CONTROL OF THE TRISTAN VACCUM SYSTEM
H.Watanabe, K.Kanazawa and H.Ishimaru
National Laboratory for High Energy Physics
Oho-machi, Tsukuba-gun, Ibaragi-ken, 305, Japan
ABSTRACTINTRODUCTION

The TRISTAN vacuum system is controlled bycomputers and program controllers. All components
for the system were miniaturized as possible.
Four types of ion pump made from aluminum alloy
were used at the pressure range less than lo-4 Pa.
Pressure measurement from an atmospheric pressure
to lo-10 Pa were made by pirani gauges, convectrongauges, inverted magnetron gauges, and modulating
ion current gauges. (MIG)

For the vacuum system of the TRISTAN accumulation
ring (AR) the required base pressure is 10-8 Pa without
beam and lo-7 Pa with beam. The beam life time isdependent not only on the total pressure but also
on the atomic and molecular species in the residualgases. It is therefore very important to analyze
residual gases as well as to measure the totalpressure. Gauges to measure the total pressure arerequired to have a wide dynamic range from 10-9 Pa toan atmospheric pressure which is utilized to a safetyinterlock for system protection. The dynamic range
is covered by four types of gauge in our controlsystem. The control and the data aquisition aremade using computers and a programmable controllers (PC).

NO. fTerminal

CONTROL SYSTEM
highwcy~b.2

Principles of the design for the system are:Controls and measurements are all made by computers,
Interlock by hardwires is made by a programmablecontroller,
3 Power supplies and gauges are miniaturized as possible
without meters.
Fig.l shows utilized states of the computer.
CAMAC is used as an interface. Significant signals
for the maintenance of the system were connected
to Interlock Input Resister (IIR) which can bealways interrupted. Many connectors from data
terminals make it possible to use computers in theAR tunnel and the auxiliary rooms. Fig.2 shows anexample of interlock system by hardwires.
12le m•nal
Equipment

1l R

CAMAC

Fig. 1

Interlock lnput Registers 1G

Status Input Gate

SOR

Status output Register

ADC

Analog to Digital Converter

Equipment

The vacuum chambers in electron storage rings arecooled to suppress temperature rise due to synchrotron
radiation. A sensor of a water turbine type is used
to check the flow rate of cooling water. Beam can be
stopped at the value less than 80 % of the flow rate.
Platinum resistors are used to measure the temperatureof the chambers.

Utilized states of the computer.

Gate valve

Pironi ·gouge
Convectron gouge
Inverted rnognetron cold cathode gauge
Modulating ion current hot cathode gouge
Mass filter
Sputter ion pump

Fig. 2

Example of interlock system by hardwires.

256

Controllers of the 2 types of gauge are mounted on
a NIM 2 unit module which can operate 4 gauges.
Figs.4 and 5 show output characteristics of the two gauges.

CONTROL OF THE PUMPS
Four types of pump are used in the TRISTAN AR:
Rotary pumps and turbomolecular pumps (TMP) forroughing, sputter ion pumps (SIP) for ultra highvacuum, and non-evaporable-getter (NEG) for evacuationof hydrogen.

>Roughing pumps are used for the evacuation froman atmospheric pressure, to start up SIP and forthe gas desorption due to synchrotron radiation.
Only the roughing pumps are manually controlled inthe AR. Four types of SIP are 500 1/s, 30 1/s,
10 1/s, and 250 1/s distributed ion pumps (DIP).

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Power supplies for SIP are ver4 small because startup pressure is set at less than 10- Pa. There are
two types of the power supply, 5.5 kV, 20 mA typefor the pumps 125 1/s or more and 5 mA type for thoseless than 125 1/s. A NIM 2 unit module contains one
20 mA type or two 5 mA types. Type of the power
supplies is a DC-DC converter. Fig.3 shows thepower supply.

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10Pressure ( Pa)Only discharge current of DIP can be measured
because both an anode and a cathode of the pump are
insulated from the chambers. The current can beutilized to measure the pressure.

Fig. 4

Roughing pumps and SIP are controlled withcomputers and PC. The NEG pump can evacuate onlyhydrogen in room temperature mode. Activation is
manually controlled.

Output characteristics of the Pirani gauge.

->8.........

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CONTROL OF THE GATE VALVES/:JThe dual flat mirror surface seals with differential
pumping type gate valves are used not to disturb
wall current and not to excite parasitic modelosses. To operate the valves a roughing pump anda SIP (10 1/s) are required. The valves, theroughing pump, and the SIP are automatically controlled
by PC.

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1/,110./10.3

10Pressure( Pa)
Fig. 5

Output characteristics of the Convectron gauge.

Medium and high vacuum ranges (10-l - 10- 7 Pa)
An inverted magnetron gauge is used to cover thevacuum range because the gauge has a wide dynamic range
and less mode jump2 than other cold cathode gauges.
The output characteristics is shown in Fig.6. Though
it can be operated in an atmosphere, the operation lessthan 1 Pa is prefered. The reason is that a long operation in low vacuum accellerates contamination. The gauge
controller is mounted in a NIM 2 unit module which cancontrol 2 gauges.

Fig. 3 Power supply for SIP, 20 mA (left) and two 5 mA.
TOTAL PRESSURE MEASUREMENT
Low vacuum range (10 5 - 10-l Pa)

UHV range (lo-7 - lo- 10 Pa)

Gauges to cover the low pressure range are aconvectron gauge (GP) and pirani gauge of constantcurrent type. A convectron gauge is chosen because
the pressure around atomosphere can be measured. Thegauge is set at the back of a TMP. Contact output of
the gauge is used to an interlock of a roughing pump.
A pirani gauge of constant current is set to a chamberand sends an interlock signal less than 1 Pa.

A Modulating Ion Current (MIC) gauge is used tocover this range. Merit of the gauge is that the signal
component and the desorbed gas bombarded by electrons or
secondary particles excited by electron beam can be separately detected. A guage head is shown in Fig.8. The
gauge controller can be operated at the distance closer
than 200 m from the gauge head.

257

Total pressure

2.7 x 10-5 Po

Beam current

65 rnA-Total pressure

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16 9 ~~~~~~~~~~~~~~~~~

107

105

103

161 104

105

Fig. 9Mas patterns with beam.

Fig. 10Mass patterns without beam.

tAlPressure (Pa}Fig. 6166

Beforeiljec!ITOutput characteristics of the cold cathode gauge.

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Beam onr---1\7.

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Fig. 7.

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Cold cathode gauge and the controller.

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16 5-Total pressure

Fig. 11

Partial pressure change with beam conditions.
CONCLUSIONS

Fig. 8Gauges and power supplies of pumps of the AR aredeveloped under a new idea of all computer control andminiaturization. The gauges, power supplies, and computercontrolled system have been operated without any significant trouble. Simpler and more reliable control system
for the main ring has now been designed including
computer controlled roughing system.

Head of the Modulating Ion Current gauge.
RESIDUAL GAS ANALYSISREFERENCES

In storage rings, it is very important to know thecomposition of the residual gas species to estimate thelife time. A mass filter with SEM is used for a residualgas analyser. The mass filter for ultra high vacuum hasa function of electron bombarded degassing. Distance
between a gauge head and a controller is about 100 m.
Output of six species can be selected by a peak detecter
and read with analogue values. Typical mass patterns
with beam and without beam are shown in Fig.9 and 10.
Fig.ll shows partial pressure at before injection, during
injection, and after injection. 70 % of residual gases
is Hz and the quality of the vacuum has been improved.

12258

H.Ishimaru, et.al., Journal of the Vacuum Society ofJapan, No.4, 25, 1982, 184.
P.A.Redhead, et.al., Physical basis of ultra highvacuum, Chapman and Hall Ltd., London, 1968.