JAERI-Conf 95-021

PB13
Recent Improvement of Ripple Performancein HIMAC Synchrotron Power Supply
M. Kumada,K.Noda, E.Takada, M.Kanaza,va, N.Araki, S. Sato, A. Itano 1,H.Kubo 2, T. AokP,S. Matsumoto\ K.Sato 5·National Institute of Radiological Sciences
4-9-1 Anagawa, Inage, Chiba, japan(e-mail) kumada@nirs.go.jp,

ABSTRACT
Ripples in the HIMAC synchrotron power
supply and the admittance of the load weremeasured and confirmed to be small as 3 ppm
for the Quadrupole Power Supply right after
the commissioning. Further improvementwas focused on the 50 Hz and 100 Hz ripples
which were major component deteriorating
the spill. By re-tuning the power supply, wecould reduce the ripple to a level of 0.3 ppm' l.
The study of the relation of the ripple andthe beam spill revealed that the fluctuationof the beam spill is affected by the ripple in
Bending magnet power supply in addition tothat of the Quadrupole. After finding thisfact, the beam spill became more uniform inroutine operation by re-adjusting theSextupoleandQuadrupolestrength.
Encouraged by this performance, theBending magnet power supply is upgradedby adding the active filter and the new DCCT.
With this improvement the ripple became ata level of 0.2 ppm and the beam spill wasimproved.
I. INTRODUCTION

In a synchrotron the current of themagnet string has a trapezoidal form.
Because of the resonant beam extraction, theripple content should be a few ppm or less at
the flat top. The basic ripple frequency fb=1200 Hz of the power supply is given by thefrequency of the power source(f0 =50Hz)
multiplied by the number of thyristors(24).
The Fourier analysis of the ripple voltage

also gives multiples of fb. Another ripple
with the frequency of 2nf! is caused byimperfections of the transformers and byvariations in the triggering of the thyristors.
Furthermore oscillatory spike voltages are
induced across each thyristor. The spikes are
modulated by low frequencies and can also
contribute ripple at frequencies as low as
100 Hz. Other problem associated with themis the production of noise spikes inequipment located in the neighborhood. In
spite of various efforts, the reduction ofspikes and ripples has been unsatisfactory
for the requirement of the tolerance of thethird order resonant extraction. To fulfill therequirement for beam extraction, in mostof the accelerator in operation, additionalmean such as spill feedback controller must
be applied.
In the HIMAC synchrotron power supply,
a new approach is taken.
II. HIMAC approach
We started from the proposition that theload of the synchrotron power supply is acascaded string of the magnet inductance, its
resistance and the capacitance between theexcitation coil and the iron yoke. Typicalmagnitude of the capacitance of a
Quadrupole magnet of a standard size isestimated to be a few nF. The iron yokes areassumed at a ground potential. At the Hll\IIAC
the yokes are connected by the earth line.
The schematic diagram is depicted in Fig.l.
This model circuit is a six terminal circuitthat has parallel and series resonance. Due toHyogo Prefectural Governernment
Hitachi Ltd.
3 AEC, Accelerator Engineering Corporation' Dokkyo University, School of !'vledicine
5 RCNP, Osaka University
12-284-

JAERI-Conf 95-021

The ripple component of SO Hz and 100 Hz
were the main component seen in the outputof the power supply. The fluctuating
component of the beam spill appeared to be
100 Hz. 100 Hz is caused by the imbalance ofthe phases of the AC power line. But SO Hz can
not be generated by the imbalance. Thesefrequencies can not be damped by the low
pass filter as the cut off frequency of bothmode is chosen to be 7S Hz. Lowering the cut
off frequency helps in reducing the ripple
but slowing the response of the trapezoid
pattern and deteriorating the tracking
accuracy between the Quadrupole and theBending magnet. We decided to strengthen
the active filter of the Quadrupole by adding
the bandpass filter of SO Hz and 100Hz for theindividual fine tuning of the phase control.
The bandpass filter worked fine as expected
and the ripple was reduced. Through thecareful study of the SO Hz source, we fouridthat the SO Hz is originated from the DCCT.
Although the relative amplitude of the DCCT
was small as SO ppm, it has been aperformance limiting factor to go below ppm
level. With bandpass filter the relative ripple
content became at a level of 0.3 ppm for thetime. The main frequency of the beam spillchanged from 100Hz to SO Hz. We found thatthe 100Hz was a superpositio n of the SO Hz
ripple of two different sources whose phases
are shifted, namely from the power supply of
the Focusing Quadrupole and that of theBending magnet. The remained SO Hz
originated from Bending magnet power
supply. The change of tune of the beam is
speculated to come indirectly throughSextupole magnet that compensate thechromaticity . This was verified that by
reducing the Sextupole strength, the better
quality of the beam spill is obtained. With theevidence that the present beam spill isaffected by Bending magnet, we decided toreduce the ripple current in the Bending
magnet by adding the active filter of thesimilar type of the Quadrupole power supply.
The inductance of the Bending magnet load issix times larger than that of the Quadrupoleand supplying larger power is required.
Typical reduction of 2S dB at 100 Hz wasachieved after an elaborate adjustment of thecut off frequency of the high pass filter thatis incorporated in the active f'Jlter circuit.
Typical example of the frequency spectrum at600 MeV/u with and without active filter areshown in Fig.2. where SO Hz is reduced by 28
dB and 100 Hz is 32 dB. The small SO Hz ripple
is also due to the installation of the Holec DCCT.
Its linearity and the stability are checked andimplemented into the ACR feedback circuit.
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Fig.2 Ripple voltage spectrum of theBending magnet at 600 MeV/u without(upper graph) and with (lower graph)active filter.
IV. ACKNOWLEDGMENTS
We gratefully acknowledge the support ofthe members of the division of accelerator
physics and engineering and AEC. The
author thanks the enlightenin g discussion
with Prof.Y.Irie of KEK.
V. REFERENCES[1] M. Kumada, to be published in NIM.
[2] M. Kumada , to be published in particle
accelerator .

-285-JAERI-Conf 95-021(2)where Yno and Yeo is the characteristic
admittance of the ladder circuit. to and ~and the are expressed by(3)~· Nlower

No. (N-I)lowt.,.._JN
Fig. 1 An equivalent circuit of the HIMAC
magnet string.

a presence of the capacitance to the ground,the incoming current I to the load and theoutgoing current J from the load are not
identical as contrast to the ordinary model of
without the capacitance to the ground. The
difference current I-J flows back to theneutral point of the thyristor bank. The
potential at the neutral point develops and is
known as a common mode voltage. In thecase of the grounded neutral as in the HIMAC
this potential is small. In order to estimate
the magnitude of the ripple current we needto know the resonance frequencies and theadmittance. If the spike frequency or theripple frequency overlap the resonance ofthe magnet string, the ripple current isenhanced. To avoid the overlap, theknowledge on frequency characteristic of
the load is required. No previous analysis
was done in the past. Computer simulation istime consuming. By applying eigenvalue
technique, we found that six terminal circuit
can be reduced to two set of orthogonal four
terminal circuit. We found as a special casedecomposition into the normal mode and thecommon mode is possible. The normal mode
voltage and current is defined as U+V and I+J
and the common mode voltage and current isdefined as U-V and 1-J respectively. With themode separation, the normal and thecommon mode admittance Ync of the magnet
string, which we model as a ladder circuit,can be written down simply as,

Zn.c is the mode impedance of the magnet
and Ync is the mode admittance expressed by
the capacitance to the ground. Above
equations are simple yet ,very powerful tofully describe the magnet string of resonant
feature 2l. The analytic solution in time
domain is possible by Inverse Laplacetransformation 21 • The admittance of theHIMAC magnet string was measured and thevalidity of the present model was verified.
The current ripple is estimated using theadmittance from the voltage ripple of thepower supply. At the HIMAC the resonancecan be suppressed by the bridge resistor
parallel to the magnet. This resistor also
helps to bypass the ripple and spike currentof the magnet.
With a finding of the presence of two
orthogonal mode in the load, the model of themode separation is extended to the power
supply side. Direct consequence of thepreceding argument is the addition of thecommon mode low pass filter. Without thisfilter, the common mode ripple voltage isdirectly applied to the magnet string.
Furthermore the common mode current in
the HIMAC Bending magnet string is
considerably reduced as the magnetic field
because of the separate connections of theupper and the lower coils due to the natureof the parallel direction of the current.
In this way, in the HIMAC, most of theripple voltage of the normal and common
mode is suppressed. The relative ripple
current of the Quadrupole with active f"tlter
was 3 ppm and that of the Bending magnet
without active filter was around 5 ppm rightafter the initial operation. It appeared thatthe beam spill did not reflect the small ripple
content the study was continued.

(1)III. Improvement at the S_OHz and 100Hz
ripples-286-