DEVELOPMENT AND APPLICATION OF THE TRIGGER TIMINGWATCHDOG SYSTEM IN KEK ELECTRON/POSITRON LINAC
M. Satoh#, F. Miyahara, T. Suwada, and K. Furukawa
Accelerator Laboratory, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, JapanT. Kudou and S. Kusano
Mitsubishi Electric System & Service Co., Ltd, 2-8-8 Umezono, Tsukuba, Ibaraki 305-0045, Japan
Abstract
The KEK injector linac provides the different flavors ofelectron and positron beams to four independent storagerings. The linac beam is injected into the selected storage
ring in every time interval of 20 ms since the linac
parameters including timing and low-level rf phase can bearbitrary changed up to 50 Hz for the simultaneous top-up
injection of three rings. For the achievement of such
simultaneous top-up injection, a new event-based timing
and control system has been built to change the timing
parameters of various linac components less than 20 ms[1]. The components are situated over a 600-m-long linac,
and around 200 timing parameters should be stablychanged during the long-term beam operation. The newtiming system has been operated successfully since theautumn of 2008 and continuously improved upon by amodification of control software. Toward SuperKEKB
project, the linac timing watchdog and alert systems are
getting important for a day-to-day beam operation since
the high available operation system is strongly required.
For this purpose, we develop and utilize the several
timing watchdog systems. In this paper, we present thedetail of timing signal watchdog system for the KEK
injector linac in detail.

INTRODUCTION
The linac beam control system comprises the server
computers and several front-end computers. Each of themis connected via 1 Gigabit Ethernet control network. In
this decade, the server computers have been replaced by aLinux-based one from a Tru64 Unix-based one because ofmaintenance issue. The original linac control system has
been developed by using in-house software libraries
based-on the remote procedure calls (RPC). The client
user interface has been designed by Tcl/Tk scripts foraccelerating software development.
After the KEKB project launched, the linac control
system has been upgraded to the framework based-on theExperimental Physics and Industrial Control (EPICS)
system to improve the affinity between the ring control
systems. For the archiving of around 35000 parameters,
both of EPICS Channel Archiver [2] and Control System
Studio (CSS) Archiver [3] have been implemented for thelinac beam operation. In addition, the newly developedclient softwares are designed by Python scripting
language for the easy development.
These improvements make it easy to analyze thecorrelations between the linac and ring parameters. Such___________________________________________#masanori.satoh@kek.jp.

analysis is useful to identify the source of injection ratedeterioration and so on. Toward SuperKEKB project, thereliability of the timing system together with that ofcontrol system is getting important to increase the beam
operation availability. For this purpose, the developmentof the robust timing system is strongly desired. Inaddition, the development of excellent timing watchdog
system is also important. It can be helpful to find out thesource of timing system failure and fix it.

TIMING SYSTEM
Original Timing System
The maximum beam repetition rate is 50Hz limited by
the modulators of high-power rf system. A 50 Hz
monocycle pulse with a width of 1 ns and the 571.2 MHz
clock of about 36 dBm are combined in a trigger
transmitter module at the main timing station [4]. The
superposition waveform of the 50 Hz timing and the571.2 MHz clock signals is transmitted through a 30-D
coaxial cable as shown in Fig. 1. The output power levelis stabilized within 1% by an amplitude gain controller,
and the phase is well stabilized within 3 ps (rms) by aphase-locked loop. This signal is divided and distributed
to the each of the local timing stations with a low loss andgood phase stability. At the each local station, the trigger
receiver module decouples this signal into the 571.2 MHz
clock and 50 Hz timing signals. The 50 Hz timing signal
is finally fed to the modulator of high-power klystronafter applying a suitable amount of delay by a delay
module.
The timing signals with different amounts of delays are
generated at the local timing stations. The timing delay

Figure 1: Output waveform of trigger transmitter module.
The 50 Hz timing signal is superimposed on 571.2 MHz
clock signal.

modules called TD4V, TD4, and TD4R are based on theVME, CAMAC, and RS232C interfaces, respectively. In
these modules, an ECL counter of 16 bit can delay theinput signal up to around 114 μs in steps of 1.75 s, andits timing jitter is about 3 ps (rms). The intended use andthe number of modules are summarized in Table 1.
The software for the timing signal control is based onclient/server architecture to encapsulate the hardware
differences from the client applications. The control
command setting the delay on the client side is provided
to the each module through the RPC layer. The linac
operators can easily change the delay settings to theoptimized ones through the command line or graphicaluser interface (GUI). Though the integrated linac timing
system has been stably utilized for the daily beam
operation, the timing system upgrade was required for thesimultaneous top-up operation.

Event-based Timing System
Table 1: Timing delay modules of original system.
Location

Electrongun

Local
timingstation

TD4R

Main
timingstation/Sub-booster
TD4

Delay
moduleInterface# ofmodules
Intendeduse

RS232C
1

CAMAC
108

VME
63

e- beamtimingHighpower/subbooster
klystron,Low-level
rf, beam
monitortimingHigh powerklystron,
SLEDtiming

TD4V

The power supply failuers of CAMAC-based systemhave been occuered several times during the linac beam
operation. The replacement work of CAMAC crateinterrupts the beam operation for hour or more.
Futuermore, the CAMAC-based system is notcontrollable at the time interval of 20 ms, which is

Figure 2: Schematic drawing of event-based timing
system and timing signal distribution at the KEK linac.

required for the the simultaneous top-up operation. Fromthese resons, the many timing modules have been
replaced by a new event-based timing system. We havechosen the series-230 VME-based event system as thenew timing system [5, 6]. It has been originally developedfor Diamond light. Recently, the many accelerator
facilities have already adopted this system. An event
generator (EVG) and the event recievers (EVRs) havebeen installed at the main timing station and local timingstations, respectively. The EVRs can receive the timing
information through an optical fiber. EVRs can provide
the information as follws:


Sequence of programmed events in a pulse,
Regenerated clock signal,
Up to 14 delayed timing signals,
Shared data buffer up to 2 k bytes.

The clock signal of 114.24 MHz, which drive the firstsub-harmonic buncher of linac, is fed to the EVG asmaster clock. The EVG output can be transmitted to 20
EVRs through the fanout modules by the multi-mode orsingle-mode optical fibers. The CPUs and the operating
system of the VME computers are MVME5500 andVxWorks-5.5.1, respectively. The combination waschosen to satisfy the realtime performance required forthe simultaneous top-up operation. The EPICS driver
software is employed for the affinity of linac control
system. Since the installation of the EVG and EVRs
drastically reduced the number of used TD4/TD4V from172 to 17, the robustness and maintainability of thetiming system have been much improved.

TIMIMG WATCH DOG SYSTEM
Watchdog Module of 50 Hz Timing Signal
In the KEK linac, the modulators of high power
klystron should be triggered by the proper time interval of20 ms. when the trigger signal interval is longer or shorter
than 1 ms with respect to the fiducial timing interval of 20ms, the modulator turns off for the machine protection.
The noise signals could trigger the modulators in theshorter intervals. On the other hand, the longer intervals
could be caused by the misfire of the timing module.

Figure 3: GUI for 50 Hz timing watchdog module.

For the long-term stable operation, it is indispensable tomonitor the timing signal interval and signal loss
continuously. For this purpose, the watchdog module of50 Hz timing signal has been developed and utilized forthe linac operation. It is a NIM-based module of one
standard width with four LEMO connector ports, and theboth NIM and TTL level signals are acceptable inputs.
The module has a 100 Mbps Ethernet port by which thecontrol software can send the commands and receive thestatus information. All failure information of the 50 Hz
timing intervals have been accumulated into EPICS andCSS Archivers since the server software is developed as
an EPICS framework. When an abnormal timing interval
is detected, the linac operators can get immediately thefailure information by the GUI panel as shown in Fig. 3.
Fifteen watchdog modules in total have been installed at
the main timing station and six sub-control rooms. They
have been helpful for a quick finding of an abnormal
timing interval. Especially, it makes us easy to isolate theproblem between the timing modules and the others.

TDC for the Timing Jitter Monitor
Another useful tool is to monitor the accurate timing
interval. Figure 4 shows a timing signal chart example forthe high power klystron. The trigger signal sequence of 50
Hz is continuously delivered to the high power klystron
modulator. Each sequence consists of the timing for thehigh voltage, rf pulse, SLED timing, and so on. The
relative interval between each signal should be constantsince the variation of timing interval with respect toreference value affects the beam energy, which causes thedeterioration of beam orbit and emittance.
A time-to-digital converter (TDC) could be useful formonitoring the relative interval among the different
timing signals. We developed a new TDC module byusing Almazillo-9 (Atmark Techno, Inc.), which is a tiny
CPU module based on ARM processor [7], and TDC-GP1(acam-messelectronic gmbh) [8]. Table 2 summarizes themain specification of TDC module. This module has 10BNC ports as monitor inputs and one port as reference
signal input in which the NIM-level signal is acceptable.
The measurement time resolutions are 1 ns and 100 ns
with the duration of 3.27 ms and 200 ms, respectively. In
our case, the measurement mode of 1 ns resolution isinterested since the same timing sequence is repeated in
the time interval of 20 ms.
The module is running on Linux kernel 2.6.12. The
cross platform environment called ATDE, which is

Figure 4: Schematic drawing of timing signal structure forthe high power klystron.

Table 2: Specification of TDC module# of input

10Input signal

NIM

Measurement duration

3.27 ms (200 ms)

Measurement resolution

1 ns (100 ns)

CPU

ARM920T

CPU/bus clock

200 MHz/100 MHzInterface

Ethernet

SDRAM

64 MB

FLASH

8 MB

distributed by Atmark Techno, Inc., and VMware were
utilized for the software development. An EPICS device
support for the TDC module consists of the binary output
and waveform type records. The binary output record isused for the control of start and stop for the TDC
measurement. We use the waveform record as an array of50 measurements, each of which includes 14 parameters:the global counter value, timestamp, time interval datafrom
10channels,andmeasurement
status(normal/anomalous). The long-term data acquisition will
be tested soon after a slight modification is applied to thefirmware on Almazillo-9, and its result will be presented
elsewhere in the near future.

SUMMARY AND FUTURE PLAN
The timing system is one of most essential part for theKEK linac aiming at the complicated beam handling. The
new timing signal watchdog systems are developed andstably utilized for the KEK linac control system. Toward
SuperKEKB project, all timing signal will be monitoredby the new TDC modules developed here. It is expected
to support future SuperKEKB operation with more
complicated configurations.

REFERENCES[1] Mitsuo Akemoto et al., “The KEKB injector linac”,
Prog. Theor. Exp. Phys. (2013) 03A002.
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[3] http://cs-studio.sourceforge.net/docbook/.
[4] T. Suwada, K. Furukawa, N. Kamikubota, and M.
Satoh, “Trigger-timing signal distribution system for
the KEK electron/positron injector linac”, Nuclear
Inst. and Methods in Physics Research, A, Vol.521,
Issues 2-3, pp.549-555 (2004).
[5] K. Furukawa, M. Satoh, T. Suwada, T. Kudou, S.
Kusano, A. Kazakov, G. Lei, and G. Xu,“DEVELOPMENT OF TIMING AND CONTROLSYSTEMS FOR FAST BEAM SWITCH AT KEK 8
GeV LINAC”, in Proceedings of LINAC08, Victoria,BC, Canada, pp.404-406 (2008).
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