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 Primary vacuum Electronics, cables, etc. Thin foil

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 (H 2 O): –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) 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 Valve 1 Valve 2 Primary pumpTurbo pump Bellow Secondary vacuum Primary vacuum Restriction

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