Synchronization scheme for the KEKB accelerator
T. Naito, J. Odagiri, M. Suetake, N. Yamamoto and T. Katoh
KEK, High Energy Accelerator Organization, 1-1 Oho Tsukuba, Ibaraki, Japan 305

Abstract

system is based on EPICS(Experimental Physics andIndustrial Control System) tool kits and uses large
number of IOCs(Input/Output Controllers) which are
distributed to each local station.[1]The timing system is classified into fast timing
signals and software timing signals. The fast timing
means the synchronized signal which is created by thehardware
directly,forexample,
rf(508MHz),revolution(100kHz), injection(50Hz), etc.. There will be
used many kinds of diagnostics tools and feedback
systems in the KEKB accelerator, for example, bunch bybunch beam feedback, laser wire, streak camera, wire
scanner, single shot BPMs, rf feedback, etc.. The
diagnostics tools and the feedback systems need to thebeam timing at each location. The fast timing signals are
created at the Center Control Room(CCR) and the linac
control room. The signals have to be distributed to all of
the local stations with high stability.
The software timing means the synchronized signal
which is created by the software. The timing signals areused for synchronizing each device under the differentIOCs. The timing signals are required to resolve theinjection timing(linac and BT) or the revolution
timing(rings). Many kind of the software timing arerequired. Several tasks are already reserved. In order toThe design of the synchronization system of the KEKB
accelerator is described. The synchronization system isclassified into 1)fast timing and 2)software timing. The
fast timing signals including rf frequency will be
distributed by a optical transfer system with a phasestabilized optical fiber. The performance has beenevaluated. A scheme of synchronization for multi-CPU
control is proposed as the software timing signal
generation and distribution. More than several tens ofcrates of VME and CAMAC will be used in the control
system. Each CPU will be located at each station along
the linac, the Beam Transport Line and the Rings andwill be connected with Ethernet each other. The
synchronization of the hardware under the different
CPUs
is essentialfor the precise control andmeasurement.

1 Introduction
The KEKB accelerator complex consists of a linac, theBeam Transport, the 8GeV High Energy Ring(HER) forelectron beam storage and the 3.5GeV Low EnergyRing(LER) for positron beam storage. The control®¯ÉÀ´Á®¯ÏÍÉÉÏÏ®¯ÉÀµÑ¶ÉÀ³Á¶¶ÉÀ²ÍÉÉÑÏ

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Fig.1 Timing signal distribution of the KEKB accelerator°ÉÀ®

reduce the hardware cost, the signal is submitted as thecode and decoded the code at each station. There areover 20 local control stations which are located aroundthe 3 km circumference ring.

2 Hardware of the fast timing signal
The fast timing signal means hardware driven
signals including the rf(508MHz) reference signal. The
fast timing signals are classified the high precision
signals and the other signals. The phase stability of thehigh precision timing needs to be less than 30ps and theother timing signals are required to resolve therevolution period, into less than 10micro-sec.

2.2 Distribution of the other timing signals
Some devices are required to transmit/receive thespecial timing signals. These signals are vertical kicker
timing, beam feedback request/status, beam abort
request/status, beam loss status, etc.. The timing signals
are required to resolve the revolution period into lessthan 10micro-sec. These signals are distributed by asimple fiber optic link. These signals are required toguarantee the time deviation from the source to thedestination.
HP54120B Sampling Scope

2.1 Distribution of the high precision timing signals
In order to resolve bunch by bunch beam timing,
following four signals are required at each local control
station,1)rf(508MHz),
2)revolution(100kHz),3)injection timing of the electron beam(50Hz or lowerrate) and 4)injection timing of the positron beam(50Hzor lower rate). The phase stability of the signal needs tobe ~30ps at the temperature range of 0 to 30 oC. An
optical transfer system with phase stabilized opticalfiber(PSOF) will be used to distribute these signals. The
optical fiber (SUMITOMO DTS) has a very low
temperature coefficient(0.04ppm/ oC). At the station in
the short distance, 200m or less, the PSOF can keep thephase stability without feedback. The distribution line
and each station are shown in Fig.1. The E/O and O/E
were evaluatedat 3510A(transmitter) and4512A(receiver) (Ortel Co.) which have the temperature
coefficients 0.45ps/ oC and 0.85ps/ oC, respectively. The
short time jitter of the optical transfer system, when
100m fiber cable was used, was 1.1ps for 508MHz. The
measurement set up and result are shown in Fig.2. Thetotal performance of the PSOF was confirmed atATF.[2]It is difficult to keep the phase stability without thefeedback system at the all location even if the PSOF isused. The longest distance from the CCR to the station isabout 2 km. Eight of the rf stations(D1~D11) have thephase locked loop feedback system with coaxial cables
and the phase stability keeps ~5ps. The coaxial cable
will be replaced by the PSOF with the feedback. The
feedback system is now under testing. [3]For the other signals except for rf, the phasestability and the time delay between the stations areadjusted by the synchronous
delay countermodule(called TD2) developed at TRISTAN timingsystem. The time delay is adjustable when 2ns step at508MHz clock is used. The improved version can countup to 1.4GHz and the time jitter is ~5.8ps(σ) at 508MHz
clock.[4]508MHz

Trg.

S.G.
100m Optical Cable
E/O
Ortel 3510A
O/E

sigma=1.1ps

Ortel 4512A

Fig. 2 Measurement of the short time jitter ofthe E/O, O/E system

3 Software timing signal
The software driven timing signals are required for
multi-CPU control system like the KEKB. The dataacquisition and the controls are required to synchronize
the injection timing or the revolution timing. The
command through the network can not guarantee thetiming. One network command or channel accessrequires 5~10ms even if there is no traffic. At the case of
the turn by turn beam position monitor(BPM), the IOCs
located in 20 different buildings which acquire the sameturn of the signals. It is required to have the hardware
which guarantees the synchronized timing with theinjection(50Hz) or the revolution(10micro-sec). Thissystem will be used at 1)synchronized data setting of thesteer magnets for the orbit change, 2)synchronized dataacquisition of the BPM at the linac and BT,3)synchronized data acquisition of the turn-by-turn BPM
at HER/LER and so on.

Computer Networkand the development of the control software are inprogress.

To Hardware Device

TimingIOC

5 Acknowledgments
Dealy(0~10µs)

16bit
Decoder
Revlution
TAXIchip
E/O

O/E

Inj.Trg.
50Hz

TAXIchipSet data

We would like to express our thanks to Professors
M.Kihara and S.Kurokawa for their encouragement. We
also wish to thank to commissioning group for various
discussion.

E/O

Transmitter module

To next station

Receiver module

Fig. 3 Software timing generation sheme

3.1 Generation of the software driven timing signal
The configuration is shown in Fig.2. In order to reducethe cost of the transfer line, the signal is submitted as the16 bit code. The transfer line is connected with an
optical fiber link. The submitted timing is synchronizedwith the injection timing or the revolution timing. Eachtask has own code and the signal is recognized at eachlocation with comparing the code and the device ID
value. The software sequence is following, 1)themanager IOC of the hardware checks the status of eachIOC, 2)the manager IOC requests the timing signal to
the timing IOC when all IOCs are ready, 3)the timing
IOC writes the code to the register of the transfermodule, 4)the code is transferred to all of the location
and recognized at the required station, 5)the code isconverted to a pulse and used as the timing signal after
adjusting the cable delay. The number of the code isextended easily for flexible use.
3.2 Hardware of the transmitter/receiver module
A pair of TAXIchip(Transparent Asynchronous Xmitter
receiverInterface,
Am7968(transmitter)/Am7969(receiver)) is used for theparallel to serial conversion and serial to parallel
conversion. Two Am7968s are used in the transmitter forswitching the transfer data of the injection timing andthe revolution timing, alternatively. The specified
transfer rate is 4Mbyte/sec to 12.5Mbyte/sec. There is atime
jittercomingfrom
theasynchronous
communication which is 10ns to 25ns. It is correspond toless than 1% of the revolution period. The performanceis under testing with the proto-type module.

4 Summary
The timing system of the KEKB accelerator has
been presented. The PSOF system will be achieved by
the requirement of the stability for the fast timing. Thesoftware timing with inexpensive and flexible system
has been designed. The confirmation of the performance

REFERENCES[1] T.Katoh et al., “Present status of the KEKB Control
System”, in these proceedings..
[2] T.Naito et al., ‘Timing system of the ATF”, in theseproceedings..
[3] E.Peschardt et al., “Phase compensated Fiber-optic
links for the LEP reference distribution”, Proc. ofPar. Acc. Conf. March1989, Chicago[4] T.Korhonen et. al., “Performance Evaluation of aHIgh Bandwidth Timing Module”, KEK Internal,96-3, 1996