JAERI-Conf

95-021

PA23
Conditioning of Positive Inflector Voltage for
The Injection of Negative Ions at TARN-II
K. Chida, T.Tanabe, M.Yosizawa, Y. Arakaki,
T. Morimoto and !.Katayama
Institute for Nuclear Study, University of Tokyo
Midori-cho, 3-2-1, Tanashi, Tokyo 188, Japan

Abstract
An ultrahigh vacuum of the order of 10- 8 Pa ~ hasbeen kept to obtain sufficient beam life times for thebeam experiments at TARN-II. Recently, positive highvoltage was applied to inflector electrodes to injectH- ion beam in the ring. In this case, vacuum pressurerose up to the order of 10- 6 Pa and residual gas components of CO and C02 remarkably increased. We tried
to get a required inflector voltage at normal vacuum
pressure by conditioning the electrodes. As a result,vacuum pressure was improved to 1.2x!0- 8 Pa at highvoltage of +44 kV.
1. Introduction

An ion storage/cooler synchrotron with an electron
cooling system TARN-II has been operated for thestudies of atomic physics and accelerator technology[!].
Vacuum pressure of the order of lxl0- 8 Pa
is required to get sufficient beam life times for thebeam experiments. The ring has a hexagonal shape with
six long straight sections and has a circumference of
78 m. Ion beams from an SF cyclotron are transported
through a beam line and injected into the ring by anelectrostatic inflector system which was originally
Septum Electrodeused at the former storage ring TARN [2,3].
Recently, positive high voltage, as well as usual
negative voltage, was applied to the inflector
electrodes to inject H- ion beam. Initially vacuum
pressure increased to the order of to-sPa.
We triedto get the inflector voltage required to inflect thebeam at a normal vacuum pressure by conditioning theelectrode.
2. Electrostatic inflector
The inflector system is composed of successive one
pair of electrode with an arc length of 300 mm and agap of 8 mm. Amean radius of curvature is 5005 mm
and an inflection angle is 6.9'.
The septum
electrodes are made of tantalum foils of 0.1 mm thick
and are earthed to ground potential. The high voltage
electrodes are made of stainless steel and supported
by ceramic insulators. Designed maximum electric fieldat the gap is 100 kV/cm. Three beam probes are inserted at upstream, middle and downstream of theelectrodes. The inflector system is shown in Fig. 1.
3. Conditioning
Usually, vacuum pressure of the order of 10- 8 Pa hast

To Vacuum Pomp

( 0.1 mm Ta foil )0Movable Base Plate

100

200300Fig. 1. The plan and side view of the electrostatic inflector.
-88-400

SOOmm

JAERI-Conf 95-021

been kept at the beam time in which negative highvoltage of about 30 kV was applied to the electrodes(for example 10 MeV-HeD+). However, when positivehigh voltages were applied to the electrodes, a hugeamount of outgassing occurred and the vacuum pressure
at the long straight section (Sl) in which inflector
electrodes are equipped inrireased to the order of
10- 6 Pa. Main outgassing was observed at thedownstream inflector (inflector 2) and any change ofvacuum pressure was not observed while a high voltageof +60 kV was applied to the upstream electrode(Inflector 1).
In order to improve the deterioration of vacuum,
two aging processes were applied to the electrodes.
1) positive high voltage aging.
When a high voltage of +60 kV at the inflector 1
was applied, electric leakage current was lower than
0.1mA and any change of vacuum pressure was not observed. On the other hand, at the inflector 2, a highvoltage was applied gradually to +45 kV. At this voltage, electric leakage current was 1.3 mA and vacuum
After recovery ofpressure increased to 10- 6 Pa.
1x10- 7 Pa, the highoforderthetovacuum pressure
a conditioning
SuchkV.
48tovoltage was increased
10 hours peraboutofinterval
theatwas performed
conditionduringday. An example of vacuum pressure
when highpressuresing is shown in Fig. 2. Vacuum
shown byareoff
voltage swiched on and swiched(A,B,C) and (1,2,3), respectively.
Improvement of the vacuum pressure by conditioning
Vacuum pressures of HV onis shown in Fig. 3 (A).
to the pressurescorrespond
3Fig.
inand HV off shown~r---------------------~.

~a.

i";g·UJ-7

r·l
AlJlJ
2I08C

2448

-J0I

72

T !ME (H)Fig. 2. An example of vacuum pressure at an aging
time.
at (1,2,3) and (A,B,C) in Fig. 2. The accumulation
time while high voltage was applied to the electrodes
was shown as aging time. The total conditioning timeof 100 hours was achieved with positive high voltage.
The vacuum pressure was then decreased from 10- 6 Pa to5.3x10- 8 Pa at high voltage of +48kV and from 1.4xl0- 7
Pa to 1.2x10- 8 Pa at +44 kV.
2) Negative high voltage aging.
Total conditioning time of 200 hours was achieved
while a high voltage of -60kV were applied to theResults areboth electrodes, inflector 1 and 2.
The vacuum pressure
shown in Fig. 3 (B).
decreased from 3.5xl0- 7 Pa to 7.2x!0- 8 Pa at a highvoltage of -60 kV and from 1.5xl0- 8 Pa to 1.0x10- 8 Pa at-30 kV.
In the case of positive high voltage aging,residual gas spectra at the high voltage on (A) and(B)
(A)

-6
10-8
10lO.

f1)
f1)

0.

~

0.

01-wlf)

•~

lfl~
lf)

-9-7lf)-7

iii0. 10

10ii!100.

......

-60 KY

01-.-------w

0:48 KV

n:-8

r- 10-6P(HVON)•••••••-91- 10••••••••••••-SOKYo--30 KV-1010-8-810 •10~~~~~~=-~----~• ••• • P ( HV OFF)_,_1-1010"'A

1-I-2x10•• • • •-11-92X10050100

AGING TIME (H)

IQI
100200AGINGTJME(H)

Fig. 3. Improvement of the vacuum pressure in the inflector chamber
by appling positive (A) and negative (B) high voltages.
-89-JAERI-Conf 95-021

off (B) were measured. Results after aging times of30 hours are shown in Fig. 4. Variations of theresidual gas components by the aging are listed inTable I. Ratios of ion current at HV on and HV off,I(on}/I(off}, are remarkable for the outgas components of CO and C02 at the aging time of 30 hours.
However, the ratios decreased by a factor of 4 after
85 hours.
Table 1 Variations of the residual gas
components by the aging
M/e 2Gas Aging Ion current(au) I(on)/I(off)time(H) HV off HV on

16 182844co(B)

H2CH4H20

coC0230
8530
8530
8530
8530
85

3.0x!0- 7 !O.Oxl0- 7 3.3
3.0x10- 7 3.7x!0- 7
1.9
3.4xt0- 9 2.6xlo-s 7.6
3.5x10- 9 1.0x1o-a
2.9
5.5xto-s 4.6xto-s 8.4
5.0xlo-s 1.3x1o-a
2.6
1.2x1o-a l.7x!0- 7 14.2
1.3xlo-a 5.0x1o-a
3.9
6.7xto-s l.1x10- 7 16.4
7.0x10- 9 3.0x!0- 8
4.3

CO aM/e 2

16 1828

HV OFF44

We deduce that some oil vapor condensed on theelectrode and the insulator, because the temperatureof the inflector was lower than other parts of thevacuum chamber during the baking time.

Fig. 4. Mass spectra of the residual gas in the chamber at positive high voltage on (A) and off(B) after
aging time of 30 hours.

4. Conclusion

References

1) When positive high voltage was applied to the infleeter electrode to inject H- ion, remarkable outgassing occurred and vacuum pressure increased to theorder of to-sPa.
2) Improvement of vacuum pressure was achieved byconditioning the electrodes with positive and negativevoltages. For example, vacuum pressure was improved
from 1.4xl0- 7 Pa to 1.2xl0- 8 Pa at operation voltage of+44 kV.
3) We deduce that high residual gas components of COand C02 come from pump oil which sticked to low temperature place during baking time.
Baking at atemperature as uniform as possible for the whole system is important.

1] K.Chida et al., "Present status of TARN-II vacuum
system" Vacuum 44(1993)539
2] T. Hattori et al., "Beam Transport System from the
INS-SF Cyclotron to TARN" INS-NUMA-25(1980)
3] F.Soga et al., "Beam Transport and Injection Systemfrom the SF Cyclotron to the TARN-II Synchrotron
Cooler Ring" INS-T-494(1990)-90-