Vacuum tests

1
Vacuum tests

• Problem description
• Valve presentation
• Test setup
• Measurements Results
• Conclusions

2
Problem description

• Separated primary and secondary vacuum to obtain
  good ring vacuum
• Thin foil required because of multiple scattering
• Intrinsically safe solution is desired

Secondary vacuum
Thin foil
Electronics, cables, etc.
Primary vacuum
3
Valve presentation

• Valves that react to differential pressure
• Electric/Pneumatic, but
• Fail-safe solution required
• Proposal Gravity controlled valve

4
Test setup

• Leak rate during normal operation (with/without
  pump)
• Preliminary
• Dynamic response to sudden pressure changes
  (leaks)
• System behavior during pump down

Removed picture of vacuum test setup
5
Test setup (2)
Sander Klous 24-11-2000
6
Measurements Results

• Conductance (H2O)
• 10-3 liter/sec without dedicated pump
• 10-5 liter/sec with dedicated pump
• Expected secondary vacuum pressure 10-4 mbar
• This would result in
• 10-9 mbar l/s leak-rate

Pumping slots
7
Measurements Results (2)

• Dynamic response
• Maximum differential pressure over the valve is 6
  mbar
• Measurement is dominated by the bellow
  configuration (see picture)
• More realistic measurements are required with
  faster gauges

Removed picture of tandem (gravity-controlled)
valves
8
Measurements Results(3)
Secondary vacuum

• Pump down time
• Conductance between primary and secondary vacuum
• Bellows (L 1 m, d 20 mm)
• Maximum pressures in range of the gauges 500
  mbar, calibrated with a baratron.
• 3 hours to around 1 mbar
• (?p 9 mbar at 500 mbar)
• 3 hours to 10-5 mbar

Bellow
Primary vacuum
Restriction
Valve 2
Valve 1
Primary pump
Turbo pump
9
Conclusions

• All measurements indicate the gravity controlled
  valve can work
• For the correct dynamic pressure analysis a more
  realistic setup is required