TIMING SYSTEM UPGRADE FOR TOP-UP INJECTION AT KEK LINAC
K. Furukawa∗ , T. Suwada, M. Satoh, E. Kadokura, A. Kazakov
KEK, Tsukuba, Ibaraki, Japan
Abstract
KEK 8-GeV Linac provides electrons and positrons toPhoton Factory (PF) and B-Factory (KEKB). Because ofthe nature of those factory machines, both quantity andquality of the beams are required. In order to improve theinjections, quasi top-up injections of electrons to PF andKEKB rings have been planned and a new beam transportline was built. Fast beam switching mechanisms are beingdeveloped and installed. The timing and control system isalso reinforced to realize fast (50 Hz) switching of rf timing pulses, low-level rf, beam instrumentation parameters,
and beam feedback parameters. The present timing systemprovides precise (jitters down to 3 ps) timing pulses to 150
devices. Many of the signals will be upgraded to enable thefast switching scheme with an event system. At the sametime a double-fold synchronization between asynchronous
Linac and PF rf signals was developed to achieve precise
injection timing mainly because both rings have independent circumference correction systems.

laid and distributed over a coaxial cable. 15 stations receive
the overlaid signal and reproduce the timing and rf signals.
The system provide us a good timing stability of 3 pico seconds (RMS) even with variable delay synchronized to therf signal [2].
The event is sent with hard wires and with software messages over control networks. The fast event notifies information such as the pulse that has a beam or the beam withwhich instrumentations measure the quality. Only four gate
signals are transferred for this purpose, which was enoughfor the normal operation. The event gate signals are sent
over four twisted wire cables.
Slower event information is sent with the control system. Such information includes parameters of rf, optics,
timing and instrumentations, which add up to a thousand.
Presently the slow event or the beam mode switch typicallyoccurs every four minutes.

INTRODUCTION
The Linac routinely injects electron and positron beams
into KEKB-LER, KEKB-HER, PF and PF-AR rings withfour different characteristics. It takes 30 seconds to 2minutes to switch between beam modes, depending on
which magnets have to be standardized. The interruptionof physics experiments at a ring by the injection to anotherring is not small. The interruption is especially large whena beam development study is carried.
Thus, the fast switching of the injections between KEKB
and PF rings have been planned in order to enable quasisimultaneous injections, and the modified beam line is being constructed [1]. The timing and event system is also
upgraded to fulfill the fast switching requirement. The newsystem should provide the fast parameter switching, while
the timing precision should be kept to achieve the machinestabilities.

Figure 1: About 150 timing signals are provided through15 timing stations.

New System
TIMING/EVENT DISTRIBUTION
Among 150 devices which require timing signals, somerequires precise timing better than 5 pico seconds. At thesame time devices have to know the beam mode or theevent in order to operate with a corresponding parameters.

Present System
In the present system the timing and the event distributions are separated. A timing signal and rf signal are over∗ < kazuro.furukawa @ kek.jp >For the fast beam mode switch we have to change many
parameters synchronizing to an event. Thus, we decided
to employ the event timing system which was developed
for the Diamond light source [3, 4]. In the event systeman event generator send a stream of multiplexed signal andevent receivers regenerate the signals locally. And it greatly
simplifies the architecture as it distributes events, rf clock,
time stamps and data buffer over a single optical fiber.
As the maintenance of the present signal transmitter andreceivers requires careful tuning of the signal levels, the introduction of the event system is expected to be beneficial.

• Beam energy / orbit feedback systems
The present system needs about 30 seconds to 2 minutes
in order to switch between beam modes depending on themagnets to be standardized. Gradually it will be reduced
down to 20 milliseconds increasing the responsibility of theevent system.

TIMING RF SYNCHRONIZATIONThe stable operation of the beam is achieved by the goodsynchronization between rf signals of Linac and rings.

Linac-KEKB Synchronization
Figure 2: Event generator and receivers simplify the system, and they enable the fast switching of timing, digitaland analog signals.
Although we need more experiences for the timing precision and jitter of the system, it will be sufficient for themost of the signals. Only a few signals require a jitter of
3 ps, where we’ll keep the present system for a while.
At the beginning, 6 sub-timing stations are replaced with
event receivers, since those locations require fast switchingof analog and timing signals.

The injection system of the KEKB allows only 30-ps jitter of the injection beam against the ring rf. Thus, the master rf system was designed with an integer relation between4 rf signals [5]. Then a delay is added from common trigger
timing in order to select a bucket in the ring [6].

Figure 4: Four rf clocks are generated from a common master clock. The bucket selection system adds an appropriatedelay for the injection.
Figure 3: Six event receivers are installed at first, replacing
old timing receivers.

New Linac-PF Synchronization
PARAMETER SWITCHING
Digital, analog and timing values of equipment parameters are switched directly by an event or indirectly by software that is triggered by the event. Following parameters
are included.
• Pulsed bending magnet• High-power rf active / stand-by selections• Low-level rf parameters• Beam-position-monitor read-out modes• rf measurement parameters• Wire scanner modes
We need to operate on the machine that changes the property quickly. This means that several virtual machines need
to be manipulated at the same time. Thus, following functionalities should be provided.
• Parameter manipulation / display for each mode
• Mode dependent archiving

The rf clocks of Linac and PF-ring are independently designed and an asynchronously generated multi-bunch beam
is injected into an rf bucket of the ring. For the top-up
injection to PF-ring, however, requires higher stability ofthe beam quality and lower energy spread. The compatible
beam optics between KEKB and PF injections also requires
a further stability. To this end a single-bunch beam shouldbe accelerated even for PF-ring injection, and the jitter between the beam and the rf bucket is required to be less than
700 ps.
A new synchronization module was designed to satisfy
the jitter tolerance. While the design employs the same idea
as the system which was used in the previous project [7],the advance of the fast circuit enables the simpler design asin Fig. 5. This scheme provides the jitter down to 300 ps
and it is adjustable.
The injection tests have been carried several times. The
beam quality, the resultant injection efficiency and thebeam-loss radiation in the beam-transport line were all satisfactory.

is expected to simplify the timing and control system much.
The overall system will be tested in the next spring, and is
hoped to provide faster switching step by step.

REFERENCES
Figure 5: Double synchronization of rf clocks between
Linac and PF-ring.
The above synchronization technique depends on the accidental coincidence of the clocks. If two rf clocks have aninteger relation, no synchronous signal is achieved. Since
the both KEKB-ring and the PF-ring have circumference
correction systems by rf-frequency adjustment, such accidental synchronization has a risk. Actually, far integer relationship exists about 20-ppm away from the nominal frequencies.
Practically, the rate of the synchronous signal is determined by the jitters of related signals, and the both frequencies vary to the same direction under normal circumstances.
The synchronous signal is used to generate the 50-Hz pulse
for Linac, and the pulse timing homogeneity have to be better than 3 milliseconds in order to keep the stability of thehigh-power rf modulators. Thus, the frequencies are monitored so that they keep away from the integer relation.

BEAM PULSE SELECTION
After the fast beam mode switching is accomplished, theevent system will be programmed to provide a beam pulse
to one of PF and KEKB rings. Because power supplies ofseptums and kickers require that the pulse interval shouldbe constant at the moment, the beam pulse selection is restricted. Currently following three schemes are planned,
depending on how the rings request the beam. After thepower supplies are tuned, unrestricted beam pulse selection
will be enabled.

Figure 6: Three basic beam-pulse delivery schemes. This
is interim until the kicker/septum power supplies would beimproved.

SUMMARY
The new timing synchronization between Linac and PFring satisfies the injection timing criteria. This is important to make a stable injection into PF-ring. The fast beamswitching system is being installed employing a new timing/event system, which will cover many of timing andother parameters directly and indirectly. The event system[1] M. Satoh et al., “The KEK Linac Upgrade for the Fast Beam
Mode Switch”, these proceedings.
[2] K. Furukawa et al., “The Timing System of KEKB 8GeV Linac”, Proc. ICALEPCS2003, Gyeongju, Korea, 2003,
p. 130.
[3] T. Korhonen et al., “Timing System of the Swiss LightSource”, Proc. ICALEPCS2001, San Jose, USA., 2001,
p. 638.
[4] Y. Chernousko et al., “Diamond Timing System Developments”, Proc. ICALEPCS2003, Gyeongju, Korea, 2003,p. 244.
[5] H. Hanaki et al., “Low-Power rf Systems for the KEKB Injector Linac”, Proc. APAC’98, Tsukuba, Japan, 1998, p. 139.
[6] E. Kikutani et al., “The KEKB Bucket Selection System - Recent Progress and the Plan in the Near Future”,
Proc. APAC2001, Beijing, China, 2001, p. 669.
[7] T. Urano et al., Nucl. Instr. and Meth. A327, 1993, p. 529.