The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

RF SYNCHRONIZED INJECTION FROM SPRING-8 LINAC TO
NEWSUBARU
Y. Shoji, S. Hisao, T. Matsubara, LASTI, Himeji Institute of Technology, 678-1205, Japan,
T. Asaka, S. Suzuki, and Y. Kawashima, SPring-8, 679-5198, Japan
Abstract
This paper confirms the occurrence of RF synchronizedinjection from SPring-8 linac to the NewSUBARU
storage ring. We use a new synchronization method
developed at SPring-8, wherein an instantaneoussynchronization between NewSUBARU RF (500 MHz)and linac RF (2856 MHz) enables a buckets-to-bucket
beam transfer. This is one of the key technologies of topup operations in a storage ring that uses a linac as aninjector. The RF clock and timing trigger signal are sent
to the linac from NewSUBARU, and this clock is used todelay units in order to maintain good synchronicity. Thisworks as a standard because it has a system tocompensate for transfer-time drift. The arbitrary
waveform generator is another key module. It produces aclock 1/32 of that of the linac RF using the NewSUBARURF clock. With this system, we realized more stable andefficient injection to NewSUBARU.

and NewSUBARU. The main parameters of the linac arelisted in Table 2. The stabilization and control of
longitudinal emittance has been one of the most important
R&D projects on the linac. In 2000, installation of Energy
Compression System (ECS) reduced the energy spreadfrom 1% to 0.5% (full width) and the energy fluctuationfrom 0.06% (rms) down to 0.01% (rms) [2]. In 2002, theRF synchronization between SY stabilized the beam
charge in one macro beam pulse [3].
streak camera(BL6)NewSUBARU

electron gun
chicane of ECS

1 INTRODUCTION(m)The synchrotron radiation facility NewSUBARU [1] isan EUV and Soft X-Ray light source at the SPring-8 site.
Laboratory of Advanced Science and Technology forIndustry (LASTI), at the Himeji Institute of Technology isin charge of its operation, collaborating with SPring-8.
The main parameters of NewSUBARU are listed in Table
1. The ring has two operation modes for users. In the 1.5
GeV mode, the beam is accelerated to 1.5 GeV and stored,
while in 1.0 GeV top-up mode, the beam current is kept at250+0.15 mA by an occasional injection with the gaps ofundulators closed.
The SPring-8 linac is an injector at the SPring-8
accelerator complex, supplying the 1.0 GeV electron
beam to the 8 GeV booster synchrotron (SY) andNewSUBARU. Fig.1 shows the layout of the linac, SY
Table 1: Main Parameters of NewSUBARU atthe injection energy.

0booster synchrotron

Figure 1: SPring-8 linac, booster synchrotron (SY) andNewSUBARU.
Here we report on the RF synchronization: between
NewSUBARU and the linac, which is more important
than that with SY because the injection efficiency is oneof the most important parameters of the top-up operation.
Lower efficiency means high radiation, which would
damage the permanent magnets of the undulators. The
injection efficiency of NewSUBARU is lower than 80%
when the undulator gaps are closed, although at thepresent this is acceptable because NewSUBARU has noin-vacuum undulator. The RF bucket of NewSUBARU at
Table 2: Main Parameters of SPring-8 linac withpulse width of 1 ns.

at 1GeV
500 MHz110 kV

Parameters
RF frequency
Operation rate

Synchrotron oscillation frequency

6 kHz

Peak current

Harmonic number

198

Macro Bunch length

1ns (40ns or 0.25ns is possible)

1 Hz

Micro Bunch length

10 ps (FWHM)

Natural emittance εxNatural Energy Spread

0.048 %Emittance εx / εyEnergy Spread

Natural Bunch length

40 ps (FWHM)

Energy Stability

30 nmrad.

40linacParameters
RF frequency
RF voltage

Maximum injection rate

20

without ECS
with ECS
2856 MHz
10Hz
2A

31 nmrad. / 58 nmrad.
1%

0.5 %

0.03 %

0.01 %

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

the injection point is shown in another report of thisproceedings [4]. Even if the bucket size is large enough,the injection efficiency is sensitive to the electron energy
from the linac. It is possible that the dynamic aperture of
an off-momentum electron is insufficient for an injected
beam, which has a large betatron oscillation amplitude.
The reduction of the energy spread and the time spread ofthe linac beam is expected to improve the efficiency.
However, simply a reduction of macro pulse width,
without the RF synchronization, is not good because it
increases the pulse-to-pulse fluctuation of beam charge.
The number of micro bunches (according to 2856 MHz)in a macro pulse (1 ns or less) is random. The RFsynchronization solved this problem.

or 40 ns but normally 1 ns is selected. The 1 ns macro
pulse contains two or three 2856 MHz micro bunches.

3 MEASUREMENTS
3.1Fluctuation of Beam Timing
We observed the micro bunch structure in a macro
pulse, which should be fixed under the RFsynchronization, using a streak camera (HamamatsuC6860) set up at BL6 of NewSUBARU [8]. The camera
was operated in double-sweep mode. A 1/6 of the mastertrigger was used as a fast-sweep trigger, and a trigger
signal for the injection pulse septum was used as a slowsweep trigger.
The camera observed a synchrotron light for 100ms
along the slow-sweep axis, which corresponds to about
250 revolutions and is equal to about a half ofsynchrotron oscillation period. The full range of the fastsweep axis was selected to be 2 ns, which is 360O in theRF phase of NewSUBARU. The 1 ns macro pulse wasinjected 20 times and the beam image was accumulated.
Three micro bunches synchrotron oscillated in one ofNewUBARU’s RF buckets, making three lines as shownin the middle image of Fig.3. When the AWG clock wasswitched to the internal clock, the macro pulse was still
synchronized to the RF bucket of NewSUBARU,
although the micro bunch structure became random. The
clear lines disappeared as shown in the bottom image ofFig.3.

2 SYNCHRONIZATION SYSTEM
Fig.2 shows a schematic diagram of the RFsynchronization timing system. One of keys of the system
is a stable distribution of the 500 MHz master signal. Thesignal is produced by a master oscillator at NewSUBARU
and distributed to the linac control room. A temperaturedependent phase shift of the optic fiber cable iscompensated by a PLL feedback, which uses a signal
returned along the same fiber [5]. The other key is asynchronus universal counter (SUC) [6], which counts the500 MHz signal with small jitters. By using SUCs as
digital delays and the 500 MHz master signal as a clock,the entire system synchronizes to one master signal. The
third key is a use of an arbitrary waveform generator(AWG), which produces a 89.25 MHz signal, 1/32 of thelinac RF frequncy. By using the 500 MHz master signal
as an AWG clock, the synchronization between themaster signal and the 89.25 MHz signal is established [7].
The signal is multiplied by 32 and is used as the linac'sRF signal.
The macro pulse width is determined by the pulse
width of the grid-cathode voltage of the electron gun. A
pre-trigger signal, which uses SUC to synchronize
NewSUBARU's target RF bucket, is produced atNewSUBARU and sent to the linac. The signal is resynchronized by SUC and is used to produce the highvoltage pulse. We can select pulse widths of 0.25 ns, 1 ns

3.2 Injection Efficiency
Injection efficiency into NewSUBARU was measured
for different injection phases of NewSUBARU RF. The
undulator's gaps were opened. Results of three different
cases are shown in Fig.4. With 1 ns macro pulse there wasalmost no tolerance of the phase for a 100% injection,even when the clocks were synchronized. However when
the transverse optics was well tuned, at the best phase we
obtained almost 100% injection in 10 out of 10 shots. We
can see a micro bunch structure as a step of the injection
efficiency, 1/2856 MHz = 63O apart.

synthesizer
2856MHzreference line
RFswitch

O/E

BPF
2856+1MHz

klystronpulse
modulator

Master signal(500MHz)
O/E
from
NewSUBARU

Klystron gallery

BPF
500+10MHz
clockclock
Pre-trigger
O/E
fr om
NewSUBARU

CFD

LU

digital delay(SUC)

phase shifter

reset waveformgenerato r(AWG510)

BPF
89.25+0.1MHz

3ch
rf selector

X32

E/O

2856MHz produced from
508MHz of SY rf

trigger mode
selectorclock
Permission of beam injection
from radiation safety

bunchingsection& dr iving
line

digital delay(SUC)Gun HV stationclock1Hzreset (SUC)

NIM->
+0.8V

E/O

O/E

CFD

NIM->
over 5V

pulser
-200V

gridcathodeassembly

0.25ns, 1ns, 40ns

Figure 2: Block diagram of RF synchronization system. The E/O and O/E blocks are electric-optic and optic-electric
converters. CFD and LU blocks are constant fraction discriminator and logic units. SUC is a synchronus universalcounter.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

04 DISCUSSION AND CONCLUSION

stored beamtime (ps)

500

1000

1500

2000
04000

8000

1.2 104count0

synchronized500time (ps)We experimentally confirmed the RF synchronizedinjection from the linac to the storage ring. There havealready been some data, which certify thesynchronization; however, the data in Fig.3 are the direct
proof. We found that an injection with a shorter macro
pulse will enlarge the tolerance of machine tuning at theinjection. Moreover, we proved that there is no serious
problem of the top-up operation using a linac as a direct
injector to the storage ring.
One problem of the system was that a shift of the RF
frequency of the storage ring changes the RF frequency ofthe linac and the beam energy. This problem was solved
by introducing an easy COD control system, which
stabilize the RF frequency of NewSUBARU against thehidden COD [9]. The RF synchronized injection during
the user time started in September 2003.

1000

1500

2000
01000 2000 3000 4000 5000

count
0random
500

time (ps)5 ACKNOWLEDGEMENTS

1000
The authors wish to thank Dr. N. Kumagai, a head of
the SPring-8 accelerator division, for his continuous
1500
encouragement. We also thank the staff of the 1GeV linac,booster synchrotron and the storage ring; especially Dr. Y.
2000
01000
2000
3000
Ohashi for his help to construct the timing system. We
count
thank Mr. H. Fukuda of MELCO for his help indeveloping the COD control system.
Figure 3: Electron bunch injected into NewSUBARU. The
bunch structure was observed by the streak camera set up
at BL6 in NewSUBARU. The images at center-right andREFERENCES
bottom-right are overlapped images of 20 injections. The[1] A. Ando, et al., J. Synchrotron Rad. 5, 342-344 (1998).
full scale of the vertical axis, the fast sweep, is 2000 ps.
[2] T. Asaka, et al., "Performance of the Energy Compression
Thefull scale of the horizontal axis, the slow sweep, is 100
System at the SPring-8 Linac", Proceedings of EPAC 2002,µs.
The
left-hand side plots are time structures at just after
Paris, France.
the injection.
[3] T. Asaka, et al., "Method for Stabilizing Beam Intensity andEnergy in the SPring-8 Linac", to be published in Nucl. Instr.
Meth. A.
[4] Y. Shoji et al, "Estimation of Non linear RF bucket of
NewSUBARU", this proceedings.
[5] Peschardt, and Salden, J. P. H., IEEE, 1989, pp.1960-1962.
[6] H. Suzuki, et al., Nucl. Instr. Meth. A431, 294-305 (1999).
[7] Y. Kawashima, et al., Phys. Rev. special topics -acceleratorsand beams, vol.4, 082001 (2001).

arbitrary Injection efficiency

10080

synchronized
0.25ns macropulse[8] Y. Shoji, et al., "Quasi-Isochronus Operation ofNewSUBARU", SRI’03, to be published as AIP Conference
Proceedings.
[9] Y. Shoji, "Hidden COD of NewSUBARU", this proceedings.

random
1ns macro pulse

synchronized
1ns macro pulse

6040200- 180 - 120- 60060
phase (deg)120180- 180 - 120 - 60060
Phase (deg)120180- 180 - 120- 60060
Phase (deg)120180Figure 4: Injection efficiency vs. injection phase of NewSUBARU RF. Points are measured injection efficiency. Lines
are averages of 10 shots. The phase of NewSUBARU's RF shifted, while the master signal, the macro pulse timing andthe micro pulse did not