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

Status of the VSX Project
A VUV and Soft X-ray High Brilliance Synchrotron Radiation Source
VSX accelerator group, presented by Norio NAKAMURA
Synchrotron Radiation Laboratory, Institute for Solid State Physics (ISSP)The University of Tokyo, Midori-cho 3-2-1, Tanashi, Tokyo 188, JapanAbstract
The VSX project aims at constructing a VUV and soft
X-ray high-brilliance synchrotron radiation source in a new
campus of the University of. Tokyo (Kashiwa Campus).
The VSX light source is being designed intensively at theInstitute for Solid State Physics (ISSP). The 2 GeV storage
ring has a low emittance optics (Exo- 5 nm·rad) with wide
dynamic apertures and 16 straight sections mainly used byinsertion devices, which can produce VUV to soft X-ray
radiation with a maximum brilliance of about 1020
photons/(sec·mm2·mrad2 ·0.1%b.w.). The linac and booster
synchrotron meet the full energy injection of both positronand electron beams to the storage ring. The R&D's on thedamped RF cavity and the single-pass monitor areprogressing well. Prototypes of bending, quadrupole andsextupole magnets are now being manufactured and tested.

1 Introduction
The VSX light source [1] is a third-generation VUV· and soft X-ray synchrotron radiation source and its hi-ghly
brilliant radiation will be used for nationwide user groups ofsolid state physics,• surface science, atomic and molecularscience, chemistry, life science, micromachining and so on.
The proposed VSX site is in a new campus of the university
called Kashiwa Campus, to which several existing facilitiesof the university including ISSP will move in near future.
The VSX light source will be constructed and managed by a
newly organized body. directly belonging to the university,
the Center of High-Brilliance Light Source, which issupposed to join with a few other facilities for acceleratorrelated science into the Center of Accelerator Science after
the construction of the light source. The conceptual design
report for the VSX accelerators was already published inMay 1996. Further study on the accelerator design is goingon. In 1997, the government decided to give a budget for
preparatory work for the VSX project. Based on thisbudget, a new R&D on storage ring magnets have been
started in addition to those on the RF cavity and the singlepass monitor. This paper reports on the present status ofthe project.
2 Accelerator
Figure 1 shows a layout of the VSX accelerators withthe experimental hall in the light source building. The
accelerator complex consists of a linac, booster synchrotron
and storage ring. The linac and synchrotron lie under theground, while the storage ring is on the ground.

Fig. 1 Layout of the VSX accelerators.
2.1 Storage Ring

The 2 GeV storage ring has a lattice type of DBA with
16 cells and 4 superperiods. The fundamental parameters ofthe storage ring are summarized in Table 1. In the latest
design [2], we obtained wide horizontal and vertical dynamic
apertures for an emittance of 5.1 nm·rad by optimizing theharmonic sextupoles. The horizontal and vertical dynamic
apertures are -150crx and -120cry (crx, cry: horizontal arxl
vertical beam sizes) for zero momentum deviation, arxl-lOOcrx and -90cry even when realistic field and alignment
errors of magnets are taken into consideration.
The storage ring has four 14.3 m long str~ght
sections and twelve 7 m semi-long straight sections. The 7m semi-long straight sections are used for 10 insertion
devices, injection magnets and RF cavities. Each of 14.3 m
long straight sections is aimed to install a long undulator
with a length of about 12 m, or a few kinds of undulators
which may produce synchrotron light with different
polarities and/or wavelengths. Figure 2 shows the spectralbrilliances of 12 m undulators with typical magnetic periods
and the bending magnet. The maximum brilliance of the-510-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997YSX light source can exceed 1020 photons/(sec·mm2 ·mrad2·0.1%b.w). The photon energy is available up to a few keY
by use of the higher harmonics. Multipole wigglers arealso installed for generating hard X-rays above 10 keY.
Table 1: Fundamental parameters of the storage ring
EnergyLattice type
Superperiod
Circumference
Semi-long straight section
Long straight section
Natural emittance
Energy spread
Momentum compaction
Horizontal tune
Vertical tune
Horizontal natural chromaticity
Vertical natural chromaticity
Horizontal damping time
Vertical damping time
Longitudinal damping time
Revolution frequency
RFvoltage
RF frequency
Harmonic number
Synchrotron tune
Bunch lengthRF-bucket height~,.Q....~-e~""c::'

E [GeV]N,C [m]E,0[nm•rad]

crlE

av,
vv

s,

Sv
't, [msec]'tv [msec]'tz [msec]
freJMHz]VRF [MV]fRF [MHz]hv,
crz [mm](AEIE)se2.0
DBA4
388.457.0mx 1214.3m x 4
5.10
6.66xlo-".
6.87xJ0-4
18.84
9.55
-47.78-18.45
24.17
24.25
12.14
0.771759
1.4
500.1
648
0.007
4.04
0.028

Table 2: Fundamental parameters of the linac
Totallength[m]Repetition rate[Hz]Beam mode
Energy[MeV]
Pulse duration
Peak current[A]Energy spread[%]

1 o"

InJeCtiOn energy
Maximum energy
Circumference
Maximum repetition rate
Natural emittance (2 GeV)
Energy spread (2 GeV)
Momentum compaction
Horizontal tune
Vertical tune
Revolution frequency
Harmonic number
Synchrotron tune
Bunch lengthRF-bucket height174>

10 15~"' 10=:3·c
ll:lelectron
semi-long300
0.3 j.lS
50±0.25

short
310
Ins
200±0.25

long
230
4 j.lS
300-short250
1 ns10±0.25

positronsemi-long250
15-30 ns6±0.25

Table 3: Fundamental parameters of the synchrotron1 o'""c' 1 o'"....=c.c:g.

68.23
50 (max.)

1 020.E 1 o'""'ee 10""''--more than 250 MeY and the momentum spread less than
0.25 % (with an Energy Compression System on) for alinac length of about 70 m. In the long electron beam mode,the high-power electron beam is provided for a slowpositron production target in the slow-positron experiment
facility. The linac can be dedicated to slow-positronexperiments when the storage ring is in a storage mode.
The booster synchrotron accelerates the electron orpositron beam from the linac up to 2 GeY for the fullenergy injection to the storage ring. The lattice is a FODO
type with a betatron phase advance per cell of 95 degrees andtwo dispersionless straight sections for an RF cavity and aninjection/extraction system. The fundamental parameters arelisted in Table 3. By use of this synchrotron, the design
beam current of the storage ring, 400 rnA for the multibunch operation and 10 rnA for the single-bunch operation,can be stored within a few minutes for the electron beam andwithin thirty minutes for the positron beam.

1410131 o'

1 o'103

E;n; [GeV]
Emax [GeV]C [m]f,.n[Hz]E,0 [nm•rad]
crlE

av,vv
f,.y[MHz]hv,
crz[mm](AEIE)

0.25-0.30
2.0
97.11
4304
7.59x10-4
0.058
5.17
4.79
3.087
162
0.024
260.004~1 o'Photon Energy[eV] ~Fig. 2 Brilliances of 12m undulators with typical periods
and the bending magnet.

2. 2 Linac and Synchrotron
The linac can generate and accelerate a positron beam
as well as an electron beam with a maximum repetition rateof 50 Hz. The linac parameters are shown in Table 2. Thislinac has five beam modes; the pulse length and peak currentof the linac beam depend on these beam modes. In four
beam modes, the linac feeds the electron or positron beam tothe synchrotron. The short and semi-long beam modes
correspond to single-bunch and multi-bunch operations of
the storage ring, respectively. Two SLED cavities areadopted for the positron beam to obtain the beam energy

3R&D

3.1 Damped RF Cavity

We have developed a single-cell 500 MHz cavity witha simple damped-structure. The cavity has a beam duct witha comparatively large diameter on each side and a part of thebeam duct is made of an SiC microwave absorber. The
higher-order modes (HOMs) are guided out of the cavity to
the beam ducts and dissipated by the SiC part. It wasalready confirmed in the low-power test of two cold-model
cavities that Q-values of the HOMs are strongly damped by
the SiC absorber [3]. Furthermore a high-power model ofthe cavity was manufactured, and after the high-power
conditioning for 60 hours input power of 150 kW was
attained without any severe problems. It means that the-511-

The II th Symposium on Accelerator Science and Technology, Harirna Science Garden City, 1997

cavity can store RF power five times as high as the required
one [4].
In the summer of 1996, two damped RF cavities wereinstalled at the Photon Factory (PF) storage ring in place of
two old cavities(Fig. 3). The new cavities were successfullyoperated for the scheduled two-month user run in the autumnof 1996. During this operation, any dangerous coupledbunch instabilities were not observed. In addition, themaximum stored current of 773 rnA, a new record higher by-200 rnA than the last one, was achieved [5].

Prototypes of all three magnets are currently fabricatedand tested at Energy & Industrial Systems Center of
Mitsubishi Electric Corporation. Figures 4 and 5 show thebending and the quadrupole magnet prototypes, respectively.
The bending and quadrupole magnet prototypes will bedelivered in September 1997 and their field measurement
will be carried out this autumn. The construction of thesextupole magnet prototype is also in progress, and it will
be completed by the end of December 1997.

Fig. 3 Damped RF cavities installed at the PF ring.

Fig. 4 Prototype of bending magnet under test.

3.2 Single-Pass Monitor

Single-pass measurement of beam position is expected
to play an important role in commissioning and tuning ofthe VSX accelerators. A program to develop a single-passmonitor system using a fast digitizing oscilloscope is under
way at a 500 MeV electron storage ring, SOR-RING[6]. In
this system, the four button signals of four beam position
monitors (BPMs) are combined by the RF power combiners
and then fed into a 4-chaimel digital oscilloscope (TDS684Aby Tektronix). Each channel of the oscilloscope has a 8-bit
digitizer with a maximum sampling rate of 5G samples/sand a maximum record length of 15000 points.
Thedigitized data are sent to a workstation (HP715), and thebeam position is calculated from the intensities of four
button signals. The relative accuracy of less than 100 )lm
has been obtained in this system.

Fig. 5 Prototype of quadrupole magnet under construction.

References

3.3 Magnet

The VSX storage ring contains 32 identical bending
magnets with 1.3 m long, 144 quadrupole magnets withtwo different lengths, 0.4 m and 0.6 m, and 128 sextupole
magnets with 0.15 m and 0.2 m. All these magnets areconventional, room temperature, DC magnets, and they are
optimized for a nominal operating energy of 2.0 GeV, butcapable of reaching a maximum energy of 2.5 Ge V. The 2dimensional field calculation of the magnets was made by
the computer program LINDA, which allowed to determinea pole shape with shim profile.

[1] Y. Kamiya et. al, Proceedings of the 4th European

Particle Accelerator Conference, London, 1994, p639.
[2] H. Takaki, et al., Proceedings of the 1997 Particle
Accelerator Conference, Vancouver, 1997.
[3] T. Koseki, et al., Rev. Sci. Instrum., 66 (1995) 1926.
[4] T. Koseki, et al., Proceedings of the 5th European
Particle Accelerator Conference, Barcelona, 1996,p.l988.
[5] M. Izawa, et al., Proceedings of the 1997 Particle
Accelerator Conference, Vancouver, 1997.
[6] H. Kudo, et al., Proceedings of the 1997 Particle
Accelerator Conference, Vancouver, 1997.

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