1. Leak Detection method for Vacuum Systems Alexander Permogorov 2.3.2016

2. Overview Variety of leak sources Variety of leak sizes Different methods for different sizes Division based on achievable pressure

3. Pressure and solution Achievable pressureDetection Method Few tens TorrAcoustic* Few mTorrHelium + Thermocouple/Ion Gauge Below 10 -4 TorrHelium + Leak Detector * “Leak Detection”, N. Hilleret, CERN, Geneva, Switzerland [https://cds.cern.ch/record/455564/files/p203.pdf]https://cds.cern.ch/record/455564/files/p203.pdf

4. Helium spraying http://www.heliumleakdetection.net/Helium-Leak- Testing/what-is-helium-leak-detection.html Light and high diffusion rate Non-reactive Relatively cheap Highly available

5. Helium + Thermocouple/Ion Gauge Helium partial pressure larger than air Detectable Difficult with large setups

6. Leak Detector Leak Detector = Mass Spectrometer Detect even small leaks Connected to the pump

7. Leak Detector * “Leak Detection”, N. Hilleret, CERN, Geneva, Switzerland [https://cds.cern.ch/record/455564/files/p203.pdf]https://cds.cern.ch/record/455564/files/p203.pdf

8. Conclusions Leaks coming from a lot of possible places Different location – different rates Different rates – different method

9. Leakage rate The leakage rate of a vessel having a volume of 1 cubic meter is 1 Pa m 3 s -1, if the interior pressure increases or decreases by 1 Pa within 1 second. * * https://www.pfeiffer-vacuum.com/en/know-how/leak-detection/general/leakage-rate/https://www.pfeiffer-vacuum.com/en/know-how/leak-detection/general/leakage-rate/

10. Acoustic method of detection Pressure limit of few tens Torr Most common causes: Missing or corrupt O-ring Flange malfunction High-pitched whistle heard at the leak * Possibility of ultrasound detectors usage ** * https://www.lesker.com/newweb/technical_info/vacuumtech/leakdetect_01_overview.cfm?section=leakshttps://www.lesker.com/newweb/technical_info/vacuumtech/leakdetect_01_overview.cfm?section=leaks ** “Leak Detection”, N. Hilleret, CERN, Geneva, Switzerland [https://cds.cern.ch/record/455564/files/p203.pdf]https://cds.cern.ch/record/455564/files/p203.pdf

11. Pirani Gauge Heat transfer measured. A wire (filament) is heated with electric current until thermal equilibrium is achieved. Gas molecules take away thermal energy from the filament, therefore under the same current wire has different temperatures depending on gas pressure (lower pressure -> higher temperature). Temperature change causes resistance change which is easily detected. This type of gauge can be used to measure pressures from 10 -4 Torr to 0,5 Torr. * http://www.idealvac.com/files/brochures/Pfeiffer_PKR_251_P irani_ColdCathode.pdf * “A User's Guide to Vacuum Technology”, J. O'Hanlon, Wiley-Interscience, 3rd Edition(2003) 2003, 516 pp.

12. Pirani gauge (Continued) In the figure: Circuit for operating Pirani Gauge in Constant current mode Helium is sprayed around suspected leaks Helium has a known response by the Ion Gauge Since Helium is light and diffuses fast, so its partial pressure in the chamber is higher than air partial pressure given the same exposure time. For lager leaks acetone can be used (for testing O-rings and flanges), as it has a very high response http://drkfs.net/pirani.htm

13. Ion Gauge http://www.pchemlabs.com/product.asp?pid=4515 http://philiphofmann.net/ultra highvacuum/ind_iongauge.html

14. Ion Gauge (Continued) Filament is an electron source Remaining gas molecules in the system get ionized inside the cylinder Ions are collected by the wire in the middle and thus pressure is measured Pressures between 10 -4 and 10 -11 mbar. http://philiphofmann.net/ultrahighvacuum/ind_iongauge.html

15. Ion Gauge as Leak Detector Helium is sprayed around suspected leaks Helium has a known response by the Ion Gauge Since Helium is light and diffuses fast, so its partial pressure in the chamber is higher than air partial pressure given the same exposure time. Relative sensivity of Ion Gauge * “A User's Guide to Vacuum Technology”, J. O'Hanlon, Wiley-Interscience, 3rd Edition(2003) 2003, 516 pp.

16. Leak Detector He-tuned mass-spectrometer Atoms coming from the pump ionized with e-beam Ion paths are bent with constant magnetic field (heavier ions bent less) A diaphragm allows only He ions to pass Passed ions are then collected This kind of detector can detect even smallest leaks in orders of 10 -9 torr*liter/sec or even down to 10 -11 torr*liter/sec