1

Institute of Metals and Technology, Ljubljana, Slovenia

Calibration of extractor gaugesdown to 10-12 mbar

Janez Šetina, IMTjanez.setina @imt.si

Sefer Avdiaj, Lotrič d.o.o.

Bojan Erjavec, IMT

2

Institute of Metals and Technology, Ljubljana, Slovenia

PRINCIPLE OF CONTINOUS (DYNAMIC) EXPANSION METHOD

Primary flowmeter

• constant pressure-variable volume

• constant volume-variable pressure

S

G

Gas flowmeter

QOrifice C P

dtVPd

RTQ )(1mol/s][ ×

×=

dtdV

RTPQ ×=

dtdP

RTVQ ×=

)1( BRCQRTP +××=

RB≈ 0.01 to 0.05

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Institute of Metals and Technology, Ljubljana, Slovenia

Ultimate pressure of dynamic expansion system

S

G

Gas flowmeter

QOrifice C

P

Inner surface area of calibration vessel: A1

Area of the orifice: A0

To assure Maxwellian distribution of molecules:

A0/A1 <<1/1000 (typically 1/5000)

Achievable ultimate pressure in the calibration chamber:

Pult=q x (A1 / A0) / C0

calibration chamber 300 mm dia x 300 mm (V=20 L):

A1=3000 cm2, A0= 1 cm2

If q = 1x10-13 mbar.l/(s.cm2)

and C0=45l/s (H2 conductance of 1 cm2 orifice)

We get: Pult=7x10-12 mbar

4

Institute of Metals and Technology, Ljubljana, Slovenia

Published XHV calibration systems

K. Jousten, et all, Metrologia, 1999, 36, 493-497

PTB, GermanyKP2 – 10.000 L/s cryopump (2.7 K)

C2 – 100 L/s (N2)

XHV chamber – SS 316 LN vacuum fired (950ºC/2h)

however, reported ultimate pressure is only 9x10-12 mbar

5

Institute of Metals and Technology, Ljubljana, Slovenia

Li et al, J. Vac. Sci. Technol. A 28, 2010, 1099

Lanzhou Institute of Physics, China

two NEG pumps Capacitor B1300

"Maglev" turbo 2200 L/s

orifice – 100 L/s (N2)

XHV chamber – SS 316 LN vacuum fired (950ºC/2h)

reported ultimate pressure is 7.9x10-12 mbar

6

Institute of Metals and Technology, Ljubljana, Slovenia

Our system

Volume V2 = 5.5 L

Ci – 4.1 L/s (Ar)(calibrated in-situ using SRG1)

Gas flow adjustable through Leak Valve (LV)

Pumping speed of NEG (Capacitor D400): 400 L/s for H2 ((measuredmeasured inin--situ)situ)

EG1

SRG1

EG2

Ci

V2V1V0

LV

SRG2

CDG100

CDG1

Gassupply

Flow meter

CDG1000

Turbopump

Turbopump

Diaphragmpump

NEG

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Institute of Metals and Technology, Ljubljana, Slovenia

Flowmeter modes

V1V0

LV

SRG2

CDG100

CDG1

Gassupply

To calibrationchamber

Flow meter

CDG1000

1.1E-07

1.2E-07

1.3E-07

1.4E-07

1.5E-07

1.6E-07

Con

duct

ance

C /

(l/s)

1E-1 1E0 1E1 1E2 1E3Upstream pressure / mbar

Flowmeter is used in two modes:

P > 1x10-10 mbar: constant volume-variable pressure(pressure increase measured with SRG)

P < 1x10-10 mbar: "constant conductance" mode

8

Institute of Metals and Technology, Ljubljana, Slovenia

9

Institute of Metals and Technology, Ljubljana, Slovenia

0

2

4

6

8

Ext

ract

or re

adin

g /

E-1

2 m

bar

0 2000 4000 6000 8000 10000 Time / s

Controller_1 Controller_2

2

3

4

5

6

7

8

Ext

ract

or re

adin

g /

E-1

2 m

bar

24

24.2

24.4

24.6

24.8

25

25.2

T /

*C

0 1000 2000 3000 4000 5000 Time / s

Controller_1 Controller_2 Temperature

Exchanging of controllers has no significant effect on ultimate pressure readings

Controller 2 shows some correlation with temperature oscillations

RESULTS

10

Institute of Metals and Technology, Ljubljana, Slovenia

Switching on/of showed negligible outgassing of extractors(at 400 L/s pumping speed of NEG)

0

2

4

6

8 E

xtra

ctor

read

ing

/ E

-12

mba

r

0 1000 2000 3000 4000 5000 6000 Time / s

Ex_1 Ex_2

11

Institute of Metals and Technology, Ljubljana, Slovenia

Repeatability of generation of very low Ar calibration pressures

1.6x10-12 mbar and 7.8x10-13 mbar

2

3

4

5

6

7

8 E

xtra

ctor

read

ing

/ E

-12

mba

r

4000 6000 8000 10000 12000 14000 Time / s

Extractor 2 Extractor 1

12

Institute of Metals and Technology, Ljubljana, Slovenia

Results of calibration of two Extractor gaugesconnected to two different controllers: gas Argon

Extractor 1 Extractor 2

0.6

0.65

0.7

0.75

0.8

Cor

rect

ion

fact

or

1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6Ar reference pressure / mbar

EX1_Contr2 EX1_Contr1

10%

0.6

0.65

0.7

0.75

0.8

Cor

rect

ion

fact

or

1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6Ar reference pressure / mbar

EX2_Contr1 EX2_Contr2

10%

13

Institute of Metals and Technology, Ljubljana, Slovenia

Results of calibration of two Extractor gauges: gas Helium

4.6

4.8

5

5.2

5.4

5.6

5.8

6 C

orre

ctio

n fa

ctor

1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6He reference pressure / mbar

EX1_Contr2 EX2_Contr2

10%

14

Institute of Metals and Technology, Ljubljana, Slovenia

CONCLUSIONS

• Relative difference of calibration factor for two extractor gauges was <10%

• Linearity of both extractor gauges operated with controller #2 was within ca. 10% in the range from 1x10-12 mbar to1x10-7 mbar

• One of the readout electronics (#1) has some pressure dependence in the range from 10-9 mbar to 10-7 mbar

• residual indication (X-ray, ESD?) for one extractor gauge is at least 3x10-12

mbar

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Institute of Metals and Technology, Ljubljana, Slovenia

ACKNOWLEDGEMENT

Many thanks to Prof. Dr. Rudolf Dobrozemsky, TU Vienna, Austria, for giving us one of the extractor gauges.

Presented work was party financed by European Union, European Social Fund. Operation implemented in the framework of the Operational Programme for Human Resources Development for the Period 2007-2013, Priority axis 1: Promoting entrepreneurship and adaptability, Main type of activity 1.1.:Experts and researchers for competitive enterprises.