The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Timing system of SPring-S
Hiromitsu SUZUKI, Yoshitaka KAWASHIMA, Norio TANI, Naoyasu HOSODA,Yuji OHASHI,Takashi OHSHIMA, Hiroyasu EGO,Masahiro HARA and Hiroto YONEHARA
SPring-8, Kamigori, Alm-gun, Hyougo, 678-12, JAPAN
Abstract
The timing system of SPring-8 has completed andmulti-bunch and single-bunch beam operations were tested
during the commissioning of SPring-8. In both the beam
operations, awed rf buckets of the storage ring could be
repeatedly filled with the beam from the synchrotron. The
multi-bunch beam with the bunch train of 1 JlS or 40 ns was
injected from the linac to the synchrotron, the single-bunch
beam was formed by the rf knockout system in thesynchrotron and the beam was injected into the storage ring.

1. Introduction
SPring-8 accelerator complex is composed of a linac, a
synchrotron and a storage ring. The synchrotron accelerates
an electron beam from 1 GeV to 8 GeV. The repetition rateis 1 Hz [I]. SPring-8 is operated in the multi-bunch and thesingle-bunch modes of an electron or a positron beam. Theelectron beam with the bunch train of 1 JlS and I ns from thelinac are used for the multi-bunch mode and the singlebunch mode, respectively. The positron beam with the bunchtrain of 40 ns and 1 ns are also used in the same way. As thebeam current of the positron is very low, in order to save theinjection time the beam is injected eight times from the Jinac
to the synchrotron in one repetition cycle. The radio
frequency of the linac is 2856 MHz, that of the synchrotron
and the storage ring is 508.58 MHz. There is no relation of
the phase of these two frequencies, which are supplied byindividual oscillators. To fill a beam in the same buckets ofthe storage ring repeatedly, an accurate timing system wasrequired especially in the beam injection of the single-bunchfrom the linac to the synchrotron. Therefore, the beam withthe bunch train of I ns from the linac must be filled in only
one bucket of the synchrotron with the time interval of about
2 ns. The accliracy of the timing signal which fires a gun ofthe linac is limited by the relation between the energy spreadof the beam and the phase difference between the if of theaimed bucketofthe synchrotron and the beam from the linac.
The time jitters must be less than 100 ps.
2. Timing system
To realize the accurate timing system, optic fibers,
electric to optic transmitters (EO) and optic to electric
receivers (OE) are used for the transmission line.
Furthermore, a 508.58 MHz non-stop-counter wasdeveloped for a master signal [2]. The radio frequency ofa
508 MHz and the master signal of 1 Hz are made in the Estation of the storage ring. The rf signal is divided andtransmitted to A,B,C and D-stations of the storage ring andthe control room for the injector. The master signal is also
used for the assignment of the buckets in the storage ring.
On the basis of these two signals, all of the triggers for thelinac and the synchrotron are made by the timing system of
the synchrotron [3].
2.1 Timing system of the storage ring

The timing system of the storage ring is placed at the Estation in the neighborhood of the A-station. There are asynthesized frequency generator of 508.58 MHz and a 508
MHz non-stop-counter which generates a master signal of 1
Hz. The counter has 30 bits and can put out a pulse at theinterval of2 s at most. The signal of 50&.58 MHz is divided
into the five stations. The master signal is transmitted to thecontrol ·room of the injector. The optic fibers and EO/OE
are used in the transmission line. Especially for thetransmission line of the rf signal, the phase fluctuations
between the E-station and the other one are monitored withthe mirror which reflects a part of received optic signal. If
necessary, a phase-lock-loop (PLL) can be driven to keep
the phase stable.

liN-out{revolutiea frequency)

508.58MIIz
To syachrotron

Fig. 1 Block diagram of the timing system at E-station.
Figure 1 shows the block diagram of the timing system atthe E-station. The master signal is exactly coincident withthe revolution frequency of the storage ring and thecommercial line frequency of 60 Hz. The harmonic numberof the storage ring is 2,436 and the revolution frequency isacquired by counting 2,436 of 508.58 MHz with a 508 MHz
non-stop-counter. There are two input and two output ports
in the counter. The input ports are connected with a 508MHz and a reset signal. The output ports are 1/N and M-out.

~so-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

1/N means that a pulse is put out every N counts of the 508
MHz and the N is 2,436 here. M-out means that a pulse isput out at the M-th of N. The beam can be filled in any
buckets by appointing the number of M. In order to makestable the excitation of all power supplies, the master signal
is synchronized with the commercial line frequency of thepower station. The master signal is acquired as the second
pulse of the revolution frequency after counting 61 of thecommercial frequency with two AND-circuits and two gategenerators. The first pulse is not used so that the mastersignal is not triggered by the commercial frequency which
has much time jitters.

of the transmission line. This could be repairOO immediately
by replacement of the module.

Wall current monitor

2-2. Timing system ofthe synchrotron

Fig. 2 The measurement system of the jitterswith the injector of the linac.

In the timing system of the synchrotron, all of the trigger
signals for the power supplies are made from rf signal of 508
MHz and the master signal of 1 Hz. About 100 triggers areused for a gun and modulators of the linac, power supplies
of bending, quadrupole, sextupole, correction and pulse
magnets, beam monitors and so on. The synchrotron is
operated by the timing signal. Especially in the single-bunchmode operation, the jitters for the gun trigger must be lessthan 100 ps and the jitters for the other one must be less thana few ns. All the timing signals are made by counting 508
MHz or the frequency of 508 MHz divided by 21,respectively. The delay times from the master signal to thetriggers are given by a preset value. All of the delay times
are decided with consideration of the distance from thetiming system to the power supply and from the power
supply to the machine, the electric delay in the circuit, therise time of the pulse and passing time of the beam at themachine from the gun.

3. Performance
The overall performance of the timing system for theSPring-8 is measured with a phase detector and a sampling
oscilloscope. The fluctuation of the rf phase between Estation and the synchrotron without the PLL is less than 1
degree of the 508 MHz. The distance between the twostations is about 700 meters. This measured value iscomparable to the performance of the phase detector. With
the PLL, the fluctuation can be decreased to less than 0.1
degree. The time jitters between the rf signal of 508.58 MHz
from E-station and the linac trigger of the timing system is 4
ps for one standard deviation (lo) and 22 ps for the overall
width. In 1994, the jitters between the linac trigger and thebeam current of the linac at the injector section wasmeasured withthe same timing system. Figure 2 shows themeasurement system with the injector of the linac. The jittersfor 1 cr was 7.4 ps. The total jitters for 1 cr was less than 10
ps and the overall width for 3 cr was estimated to be less than
60ps.
Once in a beam operation, the efficiency of the beam
injection from the synchrotron to the storage ring was
suddenly decreased because of the failure of a optic coupler

4. Beam operation
The beam commissioning of the linac, the syncrotron andthe storage rings were started in August, in December 1996
and in March 1997, respectively.
4-1. Multi-bunch operation

At first the beam commissioning of the synchrotron waspracticed in the multi-bunch mode operation of an electron
beam with the bunch train of 40 ns and .1 flS from the linac[4]. As the delay time of the timing system was adjusted
previously, the delay times except the gun and kicker
magnets did not need to be changed. The beamcommissioning of the storage ring was also started in themulti-bunch mode operation of a beam with the bunch trainof 1 f.lS. The stored beam current per pulse in the storage
ring was about 0.5 rnA. To store a beam current of 20 mAof which value was limited by the radiation security, 40
beam pulses were injected in the storage ring repeatedly.
When the beam current was decreased to less than 15 rnA,
the beam was injected again. The beam from thesynchrotron were ahnost put into the aimed buckets of thestorage ring, and it was exactly confrrmed by a single-bunchmode operation.
4-2. Single-bunch operation
In the storage ring a multi-bunch and a single-bunch·mode operations are required. However it takes a week toreplace the circuit of the gun grid-pulser for the multi-bunchmode operation by that for the single-bunch mode ope)'lltion.
The experiment which converts a multi-bunch beam fromthe linac into a single-bunch beam with an rf knockout
system installed in the synchrotron, was tested.
The beam is kicked out in the vertical direction by the rf
knock-out system at the injection energy of l GeV. Because
the vertical aperture is smaller than the horizontal one andthe damping time of 0.87 s at l GeV is estima.fed to belonger than that of 2 ms at 8 GeV and the required rfknockout power at 1 GeV is smaller than that at 8 GeV. The-81-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

phase difference of the rf current on the four electrodes forthe rf-knockout must be 180 degree alternately as shown infigure 3. The maximum rfpower is 50 watt per electrode. At
the resonance point of the betatron tune the beam is kickedout in the vertical direction, and the beam is lost within
about 30 ms after the beam injection. The condition of theresonance is expressed in equation (1).
fknockout= [n±{vy-lnt(vy)}] X f..evolution
n : 0 or positive integer

AmpHtude

V oln(2pl-<,1376)t • rectaagle(2pi.J'...IU)tI

I~~I(I)

where the f..evowrion is 756.8 kHz. The Vy is a vertical tune.
The Int(vy) means a integer of Vy· The vertical tune value
were selected to 8.7833. Figure 3 shows the block diagramof the rf knock-out system for the formation of the singlebunch mode. The beam bunch train of 1 J.l.S or 40 ns for themulti-bunch mode operation is injected into the synchrotron,
most of the beams are kicked out at the vertkal betatronresonance with the rf knock-out and only one bunched beamis remained. Most of the beams are kicked out at the verticalbetatron resonance with the rf knock-out. The signal of theknock-out is made by composition of a sine wave resonatingwith vertical betatron oscillation and three rectangle pulse of
frtl12, fn/21 and frtl32. Equation (2) is the knockout signal
for the single-bunch mode operation.
V knockout= Vosin(27tfrtl3 76)tX rectangle(27tfrtlm)tm: 12, 21,32

Fig.4. The signal for the rfknockout.
"T1al<--

bucket number

1610"""""""'1219

1828

1Fig.5. The wave-form of four equally-spaced bunches in thestorage ring with the aimed bucket changing four times.
5. Conclusion(2)

The fre is the radio frequency of 508.58 MHz. The fre./376
means the knockout frequency of 1.3526 MHz. It
corresponds to n=l in the equation (1). The least common
multiple of 12,21 and 32 is equal to the harmonic number of672. There are only two points of a revolution cycle at which
the beam is not kicked out commonly by three kinds ofrectangle pulses. If the beam is not injected at the one point
but at the other point, only one bunched beam remains. The
three kinds of rectangle pulses are switched at the interval of
40 ms one after another in the flat bottom of 150 ms [5][6].
Figure 4 shows the signal for the rf knock-out. Figure 5
shows the wave-form of four equally-spaced bunches in thestorage ring with the aimed bucket changing four times. Theinterval ofbunchs is 609 buckets.

The timing system of SPring-8 is successfully completed.
The performance is confirmed with the multi-bunch and thesingle-bunch beam operations. The commissioning of theSPring-8 was succeeded smoothly with the timing system.
The beam is supplied steadily to the storage ring. The firstbeam-line experiments will be started in October 1997.
The beam test to inject eight equally-spaced single bunch
beams into the synchrotron is planned in September 1997.
The impurity of the single bunch in the storage ring, which
is defined as the ratio of the neighborhood-bunch beam tothe aimed-bunch beam will be measured with the photon
counting method from September. There is not yet an rfknockout system and any equipment to prevent the increaseof the impurity of the single-bunch beam in the storage ring.
To make the purity better, the knockout system should beinstalled as soon as possible.
References,.

Fig.3. The block diagram of the rfknock-out system
for the formation of the single-bunch mode

[1] H. Suzuki et al. Rev. Sci. Instrum. 66 (2) (1995)
1964-1967.
[2] H. Suzuki et al. 9th Symp. on Ace. Sci. Tech. (1993)
249-251.
[3] H. Suzuki et al. lOth Symp. on Ace. Sci. Tech. (1995)
252-254.
[4] H. Suzuki et al. J. Synch. Rad. (1997) To be published.
[5] K. Fukami et al. lOth Symp. on Ace. Sci. Tech. (1995)
109-111.
[6] H. Yonehara et al. Rev. Sci. lnstrum. 66 (9) (1996).

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