OPERATION OF THE TRISTAN VACUUM SYSTEM, INJECTION LINE AND ACCUMULATION RING
T. Momose, K. Narushima, H. Mizuno, K. Kanazawa, H. Watanabe, and H. Ishimaru
National Laboratory for High Energy Physics
Oho-machi, Tsukuba-gun, Ibaragi-ken, 30S, JapanINJECTION LINE
Injection line is a transport line between the 2.S
GeV linac of the photon factory(PF) and the accumulation
ring (AR). The line consists of the specially extruded
aluminum alloy vacuum chambersl. The line is 3SO m longand has two branches fore+ and e- (Fi~.l). It is divided into 12 sections by the gate valves . Each section
was evacuated by a turbomolecular pump· (TMP, SO 1/s),
and a rotary pump (RP). At a pressure of lo-4 Pa, a SO
1/s non-evaporable getter (NEG) was activated where thepump is operated at room temperature mode. Then operation of a 30 1/s sputter ion pump (SIP) was started.
A power supply for the SIP is a DC-DC converter type3.

ABSTRACTThe operation of the TRISTAN vacuum system is
described. Thermal gas desorption rate of the aluminumchambers was 10-9-lo-10 Pa.l/s.cm2 as expected fromthe bench test. Pressure rise due to synchrotron radiation was 7 X 10-S Pa/mA at 0.7 mA.hours and 3.2 X
10-8 Pa/mA at 4.7 A.hours. Beam energy dependence ofthe pressure rise was linear. No thermal problem due tosynchrotron radiation was observed. The corrosion due
to high energy radiation with the aid of humidity was
found in the aluminum windows for X and gamma rays.
Heating due to wall current discontinuity was occurredin a current transformer, ceramic chambers, and normal
viton seal type gate valves.

All the chambers including the SIP were virgin
where a helium leak check was applied. At the initial
operation of the SIP, the SIP were baked. During theoperation of the SIP no abnormal discharge was observed.
Pressure of the injection line after SO hour operation
was on the order of lo-6 Pa which is 2 orders better
than the required pressure (lo-4 Pa). Therefore wemeasured the pressure distribution of the line reducing
the numbers of the SIP from 10 to 4 as shown in Fig.l.
The pressure at one month after was the same with thatof 4 days after and still less than the required pressure. It must be mentioned however that if the pressure
is higher than l0-4 Pa load of the SIP could abruptlyincrease. Gas desorption rate at 10-6 Pa is on the4order of 10=9 Pa.l/s.cm2 which corresponds to the value
without baking. A baking (loo•c, S hours) was applied to
one of the sections of the line. During the baking nothermal problem was observed. After the baking the pressure was improved less than one order, but influenced
gradually by adsorption from other sections.

INTRODUCTION
The construction of the TRISTAN vacuum system(injection line and accumulation ring) which is thefirst all-aluminum alloy ultra high vacuum system wascompleted. The first beam was injected in October 1983.
Beam was stored at 2.SS GeV in November and was accelerated to S.2 GeV in December. In February 1984, theoperation of the internal targets was started. In June
beam was accelerated to 6.S GeV with the parallel operation of the normal and the superconducting cavities.
The obtained maximum beam intensity was 6S rnA for single bunch and 90 rnA for multi-bunches. Successful operation shows no substantial problem of the all-aluminumalloy vacuum system and gives us much valuable infor-mation.

The results obtained in the operation of the injection line were applied to the design of the transport line (300m) from the AR to the main ring (MR),that is, (1) no heater for baking, (2) only 3 pumping
stations for the line at stationary operation.

N-AR-Log P(Pa)-1~----------------~-2-3-4-5

E-2

Outage-7-8~~~~~~~~~

sw

NE-3

E-INJECTION LINE--4-1.,..-----------,
4-30 DAYSs-5-4 +------+-----~--:li-->'3 Ml N-5NEG
Power- 6 t-::::::;-;::;:rc:::;:=;--;:::::;-;::1-2-3NLog p(Pa)START-6-6on

2 3 45 6 7 8 9 10 11 12 13 14 fS 16 17 18

September
Fig.l

Layout of the TRISTAN vacuum system andpressure distribution.

Fig.2253

1983

Initial pumping curve of a section in the AR.

ACCUMULATION RING

The straight line in Fig.3 shows the result ofPETRA, where the chambers were prebaked at 150°C and precleaned by Ar discharge. Beam energy at PETRA can be varied from 5 to 19 GeV. Critical energy (Ec) of the synchrotron light is 1.44 KeV at 5 GeV. For the AR, £c is
1.59 KeV at 2.55 GeV. Taking account of a frequent operation at the lowest· energy, difference in factor 5 between the data could be from the pretreatments. The slopeof the line is -0.63 for PETRA, -0.74 at less than 103 mA
hours and -1.5 at 103 mA.hours or more for AR. The slopeof -1.0 before Ar discharge cleaning and from -1.25 to-0.7 after the cleaning were obtained at photon factory7,where a baking was applied. No explanation is obtained
for the scattered data of the slope. The change of theslope at 103 mA.hours can not be explained quantitatively
though difference in operation energy and beam intensity
are suggested. Deterioration about one order at 2200 rnA.
hours shows the influence of an exposure (11 sections)in an atmosphere for maintenance. Exposures of 1 section
are 2660, 3240, and 3390 mA.hours. The deterioration ofthe latter 2 cases is small compared with that of thefirst case (2660 mA.hours). This may due to the short
exposure less than 30 min. The data after 2200 rnllhours\iTere rearranged by resetting current time integral. The
obtained slope is -0.69 which is close to the value ofless than 103 mA.hours. Energy dependence of the pres~.
sure rise is shown in Fig_. 4. Linear dependence on beamenergy are obtained. Therefore we ..may expect a little
influence of the pressure rise during high·energy operation.
Raw data of gas species with beam at 1.7 mA.hours
are 38 (H 2 ), 12 (CO), 6 (co 2 ), and 1.5 (H 20). The ratio
is constant at a pressure range between 1.3 x lo-4 and6.5 xlo-6 Pa. The data without beam are 0.8 (Hz), 0.2(HzO), 0.17 (CO), and less than O.Ol(COz) at 1.7"mA;hours.
At 18 mA.hours, the data with beam are 70 (Hz), 23 (CO),
10 (COz), and 4 (HzO). No significant change in the ratio
was shown at the two different current time integral.
These data were obtained in the baked section. Beam life
time at 20 mA.hours was 103 sec at 2 x 10- 6 Pa and 2 x
102 sec at 1.3 x lo-5 Pa for the be~m intensity of on
the order of rnA. The result was compared with the theoretical values. The comparison showed that the number ~f
an equivalent charge was between 14 and 16. The lifetime at 4.7 A.hours was 75 min at 5 mA and 2 x l0-7 Pa.
It can be approximately said that the life time of theAR increases with a square root of current time integral.

The AR which has a circumference of 377 m is divided into 12 sections by the gate valves2. Roughing pumps
are 12 50 1/s TMP. Main pumps are 56 distributed ion
pumps (DIP, 250 1/s) in bending magnet chambers (Bchambers). Sub-pumps are 70 SIP (30 1/s) and 70 NEG(50 1/s). 3 RF cavities are set in one of the 4
straight sections.An RF cavity has a roughing pump (2501/s, TMP) and a main pump (2 x 500 1/s, SIP). Pressureof 8 sections in the arcs reached to 10-6 Pa after 1week evacuation using only sub-pumps. 10-8 Pa was obtained in some of the sections using main pumps without~ baking and discharge cleaning. Thermal desorption
rate was on the order of 10-10 Pa.l/s.cm2 at the pressure without baking4.
A baking was applied 2 times to the section (Sl)which includes 5 sets of a quadrupole and a bending
magnets. The pressure change related to the first baking
is shown in Fig. 2. Within 3 hours after the baking, ·theNEG were activated and operation of the SIP was started
without trouble.
DIP was tested for 2 hours where thepressure was on the order of 10-6 Pa. During the test,
magnetic field was 3.6 K Gauss and the chamber was ·evacuated by roughing pumps. The peak pressure was on theorder of lo-2 Pa. The test showed that the dark current
was on the order of ~ with no magnetic field and highvoltage applied. Therefore the pressure of each section
was measured using cold cathode gauges3.
Dynamic gas desorption
The required pressure without beam is satisfied.
However the required pressure with beam ·(lo-7 Pa) is notsatisfied because of the pressure rise due to synchrotron light, that is, photo-induced gas desorption (dynamic gas desorption). Fig.3 shows the pressure rise as
a function of beam current time integral, where the data
are based on the pressure of 8 sections in the arcs. At
the end of July 1984, it was estimated that about 104mA.hours were necessary to get the required pressure.
It may take about 1 .year to get the target. Therefore
it is interesting to know if the_ pressure rise ·could be
reduced by applying pretreatment on chambers. Electronbombardment 5 and RF discharge6.have been tested on chambers of the MR.

AR AI Chamber 6063 EX"""' -5<( 10Ex167

00..:

3"""'
<(Beam Current
Time Integral.E00..:( A·h)

2.75 3.33

2Ql.!!!
a:~:JIllIll~0..:I
BeamFig. 310Current

Time Integral

103(mA·h)

Pressure rise of the AR as a function of a beam current
time integral.
254I2345
Beam Energy ( GeV)
Fig. 4

Energy dependence ofthe pressure rise.

An influence of humidity was observed with the highvoltage connectors for SIP and DIP. It was estimatedthat humidity accelerated abnormal discharge at the connectors and that an insulator was carbonized and metal
was oxidized by the discharge. This trouble can be overcome by reducing the humidity in the AR tunnel.

Table 1
Peak heights of the gas species from the nomal
gate valve
beam intensity(rnA)

H2010154.595
100

peak heights (arb. unit)co 2H20co0216170
320

3.5llOllO

0.5510Maximum power of synchrotron radiation at B-chamberis 940 W/m at 6.5 GeV and 20 mA (e-)8. Each bellows at
both sides of a B-chamber receives power about 100 W. To
protect bellows (0.3 mm), a 5 mm Al cylinder (absorber)
was welded inside chambers so as to make a shadow onbellows. Since critical energy of the radiation at 6.5
GeV is 28 KeV, penetration depth is 2.8 mm and 83 % ofthe radiation (80 W) can be absorbed at the cylinder.
The role of the absorber has been already confirmed bya radiation test using high energy electron beam ofequivalent power and penetration depth9. In fact, nothermal trouble was observed in the bellows.

0.5
35
35

Wall current
In electron storage rings, electron beam excites
wall current inside the beam chambers. Therefore we paid
attention for the continuous current flow. The gate
valves used in the AR satisfy the continuous current
flow for both cases, open and close. They are so called
dual flat mirror surface seals with differential pumping type gate valves2. No influence of the wall current
was observed on these gate valves.

Power due to synchrotron radiation is 0.27 MW at
6.5 GeV and 20 rnA (e+, e-). 0.88 tons/min of coolingwater is necessary if l0°C temperature rise were admitted. A cooling set consists of 2 bending and 2 quadrupole magnets. Therefore there are 34 sets in the AR.
Cooling pipes (inner diameter, 8 mm) are isolated fromother metal using polyethylene tape to prevent galvaniccorrosion. Total amount of the cooling water is now 0.3
tons/min at the flowing rate of 8 1/min. Temperature of
the water was sometimes set below dew point. Therefore
the dew was observed on the aluminum alloy chambers.
Humidity control is necessary more strictly.

We were obliged to use the normal viton seal typegate valves to isolate the superconducting cavity in theAR. The valve has discontinuous structure for the current
flow. Therefore beam intensity was less than 8 rnA when
the cavity was set in the AR. Peak heights of the residual gases from the gate valve during the operation are
shown in Table 1. The dual flat mirror surface seals
gate valves can be applied to the superconducting cavity
for the next operation.
A pressure was deteriorated to 10-2 Pa because acurrent transformer (CT) to monitor beam intensity washeated at more than 20 rnA of single bunch. The pressure
deterioration at 30 rnA started after about 30 min of thecurrent build up. This was also a problem of wall current. The CT is a kind of a coaxial cavity and has a gap
about 5 mm to cut wall current. In addition, permalloyand glass wool were included in the cavity. There was noproblem after the CT was eliminated.

CONCLUSIONS.
The all-aluminum alloy ultra high vacuum system(the injection line and the accumulation ring) has been
operated without any substantial trouble. High reliability andperformance of the aluminum vacuum system wereproved, Much valuable information was given to improve
the operation of the AR and has been applied to the design of the MR,

Ceramic chambers for kicker magnets also showed theheating problem. The chamber is a rectangular cylinder
having a race-track type hole. Inside surface of thehole, Ti-Mo coating was applied to maintain the continuous current flow. The coating is 2 )Jm so that the magnetic field can be inside the hole. Temperature was, forexample, 77°C at the both edges and 54°C at the centerof the chamber for single bunch and 1 hour operation of40 rnA. The heating was due to a discontinuity of metal
coating between the coated Ti-Mo film and the metallized
bellows at the both edges. It was repaired by an improved evaporating source of Ti-Mo.

REFERENCES
1.
2.
3.
4.
5.

Corrosion, humidity, and cooling system
6,Molybdenum internal targets have been used to produce gamma ray. 240 W synchrotron light is radiated on atarget at 6,5 GeV and 20 mA. An independent coolant wasused for the target cooling system. After 1 month operation, deposition of Cu and precipitation of aluminumhydroxide were observed on the surface of an aluminum
cooling pipe. It was estimated that Cu came from a copper heat exchanger in the coolant. Therefore the target
cooling systems are now connected to the AR cooling sys.tem.

7p

8.
9,

An extraction window (80 )Jm, Al) is at the down
stream of the target. After 48 hour operation of the internal target mode (5 GeV, 6 rnA), aluminum hydroxide wasobserved on the outer surface of the window. This can bemade by the high energy light with the aid of humidity
and N2 gas. Therefore the window was changed to a Beplate (0.3 mm) and the plate was covered with anAl foil
(80 )Jm). Helium gas was introduced into the space between the Be-plate and the Al-foil. A similar fact wasalso found in a X ray window.

255

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Aluminum Chambers by Microwave Discharge", this proceedings.
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