M. Takaoand H. Ohkuma for their supports. He thanks to K.
Kumagai for helpful information. He thanks to H.
Kanazawa of Nishishiba Electric co. LTD. for his effort
during production of new bump magnets. He also thanks
to N. Kumagai who suggested initial idea to exchange
the end plate to non-metallic material.

REFERENCES[1] H. Tanaka et. al. , to be published.