Miniature High Vacuum Pumps for Analytical Instruments

Miniature High Vacuum Pumps for 

Analytical Instruments 

Robert Kline-Schoder 

Paul Sorensen 

Copyright © 2007 

Creare Incorporated 

An unpublished work. All rights reserved. 

MTG 07-09-2597 - 1

Turbomolecular Pump Advantages 

• Supply clean vacuum at high flow rates 

• Pump all species, including noble gasses 

• Small size and mass 

• Potential for low power consumption 




MTG 07-09-2597 - 2

Creare Miniature Vacuum Pumps 

• Miniature Turbomolecular Pump 

– 4 L/s pumping speed (air) 

– 1x10 8 compression ratio (N 2 ) 

– 3-12 W power consumption 

– 10-12 Torr discharge pressure 

– 550 g mass 

– 100,000 RPM rotor speed 

• Extremely Miniaturized Turbo-drag Pump 

– 4 L/s pumping speed (air) 

– 1x10 8 compression ratio (N 2 ) 

– 3-12 W power consumption 

– 10-12 Torr discharge pressure 

– 130 g mass 

– 200,000 RPM rotor speed 




MTG 07-09-2597 - 3

Miniaturizing TMPs Is a Challenge 

• TMP Tip Speeds 

– Must be significant fraction of the mean molecular speed 

– For a 2.5 cm pump, speeds > 200,000 rpm are needed 

– This can lead to: 

• Reduced bearing life 

• High power consumption 

• High stresses in rotor 

• Rotor/Stator Clearances 

– Must be large enough to accommodate manufacturing tolerances 

and vibration 

– Must be small enough not to degrade pump performance 




MTG 07-09-2597 - 4

Design Efforts 

• Miniaturization requires optimization of: 

– Motor 

– Turbo-pump rotor and stator 

– Molecular drag stage 

• Analytical optimization efforts include: 

– Electromagnetic analysis of motor 

– Structural analysis of pump rotors 

– Bearing life analysis 

– Modeling of turbo and drag stage pumping performance 

at small size scales 




MTG 07-09-2597 - 5

Experiments Complement Analysis 

• Testing is necessary to complement design 

efforts and verify analytical models: 

– Motor (bearing and lubricant) life tests 

– Tests of alternative magnet designs for motor 

– Bench tests of individual turbo- and drag-pumping stages 

– Testing of completed pumps 




MTG 07-09-2597 - 6

Measurements Verify TMP Blade Model 

16 

14 

Data 

Calculation-Radial leakage correction 

Calculation-No radial leakage correction 

Compression Ratio 

12 

10 

8 

6 

4 

70 80 90 100 110 120 130 

Rotor Speed (KRPM) 




MTG 07-09-2597 - 7

Measurements Verify Drag Pump Model 

Comparison of Model to Data for Sleeve 2 

Pressure Difference, Torr 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 

0 1 2 3 4 5 6 

Data 

Calculated 

Inlet Pressure (Torr) 




MTG 07-09-2597 - 8

Structural and Magnetic FEM Results 

structural analysis used to 

optimize blade geometry and 

material choice 

magnetic analysis used to 

optimize magnet choice and 

minimize power losses 




MTG 07-09-2597 - 9

Exploded View of Final Design 

Pump housing 

Pump Stator 

DC motor 

Pump rotor 




MTG 07-09-2597 - 10

Fabrication Is Challenging 

• Maintaining tight tolerances during machining 

and assembly: 

– Must balance desire to minimize inter-stage leakage using 

small gaps with need to make pump fabrication practicable 

• Balancing rotors 

– Particularly important at high speeds demanded by 

miniature TMPs 

– Creare has devoted substantial resources to developing a 

capability to balance at operating speeds 




MTG 07-09-2597 - 11

Precision Machining and Assembly 




MTG 07-09-2597 - 12

Compression Ratio Test Setup 

Creare Motor 

Controller 

High Vac: 

Compression Ratio Test Data: CO 2 

Vacuum Pressure CO 2 

Compression Ratio CO 2 

1.00E-05 

1.00E+08 

- 40 °C 

Vacuum Pressure [Torr] 

1.00E-06 

50 °C 

22 °C 


1.00E+07 

1.00E+06 

22 °C 

50 °C 

1.00E-07 

- 40 °C 

0 2 4 6 8 10 12 

1.00E+05 

0 2 4 6 8 10 12 

Foreline pressure [Torr] 

Foreline Pressure [Torr] 




MTG 07-09-2597 - 14

Compression Ratio Test Data: He 

Vacuum Pressure He 

Compression Ratio He 

1.25E-05 

1.00E+07 

1.05E-05 

- 40 °C 

Vacuum Pressure [Torr] 

8.50E-06 

6.50E-06 

4.50E-06 

50 °C 


1.00E+06 

22 °C 

50 °C 

2.50E-06 

22 °C 

5.00E-07 

- 40 °C 

0 2 4 6 8 10 

1.00E+05 

0 2 4 6 8 10 

Foreline pressure [Torr] 





MTG 07-09-2597 - 15

Flow Test Setup 

Bleed valve 1 

Gas: He, CO 2 

and Air 

Low Vac: 

1 mtorr 

P 1 

Convectron 

Metering Orifice 

Creare Motor 

Controller 

High Vac: 

Flow Test Data: CO 2 

7.0 

Pumping speed vs vacuum pressure 

CO 2 

Pumping speed [L/sec] 

6.0 

5.0 

- 40°C 22°C 50°C 

4.0 

3.0 

2.0 

1.0 

0.0 

1.00E-07 1.00E-06 1.00E-05 1.00E-04 

Vacuum pressure [Torr] 




MTG 07-09-2597 - 17

Flow Test Data: He 

7.0 

Pumping speed vs vacuum pressure 

Helium 

Pumping speed [L/sec] 

6.0 

5.0 

4.0 

- 40°C 22°C 50°C 

3.0 

2.0 

1.0 

0.0 

1.00E-06 1.00E-05 1.00E-04 

Vacuum pressure [Torr] 




MTG 07-09-2597 - 18

Power Draw Data: CO 2 

DC Power Draw CO 2 

-40 deg C +50 deg C +22 deg C 

DC Power [W] 

12.00 

10.00 

8.00 

6.00 

4.00 

2.00 

0.00 

0 2 4 6 8 10 12 





MTG 07-09-2597 - 19

Power Draw Data: He 

DC Power Draw He 

-40 deg C +50 deg C +22 deg C 

DC Power [W] 

12.00 

10.00 

8.00 

6.00 

4.00 

2.00 

0.00 

0 2 4 6 8 10 





MTG 07-09-2597 - 20

Summary 

• Designing and building an effective miniature vacuum 

pump is a highly interdisciplinary effort (mechanical, 

thermal, fluid, and electrical requirements) 

• Analysis crucial for balancing competing requirements 

• Experiments are essential to qualify models and verify 

performance 




MTG 07-09-2597 - 21

Miniature High Vacuum Pumps for Analytical Instruments

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