The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

R&D and System for KEKB Magnet Power Supply
Masato YOSHIDA, Tadashi KUBO, Atsuyoshi AKIYAMA, Tatsuro NAKAMURA, Shinichi YAMAMOTO *High Energy Accelerator Research Organization
1-1 Oho, Tsukuba, lbaraki 305, Japan*ATC Co., Hachioji, Tokyo 193, Japan

Abstract
There are several demands for magnet power suppliesof KEKB accelerator. First is high current stability for
year and low current ripple. Second is high efficiency andcompact. Third is high speed current control for correction
magnet power supplies. Fourth is reducing a cost ofwhole power supply system. After carrying out many
R&D, we have solved these problems.

External Form Size: Max. 200(W) * 150(0) * IOO(H) (mm)Fig. 1 Temperature compensator forB, Q and QCS.

1 Introduction
For magnet power supplies of KEKB, required current
stability is very severe. Especially, for bending (B),quadrupole (Q), and super conducting quadrupole (QCS)
magnet, current stability is 100 ppm(p-p )/ year andmagnetic field ripple content rate is 10 ppm(p-p) (>0.2Hz)(1). Even more, currents of correction (St) magnets must
be controlled quickly and synchronized the other magnets'
currents (2). Much more power supplies (about 2,500)
than TRISTAN accelerator must be installed in theexistent power supply rooms. These rooms are very small
for installation of all power supplies for KEKB and haveno air conditioner except for cooling fans. Because of lessconstruction cost in comparison with one of theTRISTAN, we must make power supply to be small andbe high efficiency to reduce the cost. Then we decided tointroduce new interface system instead of CAMAC toreduce the cost and to satisfy the requirements of the highspeed operation for the St magnet.
After many R&D to satisfy requirement for current
stability through the year, we decided to introduce verysmall temperature compensator which contains importantparts to realize the high stability. As a result, we haveintroduced switching mode power supplies to makesmaller its size and to reduce the heating loss except forhigh voltage and large power power supplies. For theinterface, we introduced ARCNET (Attached Resource
Computer NETwork) system consists of serial bus (3).
In the next section, we will describe many R&D, andreport the whole power supply system including current
monitor and interlock system.

2 R&D of Power Supply
2.1 Temperature Compensator
Before introducing the small temperature compensator,
we were going to set the control units of power supplies
in air conditioned room (1). However it proved to be thecost is very high and the stability of the temperature is
not good. New temperature compensator is very small.
Fig. 1 shows a schematic drawing of the temperaturecompensator. This has a DAC, two burden resistors andail error amp. which are most important parts to realize
high current stability of power supply. Fig. 2 shows ablock diagram of the parts.

16 Bits Current Data
Interface Board....-::-_J__--;-_-,_ - - - - -,W.:~~=~

r-=*:-:c.,..-, ] Double Buffere tster

L _ -· _ _ _~~Current .
Monitor

B,Q&QCSPowersupply~~~~~~-----------.

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11:

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I~--~~------------~III
I Current Outpu~ _ _!)Q;T_ _ .

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IL _______ j
L~m_Eer~ui!_C£.._m~ns~o~====- j:____ _________ _Fig. 2 Block diagram of important parts.
Temperature Compensator Test
Several performances of temperature compensator madefor R&D have been measured. As a result, we decided touse the copper for cooling or heating plate because thechange of the resistance value of burden resistor installed
on copper plate was less than the case of aluminum plate.
We believe that this temperature compensator can control
the temperature of plate and inner air within 1.0 degree on
all condition.
2.2 Important parts1) DAC (Digital to Analog Converter)
DAC 701LH (unipoler) and DAC703LH (bipoler) arechosen. These DACs have good performance. However it
is not sufficient for us regarding temperature and drift
characteristic. We will select DACs that have small valueof the temperature coefficient (TC) less than 5 ppm/ °C.
After that, we will do burn-in for unipoler DACs to reduce
the long-term drift less than 30 ppm/ year. Consequently,
it is found to be not necessary to cool the surface of DAC
by attaching to the plate of temperature compensator(referring in Fig. 1).
2 )Error and Buffer Amplifiers
OP 27 are selected as operational amplifiers for error
and buffer amplifiers. The long-term drift of thisoperational amplifier is about 10 ppm/ year because
network resistors that have same characteristics will be
used to get rid of drift of the gain of the amplifiers.

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The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997

3) DCCT (Current Transformer for Direct Current)
DCCT transforms the current of power supply to lowcurrent, and the low current output is applied for input of
the burden resistor that set in temperature compensator.
DCCT has very small TC in principle except for thetransforming circuit from current to voltage. The longterm drift is less than a few ppm/ year. Two types of
DCCT are used for the power supplies. It is found one of
the types had peculiar ripple and no shield forelectromagnetic susceptibility (EMS) (4). Thus we have
let the makers to improve it.
4) Burden Resistor
This part is used for transforming the DCCT current tovoltage (max. l.OV). Therefore its temperature and current
characteristic are very important. Current characteristic is acharacteristic for resistance value versus input current.
The burden resistors that we use are specially made for us.
The change of resistance value is less than 20 ppm from 0
to full current (max. l.OA). Then the TC and long-term
stability are less than 5 ppm/ oc and less than 20 ppm/
year respectively.
5) Shunt Resistor
Shunt resistor is used to detect the current of a low
current power supply such as St magnet power supply. Itis difficult to make the current characteristic well, because
the input current is larger than the current of burden
resistor. Therefore we made the max. voltage lower (0.1 V)
to reduce the temperature rise of the resistor. The current
characteristic of 5A and lOA shunt became less than 20
ppm consequently. The shunt resistors are also used forbeam transport Q magnet power supplies of which max.
currents are 30, 50 and 100A. The current characteristic isless than 100 ppm. The long-term stability and TC ofthese shunt resistor is less than 100 ppm/ year and 5 ppm/C respectively.
6) Total Performance Including Temperature Compensator
As a result of the test of R&D power supplies, total
TC of the control unit proved to be less than 10 ppm/ °C.
Therefore if we use the temperature compensator, the driftcaused by temperature change (10 to 50°C) will be within
10 ppm/ year.
7) Gain and Offset Adjustment
We decided not to use trimmer such as variable resistor
for adjusting the gain and offset of power supply to savetrouble caused by adjustment and to reduce the long-termdrift. To adjust the gain and offset, we have introduced
digital adjustment that we call it double buffer method.
Total errors of gain and offset of all the parts are a few
percentages. However we can reduce its error to less than
50 ppm against a standard current monitor by the double
buffer method. This method is that the CPU of interfaceof power supply calculates the corrected set value {onregister 2) for DAC from the down loaded set one (onregister 1) by using the coefficients for correction stored in
the non-volatile memories of the interface.
2.3 Switching Mode Power Supply
Several switching mode power supplies made bydifferent makers had been tested for two years. In thisparagraph, we report the results.

I) Efficiency & Size
The efficiencies of three power supplies of whichpowers are 20kW (500A, 40V) are over 90 %. On theother hand two power supplies (±5A, ±60V) for St
magnets are less than 70 %.
The size of the smallest power supply is 480mm (w),590mm (H) and 600mm (D). Because 20kW class power
supplies are very small, we can set up two power suppli~sin one rack. The smallest St magnet power supply IS
480mm (w), 48mm (H) and 500mm (D). Then we can set
up 20 power supplies in one rack.
The switching frequency is important factor to makethe power supply small and light. The frequencies of
20kW power supplies are 20kHz except for one (5kHz).
The power supply of which frequency is 5kHz is about
twice bigger and heavier than the others and noisy because
the frequency is within hearing limit. On the other handthe frequencies of two St magnet power supplies are
100kHz and 50kHz. The switching frequencies of power
supplies for KEKB are 20kHz for the power supplies
above 20kW and 100kHz forSt magnet power supply.
2) Stability and Ripple
The stability of the prototype power supply (25kWclass) is about 20ppm/ 57 hours on condition that thecontrol circuit is in a thermostat, and the ripple is a few
ppm. About St magnet power supply made for R&D, thestability is 250ppm/ 87 hours on the same condition as
25kW class one, and the ripple is less than lOppm. Thepower supply (25kW class) is satisfied with ourrequirement, but there is room for improvement of theripple. St magnet power supply is not satisfied with ourrequirement for the stability, but it will be improved forKEKB.
3) EM/ (Electro-Magnetic Interference)
VCCI (Voluntary Control Council for Interference by
information technology equipment) class A (for industry)(5) has been adopted for magnet power supplies of KEKB.
A prototype power supply (25kw) for KEKB has cleared it
for radiated emission level easily. However for theconduction level, it has cleared its level after reinforcing
the AC line filter. On the other hand St magnet power
supplies have no problem.
2.4 ARCNET Interface
There is a communication controller for ARCNET anda CPU on the interface board to control a power supply. It
is same as a half size VME board, and its cost is about
17,000 yen. This will be installed into the front panel ofthe power supply. One port of the VME driver can drive
20 St magnet power supplies at maximum number.
Shielded cable (category 5) and connector (RJ 45) has been
introduced to protect the circuits from the electromagnetic
noise as a result of test. Then synchronized start trigger
pulses for all power supplies are distributed from VME
driver to interfaces through the same cable of the category
5. ARCNET and start trigger pulse signals arecommunicated to interfaces by pulse transformer andphoto coupler respectively, and the data transfer capabilityof ARCNET is 2.5Mbps. Therefore 15 St magnets can becontrolled synchronously within one second including thedata transfer and current setting.

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The II th Symposium on Accelerator Science and Technology, Harima Science Garden City, I997
Control Room
EthernetIJcloj~-- j_ ~~-xten er:vMEH Br - - - _I

A: VME-Sequence Control Interface
B: VME-ARCNET Interface
C: Start Signal Module
D: VME-GPIB Interface

IIII.

t

GPIB Bus

I_ Extender

UVM'-! :scanner
1l

Current Monitor
max. 21 nodes
IfF
Control Unit
Vemperature
Compensator·I -I I

I

Externalr-

Output Unit

Sequence Network
Emergency (D9)I-'~,AIIIII:SL

StartSigna

Jl-I B,QMag.

Lr
Sequence- I Controller

UVM~>canner

IfF

Output Unit

II B,QMag. I'"'1

ARCNET + Start SignallIfF
Control Unit
temperature
Compensator_j,nStart Trigger (TTL)

1~_;ontrol

Unit
OutputUnit

IfF
control
Unit
OutputUnit-f-I II SxMag.
B,QMag. I
I Magnet Interlock I Water Flow & Mag. Temp.

-I I

SxMag.

I

External Interlock

I Patrol Light I

Fig. 3 Block diagram of the KEKB magnet power supply system.

3 Power Supply System
3.1 Current Control
Fig. 3 shows a block diagram of the KEKB magnet
power supply system. There are two ways to control thecurrent of power supply roughly. One is a way of using
start trigger pulse, and the other is a way of using startcommand. Thus there are two ways of data creation forabove-mentioned ways. One is a way of using the linear
data calculated by CPU from present set value to target
value. The other is a way of using the data that is sentfrom VME driver and stored in the memory on theinterface. The current of St magnet will be controlled byusing the start trigger pulse and the data stored in thememory at COD correction.
3.2 Current Monitor System
As shown in Fig. 3, we use GPIB DVMs (DigitalVoltage Meter) and Scanners that are in a rack without airconditioner. All current data of power supplies can betaken within 1 or 2 seconds in case of low accuracy mode(error=0.02% ). The Accuracy of the current monitor
system depends on the accuracy of current monitor outputof power supplies and the accuracy of the DVM andscanner system. About the former, exact value of thecurrent can be obtained to use the coefficient of correction
for real current such as the double buffer adjustment. Thiscoefficient is stored in the non-volatile memory too.
When the long-term drift of gain and the coefficient ofcorrection of particular power supply will be measured,
the high accuracy mode of this system will be used.
3.3 Interlock System (Sequence Control System)
This system has a CPU in a main power supply room(D8) and fiber-optic ring to communicate with othersystem located in 7 power supply rooms, and this network
is self-healing type. As a measure against trouble, theCPU has two power supplies for its self.

3.4 Cost
Two things are introduced to reduce the cost of thepower supply system. One is providing the importantparts to the makers after the public tender. The other isseparation of the public tender to several parts such as
power supplies (large, middle and little power) current
monitor and interlock. As a result, the total cost has beenequall to the TRISTAN's, and we think that KEKB power
supply system has been made at its best.

4 conclusion
As a result of many R&D and the effort of reducing
the cost of the power supply system, the highperformance and low cost system will become anaccomplished fact. We will set up and adjust all thesystem from April to August in 1998. We think there
will be no trouble because the power supplies will betaken measures to meet EMC (Electro-MagneticCompatibility) (4) sufficiently.

References(1) T. Kubo et al., "Design of Magnet Power Supplies for
KEKB Accelerator", Proc. lOth Symposium on
Accelerator Science and Technology, October 1995,
pp118-120.
(2) K. Oide, "Method of Operation for KEKB Magnets",
KEK Internal Report, September 1995.
(3) "ARCNET Technical Manual, Rev. A", Toyo
Microsystems Co., August 1997.
(4) C. R. Paul, "Introduction to Electromagnetic
Compatibility", John Wiley & Sons, Inc., 1992.
(5) K. Ito, "Handbook for Measures of Electric Noise",
The Nikkan Kogyo Shinbun, Ltd., August 1994,
pp779-780.

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