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

An injector of Super SORHiroshi Sakai*1 , Norio Nakamura1 , Hiroyuki Takaki1 , Tadashi Koseki2 ,Hiroyuki Hama3 , Tetsuo Shidara4 , Masanori Satoh4
1

Institute for Solid State Physics, Univ. of Tokyo (ISSP), Kashiwa, Chiba, 277-8581, JapanThe Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, 351-0198, Japan
3
Laboratory of Nuclear Science, Tohoku Univ., Mikamine, Sendai, 982-0826, Japan
4
High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan2Abstract
We present a design of the injector part for the SuperSOR ring of the University of Tokyo, which is a 3rd generation type vuv light source and is aimed to operate with
top-up operation scheme [1]. In order to realize top-up
operation, this injector consists of a pre-injector and asynchrotron. The pre-injector is a 200MeV linac and injects the electron beam into the synchrotron. In the synchrotron, the electron beam is accelerated from 200MeVup to 1.8GeV and its emittance and energy spread are reduced. In order to realize this low emittance beam, modified FODO lattice is applied. The details are presented inthis section.

consists of two main parts. One is the pre-injector which
generates the electron beam and acelerates its beam up to200 MeV and the other is the synchrotron whcih also accelerates the beam from 200MeV up to 1.8GeV Reeduced
beam emittance and energy spread enables us to inject
the electron beam to the main ring smoothly. Required
emittance and momentum spread are about 50 nm⋅rad and0.1%, respectively.
This paper is organized as follows. We will describe preinjector in the next section. In section 3, the synchrotron ispresented. Final section is devoted to the discussons andconclusions.

PRE-INJECTORINTRODUCTION
The Super SOR light source facility is a 3rd generation
vacuum ultra violet (vuv) and soft X-ray light source to beconstructed at Kashiwa campus of the University of Tokyo.
This facility aims to generate a high brilliant light stably.
In order to keep generating this high quality light, top-up
injection scheme is nesseccery for keeping electron beam
current of the main ring stably. The injector parts of the Super SOR are especially important to inject an electron beam
into the main ring without beam loss during thsi top-up operation. Fig.1 shows the plan view of this injector part. ItFigure 2: Layout of the pre-injector. The beam is accelerated in two different operation mode.

Figure 1: Plan view of the injector. All components are set
under ground and shielded by concreate blocks.
* e-mail address: hrsakai@issp.u-tokyo.ac.jp

Fig.2 shows a layout of the pre-injector. It consists ofa thermal gun, a sub harmonic buncher, a pre-buncher, abuncher and six accelerating structure units. Each accelerating structure is based on a SLAC type cavity and its
length is 2m. The bunching section and accelerating sections are driven by two 50MW klystrons and SLED cavity. There are two operating modes. Short and semi-longpulse modes are provided for injection to the storage ringin single and multi bunch operation modes of the ring, respectively. Both modes will be also utilized and optimized
for top-up injection. We describe both modes as follows.

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

EnergyRF frequency
Repetition rateBeam pulse mode
Pulse duration
Peak current
Normalized emittance
Energy spread

200 MeV
2.856GHz
50Hz
Short
Semi-long1ns(10ps) 100 ns (max)
0.8A
400mA
30 π mm⋅mrad
0.5% (FWHM)

Data
0.008
0.006
0.004
0.002
Energy spread (Full width)
0.01
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0

100

080

50

Table 1: Parameters of the pre-injector.

10060

150
200
Beam current [mA]

40
Total beam length [ns]

250
300

20350

In a short pulse mode, the electron beam is ejected as asingle bunch from a thermal gun with 1ns bunch length.
This beam is first compressed logitudinally (bunching) by
a sub-harmonic buncher, a pre-buncher and a buncher andits bunch length is reduced less than 10ps. Emittance ismaintained by adopting solenoid magnets. We calculate theemittance of the beam by PARMERA and it results in 30 πmm⋅mrad on the exit of buncher [2]. This beam is accelerated by accelerating sections up to 200MeV. In a semi-longmode, multi bunch electron beam with 100ns (max) pulse
duration is accelerated. Beam energy becomes more than
200MeV at the end of the accelerating section. However inthis mode, beam loading effect is dominant and total energy
spread reachs to more than 4%. This does not meet withthe aceptance of the synchrotron as described below. To reduce the total energy spread, we search the timing of phasereverse of SLED cavity corresponds to the beam injection
timing. Fig.3 shows the diffenence of energy gain with andwithout beam loading. Thanks to the beam loading effect,
100ns flat top is achieved. Fig.4 shows the result of thissearch with beam loading. Each transverse axis shows theinduced beam current and total beam length, vertical axis
shows the energy spread. Energy spread is reduced lessthan 1% on each condition. Beam current is tunable byutilizing by collimater which locates in front of a cathod ofgun. Parameters of pre-injector are summarized on Table.1.

400 0Figure 4: Results of injection timing search. Results oftotal energy spread are included beam loading effect.

SYNCHROTRONIn the synchrotron, the electron beam from the preinjector is accelerated up to 1.8GeV and beam emittanceis also reduced to meet with the injection condition of themain ring. In order to realize low emittance and small energy spread, larger circumference is better. Considering
given areas of Kashiwa campus, we desided that circumference of the synchrotron is about 93m that is one-third of
the main ring. Fig.5 shows the lattice design and Table.2
shows the parameters of synchrotron. Lattice is based on
FODO. There are 6 families of quadrupoles (QF,QD,QFX
on cell, QX,QY,QFM on straight section) and 2 familiesof sextupoles (SD, SF). In detail, one-cell consists of “QFSF-QD-SD-B-QFX-B-SD-QD-SF-QF” (Modified FODO)
as shown in Fig.5. Bending magnets are set on lower dispersion points, then we are able to reduce emittance lower.
Its emittance is smaller than that of usual FODO lattice ofsame circumference. However, dispersion of QF is muchbigger than others, then stronger magnetic field is requiredfor QF. At present 19T/m is required, which is enough torealize this magnetic field. RF frequency is same as themain ring. The repetition rate of the synchrotron is 1Hz.
Dynamic aperture of this lattice is calculated by using
SAD simulation code [3]. First we survey oprating pointon tune diagram and select horizontal tune ν x = 7.35 andvertical tune ν y = 3.30. After that, we recalculate the dynamic aperture on this oprating point. Fig.6 shows the results of dynamic aperture survey. Transverse acceperance
is larger than physical acceptance. Furthermore, energy accepetance is larger than ± 1%, which is enough for the electron beam from the pre-injector. Finally, ε x = 52.1 nm⋅ radis realized.

SUMMARY AND DISCUSSION
Figure 3: The energy gain on two condition (with beamloading and without beam loading)

We have described the calculated performance of the injector. The beam emittance is reduced to 52.1 nm⋅rad bythe synchrotron. Both pre-injector and synchrotron are designed to operate on a single and a multi bunch modes. It

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

80

∆ p/p = −1%∆ p/p = 0%
∆ p/p = 1%70

vertical aperture [mm]605040302010

QX
QY
QFM
QDQF
QFXQD
QF
QFX
QD
QF
QFX
QD
QF
QFM
QY
QX
QX
QY
QFM
QD
QF
QFX
QD
QF
QFX
QD
QF
QFX
QD
QF
QFM
QY
QX−40



−200

























−600−80

2040

6080

horizontal aperture [mm]

SFQFSD
QD

B

QFX

BQD
SDSF

QF

Figure 6: Results of dynamic aperture survey at 200MeV.
Horizontal axis is the dynamic aperture of hosizontal direction and vertical axis shows the dynamic aperture of vertical direction. Three lines shows the dynamic aperture oneach of three momentum deviation (∆ p/p = -1%,0%1%),respectively. Shadow area shows the physical aperture ofsynchrotron.

Figure 5: Lattice of the synchrotron. Top (Bottom) figure shows the lattice of all components (one cell). Squareroot of horizontal β function, square root of vetical β function and horizontal dispersion function are drawn at the top,
middle and bottom on each figure.

Parameters
EnergyCircumference
Lattice
Harmonic number
Horizontal emittance
Energy spread
Bunch length
Betatron tune (x/y)
Momentum compaction
Damping time (x)Damping time (y)Damping time (z)Bending field
Bending radius
Energy loss per turn
RF Voltage
RF frequency
Bucket height

Extract
1.8GeV

Inject0.2GeV
93.5m
Modified FODO
156
52.1 nm⋅rad 7.06 × 10 -4
13.7mm
7.35/3.30
0.01080.01085.73 ms
4.18 s5.80 ms
4.23 s2.92 ms
2.13 s
1.25T
0.139T
4.8m
193.47 keV
29.49 eV
500 kV
500.1 MHz
0.0070112
0.0307123

Table 2: Table shows the main parameters of the synchrotron.

is enough to inject the multi bunch beam to the main ringwith the top-up injection scheme.
Capture efficiency of the synchrotron is not enough on
a multi-bunch mode because of the followings. One is thedefferent RF frequency between the pre-injector and thesynchrotron. 2.856GHz is not devided by 500.1MHz, then
2.0ns spacing multi-bunch beam is not generated by theinjector complex. And the other reason depends on large
dispersion functions at QF. At present, energy acceptanceis determined by the physical aperture at QF due to thelarge dispersion when the beam is injected. This calculation including these conditons shows the capture effeciency
is around 45% [4]. In order to increase this capture effeciency and reduce the beam loss, some modifications areplanning. One is an enlargement of the bucket height in thesynchrotron to modelate the RF voltage, and the other isthe reduction of the dispersion funcition at QF by changing
the lattice slightly.

REFERENCES[1] A.Kakizaki, “A New Synchrotron Radiation Facility Projectof the University of Tokyo.”, The 8th International Conference of Synchrotron Radiation Instruments 2003 ,San Francisco, (2003).
[2] PARMERA is a sumilation code of gun design.
[3] SAD is a computer program for accelerator design. See“http://acc-physics.kek.jp/SAD/sad.html”.
[4] In a single bunch mode, the capture effi ciency is 100%.