1. SAES Project: Combination of NEG module and sputter ion pump
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2. Objectives
To compare base pressure between a combination of NEG module and ion pump and only for ion pump, for a bake out vacuum system
Compare base pressure for different bake-out duration for these two configurations
Compare base pressure for a combination of NEG module and different ion pump (different pumping speed of ion pump)
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3. SAES NEG Module CapaciTorr-D 2000 MK5 Alloy type: St 172
Getter Alloy Mass : 225g
Getter Surface : 1900 cm²
Pumping speed (l/s):
2000 l/s (H2) and 1000 l/s (CO)
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4. NEG Module
Cartridge: The Capacitor cartridges are configured in the form of sintered porous disks of St172. These sintered porous bodies are arranged in the cartridge structure in a way to optimize speed and capacity performances.
Pump Body: The optional pump body is a simple double flanged nipple
Heater: The heater of the D 2000 consists of a tantalum wire spiral wound on an alumina element supported by a stainless steel rod. This heater is part of the pump cartridge structure.
Thermocouple: The thermocouple is a K type electrically insulated within an alumina tube. It is assembled on the support flange and connected to the electrical connector with compensated contact terminations.
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5. Ion pump Ion pumps selected for this project:
StarCell 400l/s and StarCell 200l/s
StarCell 75 l/s and StarCell 40 l/s
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6. Project description
Systematic evaluation of NEG module and ion pump combinations: ultimate vacuum pressure and test for shorter bake out duration.
Task list:
Construction of a dedicated vacuum system
Pumping speed measurement of each ion pump
Pumping speed measurement of the NEG module
Calibration of the system and base pressure
Influence of baking time at 150°C for 5 different values of pumping speed with and whithout NEG module
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7. NEG Module Pumping speed measurement
Pumping speed measurement of the NEG module with a Fischer-Mommsen dome :
Injection of H2 and CO gas
SNEG (l/s) = C (l/s) (αΔP1/ΔP2 -1) – S turbo(l/s)
With the conductance C : C= 34.4 l/s for H2 and C= 9.19 l/s for CO
With the calibration SVT1/SVT2, α = 0.85 for H2 and α = 1 for CO
ΔP = P - P initiale
P= P x SN2/SH2 pour H2 et P= P x S N2 /S CO
Sensibility
S N2
S H2
S CO
SVT1 43
16.35
36.64
SVT2 34
16.42
28.97
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8. NEG Module Pumping speed measurement
S (l/s) for H2
S (l/s) for CO
NEG activation
45min at 450°C
1990 l/s
936 l/s
24 h at 450°C
2201 l/s
1530 l/s
SAES data: 2000 l/s (H2) and 1000 l/s (CO) for 45min at 450°C activation
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9. Vacuum test stand
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10. Vacuum test stand
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11. Influence of the bake out duration
24 hours,12 hours, 6 hours and 3 hours
Bake out température :
250°C for stainless steel vacuum chambers
250°C gate valve DN150CF
250°C NEG module
300°C ion pump
350°C VGI gauges and residual gas analyser
140°C injection valve
200°C valve on the turbo pump
Ion pump: 400 l/s
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12. Test procedure(1)
Venting of the system 15 hours (except NEG module which stay under vacuum)
Pumping of the system+ leak detection+ open gate valve to pump NEG module
Start bake out (300°C)
At the end of the maximum temperature level, reduction of the temperature at 180°C for gas analyser and B.A.G gauges and 150°C for the rest of the vacuum system
Flash of the ion pump
Degasing of the B.A.G gauges 45 min at 50 mA
Degasing of the R.G.A 45 min at 20 mA
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13. Test procedure (2)
At the end of the degasing, activation of the NEG module 45 min at 450°C
Degasing 5 min and start gauges and gas analyser
Start ion pump
Close valve on the turbo pump and injection valve
Stop bake-out
24 hours after the bake out stop, note pressure of the two BAG gauges and save a scan
Close the gate valve, wait 30 min and note the pressures and save a scan.
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14. Results of the base pressure without NEG module
Base pressure with 400 l/s ion pump
Bake out duration
hours
P1 (torr)
P2(torr)
24 h at 300°C 1, 1,
12 h at 300°C 1,
6 h at 300°C 1,
3 h at 300°C 1,
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15. Results of the base pressure with NEG module activated
Base pressure with combination of NEG module and 400l/s ion pump
Bake out duration
hours
P1 (torr)
P2 (torr)
24 h at 300°C 0, 1,
12 h at 300°C 0,
6 h at 300°C 1,
3 h at 300°C 1,
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16. Mass scan after bake-out
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17. Influence of the bake-out temperature
Bake out duration:
6 hours
Bake out température :
150°C for stainless steel vacuum chambers
140°C gate valve DN150CF
150°C NEG module
150°C ion pump
350°C VGI gauges and residual gas analyser
140°C injection valve
150°C valve on the turbo pump
Ion pump: 400 l/s
The same procedure as before was applied. we only reduced the temperature of the bake-out to 150°C except for the gauges and gas analyser
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18. Influence of the bake-out temperature
P1 (torr)
with NEG
activated
P2 (torr)
without NEG
300°C
6 hours 1, 1, 1,
150°C 3, 1, 2,
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19. First conclusions
1.We have the same pressure for all the different bake-out duration:
P= 1, torr only with ion pump (gate valve closed)
P= 1, torr with NEG module and ion pump
2. We have the same base pressure at 150°C and 300°C for a 6 hours bake-out duration with and without NEG module
3. We have the same base pressure for a 24 hours bake-out duration at 300°C and for a 6 hours bake-out at 150°C with and without NEG module.
It is possible to reduce duration and temperature of bake-out to achieve the same base pressure.
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20. Influence of other parameters
Bake out
150°C,
6 hours
P1 (torr)
with NEG
activated
P2 (torr)
without NEG
NEG under vacuum during air venting, TLabo=28°C 3, 1, 2, 1,
NEG air venting 3, 1, 1,
NEG under vacuum during air venting,
T Labo =20°C 3, 1, 1,
NEG activated during all the bake-out duration (6 hours) 4, 2, 1,
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21. Modulation of the gauges
Modulation of the two Bayard-Alpert gauges SVT1 and SVT2
Pressure before modulation:
P1= 2, torr
P2= 1, torr
After 20 minutes of modulation:
For SVT1: Pres= 1, torr (high value!)
For SVT2 : Pres= 3, torr
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22. Modulation of the gauges
Problem with SVT1: leakage current
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23. Outgasing rate of the vacuum system
1.When the gate valve is closed (only ion pump)
P= 1, torr
Q= P.S= (1, x 100)/0,45=3, torr.l/s (pour H2)
2. When the gate is opened (NEG + ion pump))
P= 1, torr
Q= P.S= (1, x 2000)/0,45=6, torr.l/s (pour H2)
Conclusion: The base pressure of this vacuum system is limited by the outgasing of the gate valve.
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24. Base pressure measurement
Remove the gate valve.
Bake-out at 300°C for 24 hours with the same procedure as before.
Measure 24 hours after bake-out stop:
P1= no value or torr (without modulation factor)
P2= torr
(P2= torr with the gate valve)
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25. Mass scan for base pressure
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26. Next steps
Precise measurement of the pressure of the two gauges for the base pressure.
Calibration of the two gauges and gas analyser using the gas injection line.
Change the 400 l/s for the other smaller ion pumps and compare the measurements.
Continue pumping speed measurement on the Fischer Mommsen dome for the different ion pumps
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27. Thank you for your attention
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