Timing System and Injection Control in the SRRC
K. T. Hsu, K. H. Hu, K. K. Lin, Jenny Chen, J. S. Chen, C. H. Kuo, C. J. Wang, G. J. Jan*Synchrotron Radiation Research CenterNo. 1 R&D Road VI, Hsinchu Science-Based Industrial Park, Hsinchu, Taiwan* Department of the Electrical Engineering and Institute of Electro-Optics
National Taiwan University, Taipei 107, Taiwan
Abstract
The accelerator system of SRRC has been operational
for nearly five years. There are good as well as badfeatures the present timing system. The timing systemupgrade project was started recently to improve its
performance and to satisfy new requirements. The SRRC
consists of three accelerators. The timing system provides
trigger signal to synchronize the injection sequence of a 50
MeV electron linear accelerator, 1.3 GeV booster
synchrotron and the 1.3-1.5 GeV storage ring. The timing
system also provides trigger signals for diagnostics deviceson the accelerator system. Trigger signal with picosecond
jitter is also available for streak camera trigger. Low phasenoise reference signal that phase locked with the RF clockis also provided for mode-locked laser systemsynchronization. The system will be used for thesynchrotron radiation-laser hybrid experiments in the near
future. Bunch synchrotron signal for time-resolved
experiments is also provided. Several injection control
applications are available for the machine operation.
Details of the timing system are described below.
1 Introduction
There are three accelerators at SRRC, one is a 50 MeV
linac, one 1.3 GeV synchrotron booster, and one 1.3-1.5
GeV storage ring. The booster and the storage ring use 500
Mhz Rf system. Harmonic number of booster is 120 andthe storage ring is 200. Timing system has been working
well during the last five years. However, some stringent
requirements still cannot be achieved before the upgrade ofthe system. The upgrade started in August 1997 and is
expected to finish on March 1998. Timing system update
work includes two parts. First, to find the source ofimperfection and to eliminate the problem. Second,improper timing system hardware and software will bereplaced by new design. Commercialy available timing
related module will be used for this upgrade.
2 Timing scheme of the SRRC accelerator complex
The major functional block of the timing system and thesignal distribution is shown in Figure 1 [1]. A
Rhode&Schwarz SMG signal generator is used as masteroscillator. The timing sequence for the klystron modulator,
the gun and the pulses magnets is shown in Figure 2. Clockgenerator produces revolution frequency of the accelerator
system and the 0.833 MHz synchronization signal which isthe coincident frequency of the storage ring and thebooster. Phase of the 0.833 Mhz system is used to control

the bucket position during injection.
Bucket addressing is done by shifting the phase of thesynchronization signal. A programmable delay generator
with a resolution of RF period exactly (2 ns), developed inhouse, is used for this purpose. The timing system of theinjector consists of a slow timing and fast timing system.
The slow timing system handles the phasing of thedipole/quadrupole power supplies and provides the trigger
signal for septums and bumpers. The fast timing systemgenerates the necessity signal for the klystron modulator,
the kickers and the gun trigger. Trigger signals for the
injection pulse magnets of the storage ring are also
provided by the slow and fast timing systems. Triggers ofinjection septum of the storage ring are derived from theslow timing system. Triggers for the storage ring injection
kickers are produces by the fast timing system. A multichannel digital delay generator is used to adjust the trigger
timing of the storage ring injection kicker.
3 Timing modules implementation
The timing system of SRRC uses three kinds of modulesof the existing system. One is the in-house development
module which is in C-size VME/VXI form-factor fordesign. The other is the timing module that was originate
from the vendor of the injector. The last category iscommercial digital delay generator. There are a lot ofsimilar designs at other facilities [2,3,4,5,6].
The in-house development timing module includes clock
generator unit (CGU) to generate the storage ring clock,booster clock, and synchronization clock. It also includes
Bucket addressing unit (BAU), injection control unit(ICU), clock distribution fanout ...etc. Old version isimplementd in Eurocard format. New revised modules
have been change into C-size VME/VXI format. The VME
crates are compliant with CERN spec. V431 which
provides necessary power for ECLinPS logic. LEMO
connector was used for the front panel signal connection.
VMEbus interface on timing module permit setting various
timing patterns by the control system. All trigger fanout
stages are implemented by monolithic 50 ohm pin-driver.
Figure 3 shows the CGU of new timing system.
The fast timing and slow timing delay module wereoriginal from the vendor of the injector. All modules are inEurocard format and installed on a customized crate. Fast
timing module are implemented by MECL logic andAD9500 analog delay generator. Slow timing logic wasimplement by TTL logic. Timing resolution of fast timing
system is 100 ps and the slow timing system is 100 ns. Thecontrol Bitbus interface is installed inside the crates.

The jitter introduced by the fast timing modules areslightly
large. The reason for large jitter is that slow rising edge
devices are used at input and output stages.
We also use commercial IEEE-488 based digital delay
generator (DDG) for various purposes. These DDG havebeen used for injection kicker trigger. The new system will
replace IEEE-488 based DDG by VME form-factor DDG.
VME timing module has fast control response, it ispromising for some special applications.
To improve system performance, the timing module andsignal distribution is now being revised. New system will
replace old MECL logic by ECLinPS logic and VME
DDG.

SR-Laser Synchronizer
reset

Beamline Instrumentation(20 MHz or 10 MHz)

Divider÷ 4, ÷ 8

to Mode Locker(74.946 MHz)

MasterOscillator
499.666 MHz(Rohde &Schwarz
SMG SignalGenerator)

VCXO
x 32

BeamLine

frev = 2.49833 MHZ
RF Distribution

STORAGERING

Storage Ring
RF System
SR User

Control system
Beam InstrumentationDivider ChainandBucket
Addressing(VME/VXImodules)

Booster to Storage Ring
Transport Line
Injection
SeptumInjection
KickerDigitalDelay
Generator

LINAC

Klystron Modulator,
Klystron Driver,
MWO

BOOSTERSYNCHROTRON

Injection Kicker

Sync. Signal
0.8333 MHz

Booster
RF system
andLinac
RF system,
Chopper,
BuncherFastTiming
SystemE-Gun Trigger
Extraction Kicker

4 Trigger and clock distribution

RF Ramp Trigger
Injection Septum
Extraction Septum
Extraction Bumper

SlowTiming
System

Dipole Field Zero Crossing

Harmonic number of the storage ring : 200
Harmonic number of the booster: 120
0.832776 MHz = 499.666 MHz / 600

Dipole, Quadrupole Power
Supply Phasing

Rev. 2.1
May 4, 1995
H. K. T.

Figure 1. Timing system block diagram
B(t)1.3 GeV @1915 A (Booster Dipole Current)

Major timing system modules are distribute in several
areas. The RF distribution is done by 1/2 inch phasestabilized coaxial cable (Andrew LDF4-50A). The trigger
connects to the high voltage desk for gun electronics via
fiber. The other signal is done by high quality coaxialcable. The RF reference sent to the injector system areinterferenced by the modulator noise. A high Q cavity filter
is used to reduce the effect of interference.

Dipole Field

5 Trigger for various subsystems

50 msect

Dipole Field Zero Crossing

Many systems and devices need trigger signals that arerelated to the timing system directly. Examples aredescribe below:
5.1 Trigger for diagnostics

Injection Septum
Klystron Modulator, Klystron Driver, MWO

There are many diagnostics devices that operate with thecycle of the injector at the booster-to-storage ring transportline and the storage ring. These devices include BPM,
charge monitor, radiation monitors and the turn-by-turn
BPM on the storage ring. The timing accuracy in nsec isenough.

Injection Kicker
Gun Trigger
Extraction Bumper(2 msec half sine)
Extraction Septum(500 µsec half sine)
Extracted Beam (Extraction Kicker - Booster)~ 232 nsec

Injected Beam (Injection window - Storage Ring)

5.2 Streak camera trigger

Injection Septum(300 µsec half sine)
Injection Kicker(1.6 µsec half sine)

Timing.chart
H. K. T.
Jan,. 5, 1992

Figure 2. Timing sequence of the injection process

A dual-sweep Hamamatsu C5680 streak camera has been
installed on the synchrotron radiation diagnostics ports tomeasure bunch length and to study longitudinal dynamics
in near future. The streak camera system needs low jitter
RF clock for operation. The RF clock is sent to the streak
camera through a high Q cavity bandpass filter and a DCblock. The injection 10n Hz are also provided forsynchronization. The jitter of the RF clock is less than 2
psec in rms.
5.3 Laser system synchronization

Figure 3. Clock generator unit

A mode-locked Ti-Sapphire laser system with repetitive
rate 79.946 Mhz was installed. The system will be used fortime resolved and two-color chemical dynamics
experiments. Pulse length of the laser system is adjustableform 2 psec to 60 psec. The harmonic number of thestorage ring is 200, repetitive frequency of the laser system
is chooses as 32nd harmonics of the revolution frequency.
The storage ring can be operated in 1, 2, 4, 8 bunches andkept fully synchronized with the laser pulse. A 79.946 Mhz
oven stabilized voltage control crystal oscillator (VCXO)
is used to generate 79.9642 Mhz and phase locked to ringclock. The tuning range of about +/- 800 Hz can satisfy theRF tuning range from 499.659 Mhz to 499.668 Mhz atcurrent user shift operation. The jitter can be controlled
within a few pico-second.
6 System performance
6.1 Single bunch operation
Single bunch electron beam is produced by a step
recovery diode (SRD) type pulser with about 1 ns in
FWHM. Single bunch impurity can be controlled to lessthan 0.001 compared with the main bunch easily after
proper setting of timing parameters, pulser amplitude andgun bias. The beam pulse is about 2 ns in length totally.
There is subharmonic buncher installed between gun andthe linac. Hence, the linac will produce about five to six 3
Ghz bunches. Only one or two of these bunches can be
captured by the booster. The allowed timing jitter of gun
trigger with respect to the ring RF is one linac rf cycle 330
ps for a single bunch operation. Revised timing system hasless than 100 psec (rms) jitter, more reduction is stillplanned.
6.2 Multibunch operation
Gun electronics operates in start and stop manner whenworking in multibunch mode. The timing system provides
a start signal and stop signal to gate the gun electronics.
Produced beam length is the difference of the time of bothpulse. The gun electronics can produce a beam with about
10 ns to 2 usec pulse length. However, since the revolution
period of the booster is 240 ns, beam length larger than 200
ns is useless. Length of the bunch train has about 10 ns
jittering in length, more improvement is necessary.

topping-up mode injection is also tested. All of these
operation modes reveal several shortcomings of the currentsystem.
8 Problems of the existing timing system
There are several issues of the current timing system andrelated injection problem. Problems that are caused bytiming jitter are one issue. Separate control for various
timing system settings causing the operationalinconvenience is another issue. Timing jitter is slightly
large. The jitter will degrade performance of many
applications and also increases difficulty of the machine
operation. Separate control system of the storage ring andinjector is not good from technical and operation point ofview. Injection process automation is not easy for currentsystem. Integration of the injector control system has beenlaunched recently. Timing system control related problem
can be solved in the near future.
9 Timing system improvement update
Efforts to reduce timing jitter is the highest priority. The
goal expected to achieve is less than 100 ps (rms) timing
jitter from ring RF to the beam pulse that are generated by
the gun. For minimum jitter, the trigger should have a highamplitude, high slew rate, and minimum noise. Note thatboth high-frequency noise (arcs, thrytron impulses, nearby
RF equipment) and low-frequency noise (unstablesource
amplitude, 60 Hz ground loops) can dither the trigger
threshold and induce jitter. Every crucial timing module aswell as signal distribution will be evaluated intensively tominimize added jitter.
The project of control integration of injector is under way.
Most of the timing system modules will be revised and will
use new implementation to achieve desire performance.
Improper timing distribution can possibly introduce jitteron the system. Improved timing signal distribution system
is also important for timing system upgrade.

6.3 Mixed mode operation
The machine can operate in mixed mode and fill a single
bunch in multibunch mode. Since TLS only 200 buckets,mixed mode operation cannot have many varieties. Special
timing is not needed for this operation mode. After routine
multibunch fill, we can fill one single bunch between thegap of multibunch.
7 Injection control and related applications
There are several control applications to aides theroutine operation. Current operation mode is mainly inmultibunch mode. Multibunch operation control interface
accepts input parameters including start bucket address andnumber of the step to fill, current per bucket, and bucket
advanced during injection. Current injection bucket
address is changed progressively, a trapezoid shape filling
pattern is obtainable. Single bunch injection has been used
for machine study up to now. However, We expect to havesingle bunch users in coming year. A simple application
supports random fill bunches of the storage ring for exotic
machine study. Mixed mode is also tested. Preliminary

10 Discussions and conclusions
The timing system update plan has been started recently
to improve its performance and to satisfy new
requirements. Problems of the existing system are undersystematic investigation. All imperfection will beaddressed in the new system. The new timing system not
only solve the timing problem of the accelerator system but
also will satisfy new requirement. The new timing system
will provide trigger signal for diagnostics devices, streak
camera trigger, and low phase noise reference signal formode-locked laser synchronization. Bunch synchrotron
signal for time-resolved experiments is also provided.
Several injection control applications are available for themachine operation. Injection related control applications
will be update also.
Acknowledgments
The authors express their thanks to the operation group
staffs, their skillful operation of the machine during testingis very helpful. The help of C. I. Hwang is also
appreciated.
[4]
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