Trigger-timing signal distribution system for
the KEK electron/positron injector linac
T. Suwada, 1 K. Furukawa, N. Kamikubota, and M. Satoh,
Accelerator Laboratory, High Energy Accelerator Research Organization (KEK),
1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

Abstract
The KEK electron/positron injector linac provides a short-pulse electron beam withan energy of 2.5 GeV for the Photon Factory (PF) storage ring, that with an energyof 3 GeV for the Advanced Ring (PF-AR) for pulse X-rays, and single-bunch electron
and positron beams with energies of 8 GeV and 3.5 GeV for the KEK B-Factory(KEKB) storage rings, respectively. A trigger-timing signal distribution system of
the injector linac was newly developed and extended for stable injection to the
KEKB rings with the required injection-timing accuracy highly stabilized to lessthan 30 ps in root mean square because the old trigger system distributed thetrigger-timing signals for the injection to the PF ring and the PF-AR with aninjection-timing accuracy of 300 ps. In this report the design and its performanceof the new trigger-timing signal distribution system are described in detail.
Key words: Trigger-timing signal distribution system; rf synchronization; Electronlinear accelerator
PACS: 29.17.+w, 29.27.Ac, 41.85.Ar

1

Introduction

The KEK electron/positron injector linac [1] injects a short-pulse electron
beam with a pulse width of 1 ns to the PF ring and the PF-AR once and threetimes in daily operation, respectively, and also injects single-bunch electron
and positron beams with a bunch width of ∼10 ps directly into the KEKB
rings [2] about twenty times in daily operation. The beam commissioning of
the KEKB started in 1997 for testing CP violation in the decay of neutral
1

Corresponding auther. E-mail address: tsuyoshi.suwada@kek.jp

Preprint submitted to Nucl. Instr. and Meth. in Phys. Res. A

6 October 2003

B mesons with an asymmetric electron-positron collider comprising 3.5-GeV
positron and 8-GeV electron rings.
The injector linac was upgraded for injection to the KEKB rings, which requires a precise trigger-timing control of the injector linac for more stable operation. One of the many items for the injector upgrade is the development of
an integrated trigger-timing signal distribution and its control system, whichhave been newly extended for performing stable injection to the KEKB rings
along with the existing trigger control system for injection to the PF ring and
PF-AR.
Thus, the injector linac has an injection system for the four storage rings, thatis, the PF ring, the PF-AR and the two KEKB rings, according to their various
operation modes for which the mode switch should be performed both rapidly
and stably more than fifty times in daily operation. The trigger-timing signal
distribution system provides trigger-timing signals for the pulsed operation of
two sets of electron guns and pre-injectors (one is for the PF and the PF-AR,and the other is for the KEKB), 59 acceleration rf units, rf monitors, beam
monitors, a pulsed focusing coil for positron generation, and other equipments.
The linac beam pulse should be synchronized with rf frequencies of the PF(500.1 MHz), the PF-AR (508.6 MHz) and the KEKB (508.9 MHz) in order
to inject a single rf bucket of each ring within an allowable timing jitter.
The existing trigger control system for the PF and the PF-AR has been alreadydescribed in detail previously [3,4]. Here, in this report, the new trigger-timing
signal distribution system, which has been developed and extended for the
KEKB operation, is described in detail along with the interrelation between
this new system and the existing trigger system.

2

Overview of the trigger-timing signal distribution system

The injector linac with an overall length of 600 m is partitioned into eight sectors. Additional three sectors (A, B and C) were newly extended for KEKB
operation in 1997, while five sectors (1-5) have already been used for PF and
PF-AR injection operation since 1982. Each sector corresponds to a basic
unit of an rf power distribution system. As following the rf power distribution system the trigger-timing signals are distributed from a main station toeight stations (sector stations) installed at the beginning of each sector (seeFig.1). The main station is installed close to the main control room of theinjector linac. It provides master-trigger signals to the sector stations, beamtiming signals to the electron guns, and injection-timing signals to septum
and kicker magnets according to the revolution frequency of the KEKB andPF (or PF-AR) rings. Each sector station receives the trigger-timing signal
2

and distributes it to a sub-booster klystron for its pulsed rf generation, to themodulator of the sub-booster klystron, to an rf pulse compression device [1],and to beam monitors and rf monitors for their timing of their data-acquisition
system. For KEKB injection operation, the first sector station (sector stationA) provides the trigger-timing signal to the operation of half of the rf-power
distribution unit and to the pre-injector system, which comprises an electron
gun, two sub-harmonic bunchers (SHBs) and a traveling-wave buncher. The
trigger-timing signal for high-voltage modulators of eight high-power klystrons
is directly distributed from each sector-control station, while it is regenerated
on the base of the trigger-timing signal sent from each sector station.

Fig. 1. Layout of the KEK electron/positron injector linac and the location of trigger
stations.

3

Trigger-timing signal distribution system

3.1 Clock generation and subharmonic frequencies
It is strongly required for its injection with an accuracy of 30 ps in root meansquare (r.m.s.) from the timing center of a ring’s rf bucket in order to suppress
any amplitude growth of synchrotron motion in the KEKB rings to be as small
as possible. This means that the trigger-timing signal distribution system of
the injector linac should be designed to synchronize accurately. For its synchronization accuracy, the injector linac needs to inject single-bunch electron
and positron beams to the KEKB rings with a common sub-harmonic frequency between the linac and the KEKB rings. The fundamental rf frequency
is 10.38546 MHz, which has a common harmonic number of 275 times for the
rf acceleration frequency (2856 MHz) for the injector linac and that of 49 times
for the KEKB rings (rf acceleration frequency 508.9±0.3 MHz). Thus, it is designed that the single-bunch beams need to be bunched by using two SHBs (rffrequencies of 114.24 MHz and 571.20 MHz) for which the two rf frequencies
3can be generated by the fundamental rf frequency. The relationship between
the fundamental and sub-harmonic rf frequencies for the injector linac and
the KEKB rings is shown in Table 3.1. These rf frequencies are generated andprovided by frequency-multiplying and frequency-dividing the fundamental rf
signal generated from a 571.2-MHz rf signal generator installed at a main rf
staton [5]. The fundamental rf frequency can possibly change the frequency
with a step of 0.1 Hz in order to correct the circumference particle-orbit lengthof the rings due to the temperature variation in the ring tunnel during a day.
The 571.2-MHz rf signal is also used as a clock signal in the trigger-timing
signal distribution system. This means that the trigger-timing step is variablewith a step of 1.75 ns.
Table 1
Fundamental and common rf frequency relationship between the injector linac and
the KEKB rings.
RF Device

Multiplication

RF Frequency [MHz]Fundamental-

10.38546

SHB1

×11

114.24SHB2

×55

571.20Linac Acceleration rf

×275

2856

KEKB-ring Acceleration rf

×49

508.8875

3.2 Trigger-timing signal generation at the main station
A block diagram of the trigger-timing signal generation in the main stationis shown in Fig.2. The maximum repetition rate (50 Hz) of the trigger pulse
is generated from a line-locked generator. It was designed to provide triggers at a fixed phase of the 50-Hz power-line frequency so as to stabilize the
klystron beam current heated by the 50-Hz power line and the function of acharging unit for a high-power klystron modulator. The trigger pulse is thensynchronized by a trigger synchronizer with a bucket-selected trigger pulse of
the ring through the KEKB bucket selection system [6]. The bucket-selected
trigger pulse is generated with a maximum delay time of 500 µs after the
linac line-locked trigger by synchronizing with the ring’s revolution frequency(2.03 kHz). It is derived by dividing the fundamental frequency by the harmonic number (h=5120) of the KEKB rings, while it is synchronized by therevolution frequency of 1.6 MHz for the PF (or 0.8 MHz for the PF-AR).
An injection mode selector switch selects the operation mode required by anoperator through the linac control system [7]. Each trigger synchronizer gen4

erates basically three kinds of the trigger-timing signals. These are a mastertrigger, a kicker trigger to each ring, and a trigger to a grid pulser of the electron gun for which the trigger timing is controllable by using a 16-bit digitaltime-delay module (TD-4) [8] through a CAMAC-based control system. The
time-delay module is a single-width CAMAC module which counts a 571.2MHz clock signal by a D-type flip-flop with a 16-bit presettable BCD counter
with high speed integrated emitter-coupled-logic (ECL) circuits. It generates
a delayed trigger pulse synchronized with the 571.2-MHz rf. The maximum
delay is about 115 µs in steps of 1.75 ns, and its maxmum clock frequency isavailable up to about 720 MHz. The jitter of the output pulse is less than 3 ps
in r.m.s. The master trigger is sent to a trigger transmitter module where themaster trigger signal is regenerated by combining 571.2-MHz rf and a monocycle signal generated by a monocycle pulse generator with fine adjusting of therelative phase. In the transmitter module the power level of the 571.2-MHz rf
is amplified to the level of 36 dBm (or 4W ) from the input level of 10 dBm,
where the power level is stabilized within 1% by an amplitude gain controller(AGC), and the phase is well stabilized within 3 ps in r.m.s. by a phase-locked
loop (PLL). The jitter measurement result is shown in Fig.3, where the phasejitter of the 571.2-MHz rf was measured by detecting its zero-cross signal jitter. A signal picture of the master trigger signal is shown in Fig.4. The trigger
transmitter sends the master trigger signals to sector stations A, B and C,
and also to sector stations 1-5 through coaxial cables (diameter of 30 mm)
with low loss and good phase stability (WF-H50-7S, Mitsubishi cable industries, LTD.[9]). The relative timing chart of the generated trigger pulses andrf signals for the KEKB is summarized in Fig.5.

Trigger Transmitter

Main RF Station
x7

x7

x11

x7

114.24MHz

x5
571.2MHzto SHB1 to SHB2

2856MHz10.385MHz
Fundamental
RF

Phase AGC
Variable
Shifter
Attenuator
Amp508.888MHz

to Sector Station ABC

RF
Combinerto Sector Station 1 5
RFCombiner

PLL
Variable
Phase Shifter

to Linacto Ring

SectorStationGrid Pulser(KEKB)A

Main Station
114.24MHz

1/h Harmonic Number (h=5120)
frev(2.03kHz)
Line-Locked
50Hz
1/N

10.385MHz
Delay

114.24MHz
Delay

Master Trigger

Monocycle
Pulser

SectorStation1

571.2MHz(KEKB)

571.2MHz
TD-4 Delay

Synchronizer(PF-AR or PF)

Sub-control
StationRing Kicker(KEKB)

A

Selector
Grid Pulser(PF-AR or PF)
Ring Kicker(PF-AR or PF)

DoubleSynchronizer

Sub-control
Station1

frev(0.8MHz/PF-AR)or frev(1.6MHz/PF)
114.24MHz

Fig. 2. Block diagram of the trigger-timing signal generation in the main station.

5

10ps/div

Fig. 3. Phase-jitter measurement result of the master trigger in the main station.
The digital signal shows the phase jitter of the zero-cross level for the 571.2 MHz
rf.

5ns/div
1V/divFig. 4. Master trigger signal generated in the transmitter module.

Line-Locked 50Hz
Bucket Selection

0 ~ 500µs

2856MHz571.20MHz
114.24MHz
508.88MHz
Gun Grid Pulser
Master Trigger
Ring Kicker/Septum

Fig. 5. Relative timing chart of the generated trigger pulses and rf signals for KEKB
operation.

6

3.3 Trigger-timing signal distribution at the sector station
A block diagram of the trigger-timing signal distribution in the sector stationis shown in Fig.6. The transmitted master trigger is picked up by a directional
coupler with a coupling strength of 16 to 20 dB, depending on the locationof each sector station. The master trigger with an rf power level of about
12 dBm is sent to a trigger receiver module installed at each sector station. A
trigger-timing one-shot signal (NIM standard) is generated by detecting thepositive leading edge of the monocycle trigger signal with a voltage discriminator circuit in the trigger receiver module. This signal is used for a startpulse of the time-delay module. On the other hand, the 571.2-MHz rf is regenerated from the master trigger signal through a 571.2-MHz bandpass filter inthe trigger receiver module. This rf is distributed as a clock signal of the delay
module. Thus, the trigger-timing signals are regenerated for the pulsed rf andhigh-voltage generation of the sub-booster klystron as well as the phase flip
timing for the rf pulse compression device, for the high-voltage generation of
the positron pulse modulator, and for the rf monitors and the beam monitors
according to preset digital time delays in each sector station.
On the other hand, the trigger-timing signals for eight high-power klystron
modulators are regenerated and distributed in each sector-control station
placed at the center of each sector, except for a common sector control station
for the new sectors (A, B and C). The trigger receiver module sends the 571.2MHz rf clock and trigger signals directly to the sector control station throughcoaxial cables, where similar 16-bit digital time-delay modules (TD-4V) arecontrolled through a VME-based control system. The specification of the TD4V module is almost the same as that of the TD-4 module, except for its
control interface. This module was historically developed as a CAMAC-based
module, while the VME-based control system became a standard interface
towards the upgrade to the KEKB operation in the injector linac.

3.4 Control software
The control of the timing system is a part of the integrated linac control system. It is based on the multi-layer architecture, in which lower layer servers
support each different hardware, and upper layer servers are designed to provide hardware-independent services to the application layer [7]. The timing
control is named as “trig” and upper layer server is called “rtrigd”. Rtrigd
serves various timing related functions to the application layer through TCPbased remote procedure calls (RPC), while it communicates with several different lower-layer servers, such as for CAMAC-based TD-4 and VME-based
TD-4V, via UDP-based RPC.
7

to Sector Station ABC

Trigger
Transmitterto Sector Station 1-5

Sector Control Station 1

Sector Station 1
Clock

Trigger
Buffer Fan Out
NIM

Trigger Receiver
Trigger

Trigger

Clock571.2MHz
TD-4 Delay

to Sub-booster rf
Clock571.2MHz
TD-4V Delay

571.2MHz
TD-4 Delay

to Sub-booster
Modulator
Clock571.2MHz
TD-4V Delay

571.2MHz
TD-4 Delay
571.2MHz
TD-4 Delay

Clock Distributor
Clock
Clock

Clock

Klystron
Modulator 2
Klystron
Modulator 3

571.2MHz
TD-4V Delay
Clock

Klystron
Modulator 1

Clock

to rf Monitors

571.2MHz
TD-4V Delay

Klystron
Modulator 8

Fig. 6. Block diagram of the trigger-timing signal distribution in the sector stationand the sector-control station.

The common application software is used for the routine operation and for the
optimization of beams, which includes a beam mode switch panel, a parametersave-restore panel, active and passive correlation plots, beam and device feedback systems. Device specific application panels are also used by operators.
They all provide the basis of the stable linac operation. Furthermore they are
essential to operate on the positron injection to KEKB with two bunches in apulse since the two-bunch beam is sensitive to its timing [10].

4Performance of the new trigger-timing signal distribution system

The performance of the new trigger system was tested by measuring the timing
jitter of the trigger signal generated at all the sector stations with a digital
sampling oscilloscope with a frequency band of 20 GHz. The trigger pulse andthe rf clock regenerated in each sector station were returned back to the main
station by using similar coaxial cables in order to measure their timing andphase jitter. The measurement result is shown in Fig.7. The result shows thatthe maximum timing jitter of the trigger pulse regenerated from the sector
station 5 was less than 5 ps in r.m.s., while the timing jitter of the trigger
pulse from other sectors was less than 4 ps in r.m.s. They were measured by8

detecting the zero-cross signal jitter of the rf clock in the main station withthe trigger pulse coming from each sector station. The result is sufficiently
satisfied with the required injection-timing accuracy for the KEKB rings.

10ps/div

Fig. 7. Timing jitter measurement result of the trigger signal generated at sector 5.
The digital signal shows the phase jitter of the zero-cross level for the 571.2-MHz
rf.

The new trigger system was also tested by measuring a single-bunch structure
at the outlet of the pre-injector with an optical transition radiation monitor
with a streak camera system [11]. The result is shown in Fig.8. The full widthat half maximum is about 7.1 ps, where the bunch width is strongly dependentof the beam-timing accuracy for the electron gun, the trigger-timing accuracy
for the streak camera and the relative timing accuracy between the bunch andthe acceleration phase. This measured bunch width is very consistent witha simulation result based on the beam dynamics at the pre-injector within
the measurement error. It should be emphasized that the new trigger-timing
system of the injector linac works very well under the condition for KEKB
operation.

5

Conclusions

A new trigger-timing signal distribution system was developed for KEKB operation at the KEK electron/positron injector linac. The new system was
extended from the existing trigger control system with its good extensibility
and flexibility. The jitter measurement of this system shows that the specification for the injection accuracy within 30 ps in root mean square is sufficiently
satisfied for both the single-bunch electron and positron beams to the KEKB
rings. The new trigger system has been working well along with the existing
trigger-timing system for the PF and the PF-AR since the start of the KEKB
commissioning in 1997.
9

Intensity [arb. unit]

7.1 ps (FWHM)

Time [ns]Fig. 8. Single-bunch structure of an electron beam measured by an optical transition
radiation monitor at the pre-injector.

Acknowledgements
The authors are very grateful to Dr. T. Urano for his contributions to thedesign and construction of the trigger-timing and its control system in theinjector linac as our previous group leader.

References[1] I. Abe et al., Nucl. Instr. and Meth. A 499 (2003) 167.
[2] S. Kurokawa and E. Kikutani, Nucl. Instr. and Meth. A 499 (2003) 1.
[3] T. Urano and K. Nakahara, Nucl. Instr. and Meth. A 247 (1986) 226.
[4] T. Urano, Y. Hosono and K. Hasegawa, Nucl. Instr. and Meth. A 327 (1993)
529.
[5] H. Hanaki, S. Anami, S. Fukuda, H. Katagiri, T. Matsumoto and S. Michizono,
Proc. First Asian Particle Accelerator Conf. (APAC’98), KEK, Tsukuba,
Japan, 1998, p. 139.
[6] E. Kikutani, Y. Ogawa and M. Tobiyama, Proc. the Second Asian Particle
Accelerator Conference (APAC2001), Beijin, China, September 17-21, 2001,
p. 669.

10

[7] K. Furukawa, N. Kamikubota, T. Suwada, and T. Urano, Proc. the Int l Conf.
on Accelerator and Large Experimental Physics Control Systems (ICALEPCS99), Trieste, Italy, Oct. 4-8, 1999, p. 98.
[8] Private communication from M. Tobiyama.
[9] Mitsubishi Cable Industries LTD., 4-1 Marunouchi, chiyoda-ku, Tokyo 1008303, Japan.
[10] K. Furukawa, N. Kamikubota, T. Suwada and T. Obata, Proc. the Int
l Conf. on Accelerator and Large Experimental Physics Control Systems(ICALEPCS2001), San Jose, U.S.A., Nov. 27-30, 2001, p. 266.
[11] Y. Ogawa et al., Proc. the First Asian Particle Accelerator Conf. (APAC 98),
KEK, Tsukuba, Japan, 1998, p. 534.

11