Timing system of the ATF
T. Naito, H. Hayano, T. Korhonen, S. Takeda, J.Urakawa,KEK, High Energy Accelerator Organization, 1-1 Oho Tsukuba, Ibaraki, Japan 305

Abstractbunch and the damped beam is extracted sequentiallyafter several damping time.

A timing system was constructed for Accelerator Test
Facility(ATF) for future linear collider R&D at KEK.
The operation of the ATF has several features, forexample, multi-bunch
acceleration, delta-f energy
compensation, multi-train storage, etc.. The timing
system provides synchronized reference signals andtrigger signals for each hardware. To keep stable phaserelationships at each component, the reference signals of
acceleration frequencies are transferred directly byusing phase stabilized optical transfer lines. The beamtiming is adjusted with the synchronized delay modules
which used ECL preset counter circuits. A bucket
selector circuit and a bucket matching circuit are used
for manipulation of the beams in the damping ring.
CAMAC interfaces and Vsystem for programming wereused for control. The hardware performance and thesoftware environment are described.
1 Introduction
The ATF consists of a 1.5GeV S-band linac, a dampingring(DR) and an extraction section for diagnostics of thedamped beam characteristics. The linac accelerates
multi-bunch beam which has 20 bunches of 2x1010
electrons with 2.8ns bunch spacing and the repetition
rate is 25Hz. The energy spread of the multi-bunch
beam is required to be less than 1% for the DR injection.
The DR stores muti-train(max. 5 trains) of the multiPLL Control

Master Osc.
714MHzHP8644A

Ramp Generator

Beam Trigger

Phase Shifter

DeviceFrequency(MHz)Master Osc.
1428
LinacAcc. Structure2856ECS Structure
2856+/-4.32
SHB,Gun grid357
Damping Ring
RF cavity
714
Revolution
2.16
Table 1 Devices and the used frequencies
The timing system generates both the reference
signals for each hardware which use different frequency
and trigger signals for pulsed devices which use different
repetition rate. The device and the used frequencies aresummarized in table1. All of the reference signals andthe trigger signals are required to be preciselysynchronized. The accuracy and stability are significant
issues in the accelerator performance. The generated
signals have to be distributed to each location of over
100m, without deteriorating of the quality. An opticaltransfer system by using phase stabilized optical fiber
was used for the delivery of signals. The operationmode, for example, the beam and the pulsed RF timing
selection, the injection/extraction timing selection, thebucket selection of the DR and the number of the train
selection of the DR, is manipulated by changing thephase of the timing circuits.
2 Hardware scheme

Phase Detector
Reference Clo

x2 Multiplier
2856MHz

Master Osc.
1428MHz
10kHz
reference

2.1 Reference signal generation

x1/2 DividerHP8663A

714MHz
Reference Clo

BucketSelector

x1/2 Divider
357MHz

SSB signal
Generator

x2 Multiplier
4.2MHzx1/165 Divider
2.1MHzGun Trigger
Circuit

E/O

Reference Clock 2.1MHz

E/O

Reference Clock 357MHz

E/O

2856MHz

Amp.

Amp.

SHB

SHB

O/E

GunB

Fig. 1 Scheme of the reference signal generati

The scheme of the reference signal generation anddistribution is shown in fig. 1. The half of theacceleration frequency(1428MHz) was selected toreduce the number of the divider and the multiplier andto use the stabilize frequency range of the masteroscillator. The jitter among each frequency ought to bereduced using only several dividers and multipliers.
The linac uses 357MHz for an electron gun grid
driver and two sub-harmonic bunchers, 2857MHz for abuncher and nine klystrons and 2856MHz+/-4MHz for
two klystrons of the energy compensation system(delta-fECS)[1]. In order to suppress the energy spread of themulti-bunch beam which comes from the transient beamloading effect, the slightly different cavity frequencies of2856MHz+/-4MHz are used. The phases of the delta-f
ECS are required to synchronize the revolution of theDR. The DR operates with the cavity frequency:
714MHz, the revolution frequency: 2.16MHz and theHarmonics number: 330.
The time jitter of the multiplier/divider wasmeasured by a sampling scope(HP54129B). The
relative time jitter from 2856MHz to 714MHz and357MHz were 0.85ps and 0.71ps, respectively. Thesevalues are enough to the linac stable operation. The time
jitter of the ECS frequency(2856MHz+/-4MHz) was0.8ps.[2]100Conventional fiber cable

8060

4020
Phase stabilized fiber cable

2.2 Trigger signal generation
The trigger signals are made from the synchronizedsignal of AC power line(50Hz). The advantage ofsynchronized signal of AC power line is the reduction of
the fluctuation of the high power devices. The repetition
rate can be changed from 50Hz to 0.39Hz by the control
computer. Different repetition rate can be selectedindividually for each device. The trigger signals are alsosynchronized by the revolution freq.(2.16MHz) and theSHB freq.(357MHz) for synchronization of the all RFdevices. The time delay among the devices is created by
the synchronous and delay counter module(called TD2)
developed at TRISTAN timing system. The time delay
can be adjustable with 2.8ns step. The improved version
can count up to 1.4GHz and the time jitter is ~5ps(σ) at714MHz clock. [3]2.3 The optical transfer system
The drive signal of linacs have been distributed by using
the coaxial cable. The down converted frequency wasused for reduction of the power loss and reconverted to2856MHz at each location. The coaxial cable is not sostable against the temperature change. At the ATF, there
is no air conditioner at the klystron station. Thetemperature stability is one of the serious problems. The
optical transfer system was used for distribution of thereference signal and the trigger signal by using the phasestabilized optical fiber cable. The optical fiber(SUMITOMO DTS) has a very low temperature
coefficient(0.04ppm/ °C ).
Thetemperature
characteristics are shown in fig. 2. 3510A(transmitter)and 4511A(receiver) (Ortel Co.) were employed while
the E/O and O/E for 2856MHz direct distribution, thetemperature coefficients 0.45ps/ °C and 0.85ps/ °C ,respectively, were measured. The phase variation at theactual station in a day was measured less than 10degree(10ps). The time jitter of the optical transfersystem, when 100m fiber cable was used, was 0.7ps.

0-20-200204060

Temperature[degree]
Fig.2 Temperature dependence of the phase stabilized fiber

2.4 Bucket selector
The selection of the bucket of the DR is done bychanging the relative phase of the DR revolution and thebeam timing of the linac. The bucket selector consists of
two TD2’s, one is for selection of the bucket number andthe other is for the bucket matching described in the later
section. The TD2’s are connected cascade and shift thephase of 2.16MHz with 1.4ns step by counting 714MHz.
In order to keep same phase of the delta-f of the ECS atevery injection timing, the twice of the output of thebucket selector, 4.32MHz, is used. In case of 5 trains
injection/extraction mode, the bucket selector has tochange the timing in each injection interval of 40ms.
The local control and auxiliary crate controller interface
with a personal computer(LACC) are used for thispurpose. The accelerator control system could notguarantee the access interval within less than 40ms. TheLACC can change the value of the delay counter of theTD2 within ~1ms. The performance is not yet tested atthe operation.
2.5 Bucket matching
There is a requirement to shift the frequency of the RF
cavity of the DR, for example, in case of the dispersion
measurement. The second oscillator is used for thispurpose. The two frequencies of the master oscillator
and the second oscillator are in phase locked loop(PLL)at the normal operation. The dispersion measurement
procedure is following, 1)the PLL is turned off, 2)shift
the frequency of the second oscillator,. 3)measure theorbit, 4)return to same frequency, 5)the PLL is turned
on. The revolution phase of the DR is not same after theprocess. The bucket matching circuit is required to readjust the phase. The scheme of the bucket matchingcircuit is shown in fig. 3. The circuit counts both thefrequency of the oscillators individually when the PLL isturned off. The difference of the counters is calculated
and restore to the bucket selector after the PLL turned

on. The same LACC is used for the calculation and set
the data. Different scheme was used at TRISTAN byusing a phase detector and a phase shifter.[4] Theadvantage of the ATF bucket matching circuits are noshifting the frequency of the oscillator and a simple
configuration.

5 ACKNOWLEDGMENTS
We would like to express our thanks to Professors
M.Kihara and K.Takata for their encouragement. We
also wish to thank ATF operation group for usefuldiscussion.

3 Control environment
The control system is based on CAMAC andVAX(VMS) cluster system. The data base and GUI weremade by Vsystem.[5] It has many tools to ease control ofthe components. The some timing devices need to fineadjustment to reach the optimum timing. A convenient
control windows were made by Vsystem. Several
windows were already made for the timing devices, forexample, the repetition rate, the delay timing of thelinac, the DR, etc.. The timing control is also used as
the energy feedback at the linac. The one of theklystrons is used for compensate the energy drift bycontrolling the timing between the pulsed RF and thebeam. The energy of beam is controlled by using thedifferent timing of the rising edge of the pulsed RF. This
feedback is a operation within a few second range. A
part of the timing devices like the bucket selector byusing LACC is a shot by shot operation.

4 summary
The timing system of the ATF has been constructed
and confirmed the performance. The stability and theeasy tuning were confirmed by the commissioning of
the DR with the single bunch operation.[6] The multibunch operation is scheduled at early 1998. The opticalsignal distribution is promising for long distance andstable signal transfer as the linear collider reference line.
The R&D of X band (11.4GHz) transfer system is inprogress.

714MHzMaster Osc.

10 bit counter
NIM to TTL

PLLSecond Osc.

10 bit counter
714MHz

NIM to TTLBA

PLL on/OFF status

LACC

A-B

Bucket selector

Fig. 3 Bucket matching circuit

REFERENCES[1] J.Urakawa, et. al., “Gun trigger system for theATF”, NIM A 352(1994) 207-209[2] T.Korhonen et. al., “R&D OF THE TIMINGSYSTEM”, Poc. of Linac Conf. ‘94(p831) Tsukuba
Japan[3] T.Korhonen et. al., “Performance Evaluation of aHigh Bandwidth Timing Module”, KEK Internal,
96-3, 1996
[4] M.Kikuchi et. al., “BUCKET SELECTOR AND
TRANSFER TIMING IN TRISTAN”, Proc. of the
6th symp. of Acc. Sci. and Tec., p230 1987
[5] N.Terunuma et. al., “Status of the ATF controlsystem” ibd.
[6] H.Hayano et. al., “ Commissioning of ATF
Damping Ring”, Proc. of the 11th symp. of Acc.
Sci. and Tec., p68 1997