The 9th Symposium on Accelerator Science and Technology, Tsukuba, Japan 1993

Test of the Vacuum Chamber with NEG Stripfor the ATF Damping Ring
Nobuhiro Terunuma, Ken-ichi Kanazawa, Yo-ichiro Hori and Junji Urakawa
National Laboratory for High Energy Physics
1-1 Oho, Tsukuba-shi, Ibaraki, 305, Japan
Abstract
Design study on the vacuum system for the damping
ring of the Accelerator Test Facility (ATF) is in progress.
This ring has eight wiggler magnets. The vertical gap between poles is 20 mm. We are going to install NEG strip
on both side of a beam duct in this narrow gap. In the activation of the NEG strip, heating problem for the chamber
wall will be considered. We design the support of the NEG
strip and test the vacuum performance of the chamber withNEG strip.

NEG Strip

I~~I.

69

Beam Duct\\©I

NEG Strip
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T.I C~oling Channell

69

214mm

I. INTRODUCTION

SS316LClamp

The damping ring in ATF is an electron ring ( 1.54GeV, 600 rnA) to achieve a low emittance beam using wiggler magnets. There are two wiggler sections in the ringand each section has four wiggler magnets. Hard intense
synchrotron radiation (SR) will be generated by wiggler
magnets. The maximum power density of it at the beamduct wall will reach 1.44 kW /m, and the photon density
will become 1.9 x 10 19 photons/m/s.
An aimed average pressure of the ring is below 5 x
10- 8 Torr with beam. To realize this pressure, we mustachieve the pumping speed of 140 lfs/m along the duct.
The distributed pump along the beam duct is essential to
get this pumping speed. We are planning to install ZrV-Fe (St707) non evaporable getter (NEG) strips [1] as amain pump for the wiggler chamber.
All vacuum chambers are made by aluminum alloy(A6063) and they are extruded in atmosphere of Ar +0 3 . The aperture of the beam duct is a race-track of 15
mm high x 47 mm wide and its length is 2.1 meter for one
wiggler magnet. The cross sectional view of the chamber isshown in figure 1. Along the beam duct, two side channels
for NEG strips will be installed.
In this paper we briefly report the first result of thet.est of the installation of strip into a vacuum chamber simulating the pumping channel.

Ceramic Bearing
AL-Stopper

Details of the NEG strip assembly

Figure 1. Cross sectional view of the wiggler chamber.

II. SUPPORT OF THE NEG STRIP
Activation of the NEG strip is performed by dire<;tcurrent heating. In this process, the strip is heated at450 °C for 50 minutes. Therefore, the strip must be isolated from the chamber wall to avoid the over-heating of
the chamber and that of wiggler magnets. Cross sectionalview of the chamber and the support without the strip isshown in figure 2.

Figure 2. Cross sectional view of the chamber and theNEG support.

-193-Figure 3. NEG strip with supprts and a copper braid.

Aperture of the test chamber is a rectangular of 15 mm
high x 70 mm wide. It is the same as that of the sidechannel for the wiggler chamber. The NEG strip is 800 mm
long and 30 mm wide. Its expansion length to the directionof the strip becomes about 6 mm in the activation.
At a half height of the chamber, ceramic bearings aresettled on the support rods. Rods are made of stainlesssteel (SS316L) and they are arranged every 110 mm along
the chamber. Ceramics isolates the strip from the chamber
wall to avoid over-heating of the wall and electric short
between the strip and the wall. One edge of the NEG strip
was fixed with the copper clamp to connect an electrical
power feed~through. Other edge was not fixed and it wasconnected to the chamber with a copper braid and clamps.
Ceramic bearings rotate smoothly against the expansion of
the strip. Therefore, the NEG strip can move toward to thecopper braid without touching the chamber wall. Figure 3
shows the photograph of the NEG strip with supports andthe copper braid.

III. ACTIVATION TEST
A. Set up and pre-bakeout

Figure 4 shows the schematic diagram of the experimental set up. Test chamber is 1.7 meter long and it
includes two NEG strips. We attached the thermocouple
on the NEG strip to measure temperature. The chamber
was evacuated by a turbo-molecular pump (TMP, 300 1/s)
and an ion pump (IP, 30 1/s). One B-A gauge measured
the total pressure in the head of the pumping port.
At first we had baked the vacuum chamber to 150 °C
for 24 hours. About 20 hours evacuation after the bakeout, the total pressure became 1.0 x 10_ 9 .Torr with TMP.

Vacuum Chamber

300Vs
Turbo
Pump

Rotary Pump

Figure 4. Schematic of the experimental set up.

Before the activation of the NEG strip, we had purged
the chamber with pure N2 gas and had connected the ion
pump. It was a same sequence of the ring construction.
Chambers will be baked before assembly at the beam line,
but will not be baked in situ. An hour evacuation fromthe N2 purge, the pressure becomes 1.6 x 10- 7 Torr withTMP.
B. Activation of the NEG strip

The NEG strip was activated at 450 °C for 50 minutes
by fed ding the current of 50 A. About 18 hours evacuation
after the activation, the total pressure becomes 2. 7 X 10- 9
Torr with TMP and IP.
.
Normal operation of the vacuum system for the damping ring will be performed with IPs and NEG strips. Therefore we closed the valve and separated TM P from the-194-

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t-TMP o~1o· 9 ~~WU~L-~WU~L_~WUllill
1000
100
101

---------··r··----------·--------·········

10·10~~~UW--~~~~~~~

1

Pumping time (min)

10100

1000

Pumping time_ (hr)Figure 6. Pressure variation vs pumping time for theultimate pressure measurement.

Figure 5. Pressure variation vs pumping time.

chamber to study this situation. After 10 minutes fromit, the total pressure became 8.4 x 10- 9 Torr. However,the pressure with only NEG strip was increased up to9.0 x 10-s Torr as shown in figure 5. It was a build-upof CH 4 because the NEG strip had very low pumping efficiency against CH4.
Four hours later, the total pressure became 8.9 x 10- 9Torr with a combination of the NEG strip and IP.
C. Heating of the chamber wall

During the activation, we had been checked the temperature of the outer wall of the chamber, because thedistance between the wall and the heated NEG strip wasonly 7 mm. We expected the over-heating problem forthe chamber. Before the activation, the temperature ofthe chamber was equal to the room temperature "'25 °C.
At the end of the activation, the temperature of the wall
ranged from 30 to 75 •c. The maximum one was obtained
at a position correspond to a half length of the NEG strip.
The heat isolation was successful and we can allow this order of the over heating for vacuum chambers and magnets.
D. Ultimate pressure of the chamber

We measured the ultimate pressure of the vacuumchamber with the NEG strip. After the above test, wecarried out a bakeout of the chamber as shown in figure 6.
At the end of the bakeout, we performed the activation for
the NEG strip and the conditioning for IP. After 40 hours
evacuation we obtained the pressure of 1.6 x 10- 10 Torrwith the NEG strip, IP and TMP.
After 90 hours evacuation the ultimate pressure forthe system with a combination of the NEG strip and IP
was obtained as 3.6 x 10- 10 Torr.

IV. SUMMARY
The vacuum test of the chamber with NEG strips for
the ATF damping ring was performed. Aperture of thetest chamber is a rectangular of 15 mm high x 70 mm
wide and it included two NEG strips with supports.
The over-heating of the chamber wall was checked during the activation of the NEG strip (450 °C). The maximun
temperature of the wall reached 75 •c near the center position of the strip. It was found that the design of the NEG
supprt were acceptable.
Before the activation of the NEG strip, we baked thechamber, purged it with pure N2 gas and connected theion pump to simulate the ring construction in near future. About a day evacuation after the activation, thetotal pressure of the chamber with the NEG strip and IP
was obtained as 8.9 x 10- 9 Torr.
Finally, the ultimate pressure of the chamber was measured. Chamber baking and NEG activation was continuously performed without vacuum breaks. After 90 hours
evacuation, the ultimate pressure was 3.6 x 10- 10 Torr witha combination of the N-EG strip and IP.

REFERENCES[1] manufactured by SAES GETTERS S.p.A., !tally.

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