STATUS OF ELECTROSTATIC SEPARATORS AT KEK
Harumi Ishii and Akira Yamamoto
National Laboraotory for High Energy ~hysics
Electrostatic separators with built-in high voltage generators ·~ere developedfor the secondary beam lines of the 12 GeV proton synchrotron at KEK1). They
have been operated stably since they had been installed in the beam lines. Themaximum field of 1005 KV I 10 em was achieved in the latest one (Mark II-2) whose
aperture of the field of 10 cmg x 40 cmw x 6 m1. The performance of the electrostatic separator is given and the characterist1c s of vacuum breakdown in theregion of lo-4 Torr is also discussed.
Performance
All of the separator have been operated in the beam lines at the electricfield between 600 kV I 10 em and 900 kV I 10 em. The performance of the latest
separator which is more compact than!that of the initial type of the KEK separator(Mark I) is given in Table 1. The maximum field of theis separator was
1005 kV I 10 em with the spark rate of 0.3 sparks I min .. The continuous
opration has been performed at the field of 900 kV / 10 em with the spark rate of
1 spark I h in the beam line. The pressure dependence of the breakdown voltage(P-V curve) is shown in Fig. 1. Helium and Neon .(35%-65%) gas mixture is flowed
to adjust the pressure. The continous operation is performed in the pressure
range of a few times of 10 -4 Torr.
Characteristic of Vacuum Breakdown in This Region
The breakdown voltage in the region of 1o-5 10~ Torr depnds on the pressureof the residual gas. This effect has been studied by tbe authors et al2).

1000

900000?00

P-VCURVEDCSEPARATORMARK IjJ.}FORBUBBLECHAMBER LINE/IIil

EU:CTRO!EPOSITIVE .:_----SUS 304
NEGATIVE -----An. AI
GAP --------100 mm
GA$--------Ne- He ( :~;.~'!4)

i l/~~~7~=~~ION~NG ~~~:EMV•25•10"• Toraa,//"___#-/·\-·-· ·-"-;-1 ... 2 ~rlll/ft

Electrode gap
w1dthlength.

-•

Oct.H

1 --·

Nov. 6-·-"

Nov.lt~lectrodeI6m

Pressure plateau at

stainless steel
anodised aluminum
1005 kV I 10 em
0.3 I min
900 kV I 10 em
1I ha few days
2 x 10- 6 Torr /day
1 x lo- 3 Torr

working field

900 kV I 10 em

positivenegative
Madmum field
Working field·--;:::"--,;....·-10 em
40 em

Material

spark rate////.-.?

•oc/l!

I

Table 1, Performance of theelectrostatic separator(Mark 11-2).

spark rate
Conditioning time
Deconditioning rate andSupport insulator.. o~.• ------~..~,o-~.------~~o~-.-------7,,~,o-~.-------,~~·..
PRESSUAE(Tor1'1Fig. 1, Pressure depandence of.the breakdown
voltage at the electrostatic separator(Mark II-2).

-259-dimension

10 an (o.dJ) x 20 Cllllllterfal

ceramic (A1 203J

H. V. genera tors
dimensions ( x. y. z )lUX ilium H. V.

stability

20 x 72 x 70 m 3+600 ltV

lo- 4

The following relationship between
the maximum voltage (V) and thepressure (p) was found by ourexperiments,

I800

V = V0 + kp

,0600/Ar·,c?

.
./0.......-

0Ne-He(65%-35%)/0_-"

He---------'X----------)(

where V0 is the maximum voltage att" ' __....-"
cthe ultra low pressure ( lo-6) and>k is a coefficient. Figure 2 shows"'~400P-V Curve of Mark II I
the pressure dependence of the15 em
gap:"'"'..,"'
45 Clllw x 2 m1
area:
maximum voltage for the various
anode: stainless steel
gases at the separator Mark III with gcathode:anodised aluminum~200
the gap of 15 em and the length of2 m. The k is the function of thegas material. In fig. 3 , the08-4
10410
maximum voltages are plotted as theJ[TorrPressurefunction of the atomic mass number
at the pressure of 1 x lo-4 Torr.
Fig. 2, Pressure dependences of the breakIt seems to be understood as thedown voltages for the gases of Ar,
nearly linear function in this mass
Ne-He and He at the separator Mk-III.
region for the innert gases.
The useful gas for theelectrostatic separator should not
700
be chosen by only the above
relationship but by also the theeffect of the critical pressure
where gaseous discharge is initiated.
600
The effect of the critical pressure.
is discribed elsewhere.
Neon and helium gas mixture waschosen as the optimised gas for theKEK separators.
~X0> 400

Summaryx"'
The electrostatic separators
01020
with built-in high voltage generators
4030CNe-He)
He. Arhave been operated staby in the beamlines and the no problem have happened
Atomic Mass Number
during these two years. The working
Fig. 3, Mass number dependence of the breakfield of 900 kV I 10 em is asatisfactory result in this developdown voltage at the pressure ofment.
1 X 10- 4 .
.r;References

1) A. Yamamoto, A. Maki and A. Kusumegi, Nucl. Instr. and Methods 148 (1978) p.203.

2) A. Yamamoto, A, Maki, Y. Maniwa and A. Kusumegi, Jap. J. App1. Physics 16 No.2
( 1977) p. 343.

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