Experiment 10

Residual Gas Analyzer

Air Pumpdown

 

Objective: Experimentally observe the gas composition in a normal vacuum system pumpdown from air.

Reference: Module 12

Required Materials:

Varian Vacuum Trainer

Latex gloves

Residual Gas Analyzer

 

Experimental Procedure:

Students must wear latex gloves when handling vacuum components.

1. Insure that the system has achieved equilibrium at atmospheric pressure. With all valves closed, remove the bell jar and let stand for at least 15 minutes.

2. Visually inspect the base plate and gasket for cleanliness. If the gasket needs cleaning, wipe with alcohol. Dry thoroughly with a lint-free cloth and lubricate with a thin film of vacuum grease.

3. Place the bell jar and shield on the baseplate.

4. Close all valves.

5. Plug the traineer into the power outlet.

6. Turn both Mechanical and Turbo Pump toggle switches to the ON position.

7. Select the roughing gauge on the controller (TC1, Channel 1).

8. Check the gauge. It should be reading atmospheric pressure (7.6 on the +2 scale). Note: The TC gauge is not accurate above 1 Torr.

9. Open the foreline valve.  

10. Press START on the Turbo Controller Panel. Allow the Turbo Controller to come up to speed ( 75 K rpm) and indicate NORMAL OPERATION.

11. Close the foreline valve.

12. Open the roughing valve in one continuous motion. Note: The foreline and roughing valve should never be opened at the same time.

13. At 3 Torr, begin crossover operation by

- closing the roughing valve

- opening the foreline valve and waiting 10 seconds

- opening the high vacuum valve

14. Switch the gauge to BA (ION gauge). The gauge will begin operation when in range (<1 mtorr).

15. When the pressure reaches the midpoint on the 10-5 scale, turn on the residual gas analyzer. Refer to the operating manual for the RGA.

16. List the masses and the amplitude value for each mass.

17. Analyze the spectra and determine the species present in the volume.

Optional Steps:

18. Allow the vacuum system for an extended period of time (e.g. overnight).

19. Run scan at the base pressure.

20. Compare the masses and amplitudes of the two scans.