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

Performance of the SPring-S Storage Ring Vacuum System
Haruo OHKUMA, Kowashi WA'D\NABE, Hiroshi SAEKI, Mitsuhiro MASAKI,Yasuaki SUZUKI, Yukiko 'D\NIUCHI, Takashi NODA, and Michio MAENO
Accelerator Division, SPring-8, Kamigori, Ako-gun, Hyogo 678-12, Japan
Abstract
The installation of the vacuum system of the SPring-8
storage ring was completed during 1996, as was the vacuum
control system. Most of the vacuum chambers are mare ofaluminum alloy. The main pumping system is a mixed one
consisting of NEG strips, DIP, SIP, and LNP. In addition tothe standard treatments for ultrahigh vacuum components,
dust-controlled procedure was adJpted in the manufacturing
and the installation processes. In the commissioning phase,the photon induced desorption phenomenon was observed
The operation of the vacuum system shows good features ofquick beam self-cleaning. The perfonnance of the overall
vacuum system is to be described

1. Introduction
The SPring-8 with a beam energy of 8 GeV and a criticalphoton energy of 28.9 keY has been undergoingcommissioning since March 1997. It will be open to the users
with ten beamlines since October 1997.
In the synchrotron light source, due to the large desorption
induced by the synchrotron radiation (SR), The dynamic
pressure in the electron storage ring vacuum system is very
high in the early stage of commissioning, in spite of the factthat a static ultrahigh vacuum environment has been achieved

The interactions between the electron beam and the gas
molecules desorbed from the chamber surface result in beamloss and emittance growth. Many criteria must be consid!red
when designing the vacuum system of an electron storage ring.
The design, fabrication, and testing of the vacuum chambers
have been described before [1]-[4].
In this paper, the construction and the commissioning of
the SPring-8 vacuum system are described.
2. Vacuum system
The manufacture and installation of the vacuum system of
the SPring-8 storage ring was completed in October 1996.
The vacuum control system including an interlock system forthe purpose of vacuum safety, which was built in order toincrease the reliability of the vacuum operation, was also
completed at the end of 1996.
A layout of a nonnal unit cell is shown in Fig. 1. Thevacuum chambers of normal unit cell consists of three straightsection chambers (SSC's) with an absorber, two bending
magnet chambers (BMC's), two crotch chambers (CR's)
equipped with an absorber-crotch, two rf-shielded gate valves,
one dummy chamber (IDD), four bellows assembled chambers(BEC's). A dummy chamber will be replaced by the vacuum
system of the insertion device one by one.
The vacuum chamber materials are mainly aluminum

(a)-1

RGV2
I

(a)-2BESCSIPSIPSIP' ~-Fig. 1. A layout of the normal unit cell. (a)-1 and (a)-2 are top and side views of the downstream
section of the cell, respectively. (b) is the side view of the upstream section of the cell.

-359-(b)The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997
Colling Water

NEG Chamber

Fig. 2. The cross section of the bending magnet
chamber (BMC).
alloys to benefit from their low outgassing rate, high thermal
conductivity, low radio activity, and so on. The sse and theBMC are mare of A6063-T5 aluminum alloy by extrusion
with the cooling channels on the both sides. The sse consistsof a beam chamber and a slot-isolated antechamber in which apair of non-evaporable getter (NEG) strips, allowing for
distributed pumping are installed The BMC inclures a
rectangular pump channel in which a distributed ion pump(DIP) is installed, abeam chamber and a slot-isolated
antechamber in which a NEG strip is contained The beamchambers of the sse and BMC are extru<hl with the samecross section in an ellipse 70 mm in width and 40 mm inheight. Figure 2 shows the cross section of the BMC.
To achieve a beam lifetime of approximately 24 hours, thevacuum chamber with its pumping system should be designed
so as to maintain the beam-on pressure of the order of 10-7 Pa
or less with a circulating beam of 100mA. In our vacuum
system, synchrotron radiation is almost intercepted by thecrotches and absorbers placed just downstream and upstream ofbending magnets. An only photon emission for energies lessthan 10 eV with a angular spread larger than 1.5 mrad in thevertical plane is intercepted by a slightly part of 10 mm
photon beam slot walls of chambers.
The main pumping system is based on NEG strips which
are used in the SSC's and BMC's to evacuate the scatteredmolecules, and lumped NEG pump (LNP) for evacuating
mainly SR-induced gases at the crotch and absorber location.

In ad:lition to the NEG strip, a DIP is installed in along-side
the beam chamber of the BMC. A sputter ion pump (SIP)
which assists the LNP is also used The vacuum system isdivi<hl into 48 unit cell by rf-shiel<hl gate valves and was
installed and evacuated section by section. During chamberbaking and NEG activation, we use the movable-type roughpumping system which consists of a rotary pump (RP) with afore-line trap and a turbomolecular pump (TMP). The RP's areused to evacuate the vacuum system from atmosphere. TheTMP's are turned on when the pressure reached the 1 Pa region.
All of the SSC's, BMC's and IDD's were 150 °C prebakedin
advance of the chamber installation in the storage ring tunnel
in order to remove chamber warps which were caused by theconstruction process and welding. The NEG pumps wereactivated at the last stage of pre-baking procedure. Residualpressure after the pre-baking was the order of 10 -s Pa orless.
All of the installation works were accomplished in a clean
room or clean booth. After the installation of the vacuum
system in the storage ring tunnel, the 140 °C baking of thevacuum system and the NEG activation were done once again,section by section.
The photon absorbers are mare from Glid-Cop (AI andAl 20 3 dispersion strengthened copper) because of highallowable thermal stress of 60 kg/mm 2, compared to 10kg/mm2 of OFHC. The absorbers have the structure in which
particles ·such as reflected photons, photo-electron and SRindiced outgases are efficiently trapped SR-induced outgases
are evacuated locally by the high capacity pumping systembefore the outgases have a chance to bounce into the beamchamber. The part of the photon beam power from a bending
magnetof10.5 kW, about6.6 kW(34kW/cm2) is irradiatedat
the photon absorber of the crotch .and the remaining beam
power deposited at the absorbers placed oownstream of thecrotch.
CE-12 Al···.----------------------,
1 ••.....

H 2 ...

......

1.2........ co......

Beam-on pressure at #11 cell••• J.,...\..L~~......,..,~~~.........~:!:"'""'~:c"""'"""'""":'C"'"""""...-..,::'""'"""'"'"T~..-r
"

~H~

H

"

~~"

Fig. 4. Quadupole mass spectrum for a beamourrent 1.1 rnA at accuinulated oose of
10.9Ah.

3. Commissioni ng
The averaged pressure readings of the storage ring are~1x10-a Pa without electron beam, 5xl0·7 Pa at a beam

Beam Dose [A•h]Fig. 3. The pressure per Ampere of the electron
beam current versus the accumulated beamdose at several points in the unit cell.

current of 18 rnA. After a continuous cleaning by the SR, thepressure riseto the photon induced desorption (PID) effectwas significantly reduced. Figure 3 shows the curves of thepressure per Ampere of the electron-beam current (P/f) at
various position of unit cell versus the accumulated beam dose.
The value of PII decreased by about two orders of magnitudedue-360-The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997after an accumulated beam dose of 11Ah. It shows the beam
self-cleaning effect on the vacuum chamber.
A massspectrum at beam current of 1.1 mA and a dose of 10.9 Ah isshown in Fig.4. The dominantdesorbed gases areH2 and CO.

t"';;l'E~·C[ho~r]l_ _]1 0 ----·

5I

20~';:
0c::"1

relationship can be described by the following formula:(J ]0.65

1-r -110

I dtmAh.

The trend of the It curve is retermined by scattering of theelectron beam by the photo-<borbed gas resirent in the ring.
vacuum system.
In the summer shut-down period, all of the NEG strips am
LNP were re~activated. The beam-on pressure was redl.K;ed byabout one second, and then the beam lifetime increased
About 70 hours beam lifetime was achieved at 18 rnA of thebeam current..

~s -Ll.-+-·-··-···········-L-- --1-·--···

References

100 '---'---'-~--'--~-'---'--L~__JL_-'---' 0101220468

Time [hours]
Fig. 5. The beam current and the lifetime of thetypical operation.
An accumulated dose of 11Ah and a lifetime of 35 hours at19 rnA current were achieved after four months' operation.
Figure 5 shows the electron beam current and beam lifetime on
the typical operation. The gap of the insertion device has beenclosed cbwn to 8 mm of the minimum gap of the standard
in-vacuum type undulator of the SPring-8, the beam lifetime
is reduced due to narrow gap of the insertion device.

~.

[1] H. Ohkuma et al., "Vacuum System for the SPring-8
Storage Ring", Proc. of the 9th Meeting on Ultra High
Vacuum Techniques for Accelerators and Storage Rings.
KEK, March 3-4, 1994, KEK Proceedings 94-3, 29.
[2] K. Watanabe et al., ''R&D of A Full-size Cell for theSPring-8 Storage Ring Vacuum System", Proc. of theInternational Conference on Vacuum Science &Technology, India, 1995, 58.
[3] S. Yokouchi et al., ''Vacuum Performance ofPumping
System for Crotch and Absorber of SPring-8 StorageRing", ibid., 197.
[4] S Talcahashi et al., ''Manufacture of the Crotch andAbsorber for the SPring-8 Storage Ring", ibid., 209.

100........
1-11000001~~..u..cu"--~..u..cu"--~..u..cu"--~...U.U."---~u..u.ul

0.001

0.01

0.1

110100Beam Dose [Ah]Fig. 6. The prodlct of the beam current (/) andbeam lifetime ( 't") versus the accumulated
beam dose.
Figure 6 shows the product of the electron-beam current (I) am
the beam lifetime ('t) versus the accumulated beam dose. The-361-