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

An injector of Super SOR
H i r o s h i S a k a i * 1, N o r i o N a k a m u r a 1, H i r o y u k i T a k a k i1，T a d a s h i K o s e k i 2 ,H i r o y u k i H a m a 3 , T e t s u o S h id a r a 4 , M a s a n o r i S a t o h 41Institute f o r S o lid State Physics, Univ. o f Tokyo (ISSP), K ashiw a ， C hiba ，2 77-8581，Japan
2The Institute o f P hysical a n d C hem ical R esearch (RIK EN), Wako, Saitam a ，351-0198, Japan
3L aboratory o f N u clea r Science，Tohoku Univ” M ikam ine, Sendai ，982-0826, Japan
4H ig h E nergy A ccelera to r R esearch O rganization (K E K ) ， Tsukuba ，Ibaraki ，305-0 801 ，JapanA b stra c t
We present a design of the injector part for the SuperSOR ring of the University of Tokyo, which is a 3rd gener­
ation type vuv light source and is aimed to operate withtop-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, modi­
fied 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. Requiredemittance 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.
P R E -IN J E C T O R

IN T R O D U C T IO N

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 Su­
per SOR are especially important to inject an electron beam
into the main ring without beam loss during thsi top-up op­
eration. Fig.l shows the plan view of this injector part. It

Beam Energy

Short (0. 8nC 50pps)
13MeV_ _ _I

Semi-long(400mA)
00 . 1MeV

1____
I_____

220MeV

13MeVI

GUN ：E le c tro n gun
PB：Prebuncher
ACC1-6 ：2 m a c c e le r a tin g stru c tu reI

SHB ：Sub-harmonic buncher
B：Buncher
SLED ：SLED c a v it y

Figure 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 accel­
erating structure is based on a SLAC type cavity and its
length is 2m. The bunching section and accelerating sec­
tions are driven by two 50MW klystrons and SLED cav­
ity. 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.

一590 —

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

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

200 MeV
2.856GHz
50Hz
Semi-longShortlns(10ps) 100 ns (max)
0.8A
400mA
30 7r mm.mrad
0.5% (FWHM)

Table 1:Parameters of the pre-injector.

In a short pulse mode, the electron beam is ejected as asingle bunch from a thermal gun with Ins 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 lOps. Emittance ismaintained by adopting solenoid magnets. We calculate theemittance of the beam by PARMERA and it results in 30 nmm.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.

2.30E+08
2.25E+08
c 2.20E+08•iH

60 2.15E+08

b0® 2.10E+08

ua

2.05E+08
2.00E+08
3.5E-06

3.6E-06

3.7E-06

3.8E-06t(s)3.9E-06

Figure 4: Results of injection timing search. Results of
total energy spread are included beam loading effect.
SYNCH RO TRO N

In 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 circum­
ference of the synchrotron is about 93m that is one-third of
the main ring. Fig.5 shows the lattice design and Table.2shows the parameters of synchrotron. Lattice is based onFODO. 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 vx = 7.35 andvertical tune vy = 3.30. After that, we recalculate the dy­
namic 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 士1%, which is enough for the elec­tron beam from the pre-injector. Finally, ex ニ 52.1 nm.rad
is realized.

4.0E-06

S U M M A R Y A N D D IS C U S S IO N

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-raa by
the synchrotron. Both pre-injector and synchrotron are de­signed to operate on a single and a multi bunch modes. It591 -The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

晏x^-xp(ul)E > x(horizontal aperture [mm].

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

«a> €() >>«.

E( ) XpFigure 5: Lattice of the synchrotron. Top (Bottom) fig­
ure shows the lattice of all components (one cell). Squareroot of horizontal(3 function, square root of vetical(3 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 radiusEnergy 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 x 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 ona 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 effe­
ciency 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 efficiency is 100%.