Outline

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Outline

• Vacuum production
• Vacuum measurement
• Vacuum materials and hardware

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ideal vs. real surfaces
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Vacuum
Otto von Guericke (1602 - 1686)
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Vacuum
1 Pa 1 N/m2
1 torr 7.5 ?10-3 Pa
1 atm 101385 Pa ? 105 Pa
1 mbar 102 Pa
1 torr 0.75 mbar
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Mean free path
ltvgt?t
High pressure gt mean free path much smaller
than container dimensions gt gas behavior
dominated by intermolecular interactions gt
continuum flow
Low pressure gt mean free path larger than
container dimensions gt collisions with walls,
statistical flow, no viscosity gt molecular flow
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Main pump types
Compression pumps
Condensation or adsorption pumps
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Roughing pumps
oil-sealed rotary pump
pumping speed 0.5-3 l/s
pressure range 103 - 10-3 mbar
oil-free membrane pump
pumping speed 0.3-1 l/s
pressure range 103 - 1 mbar
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Diffusion pump
effective in molecular flow regime
backing pump needed
momentum transfer to gas molecules through
collision with directed jet of oil molecules
oil with low vapor pressure
pumping speed 5000-50000 l/s
pressure range 10-3 - 10-8 mbar
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Turbomolecular pump
effective in molecular flow regime
backing pump needed
pumping speed 50-1000 l/s
pressure range 10-1 10-10 mbar
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Bis hierher am 25.06.2009
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Cryo pump
sublimation frequency
bath cryopump
LN2
refrigerator cryopump
LHe
LN2
pumping speed 1000-100000 l/s
pressure range 10-3 10-10 mbar
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Sublimation pump
?
getter filaments
LN2
getter elements are highly reactive and bind gas
molecules in stable compounds
sublimable getters Ba, Mg, Al, To, Ti
cooling increases pumping speed (higher sticking
coefficient and active surface)
pumping speed up to 10000 l/s (depending on
surface area, pressure, time)
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Ion pump
cathode
anode
cathode
permanent magnet
implantation getter
HV 4-7 kV
memory effect for noble gases
pumping speed 50-500 l/s
pressure range 10-3 10-10 mbar
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Pump operation range
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Vacuum measurement
Membrane vacuum meter
Capacitance manometer
vacuum
vacuum
reference
reference
FA(p2-p1)
C ? A/d
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temperature sensitive
pressure range 103 10-2 mbar
pressure range 103 10-6 mbar
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Pirani gauge
pressure
?
R
gas density
?
thermal conductivity
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filament temperature
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filament resistance
vacuum
pressure range 102 10-3 mbar
calibration needed
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Ionization gauge cold cathode (Penning)
pressure range 10-3 10-10 mbar
calibration needed
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Ionization gauge hot cathode
pressure range 10-3 10-10 mbar
calibration needed
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Partial pressure measurement quadrupole
Mass filter
-


-
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stable trajectory
?
electric fields ?
40Ar equivalent to 20Ne
28CO equivalent to 28N2
pressure range 10-5 10-11 mbar
calibration needed
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Further uses of quadrupole mass spectrometer
Leak detection
Mass filtering (e.g. in particle sources)
Thermal Desorption Spectroscopy
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Pressure meter operation range
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Typical UHV system
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Common vacuum problems
1. Improper cleaning techniques 2.
Backstreaming 3. Virtual leaks 4. Leaks 5.
Incompatible materials
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Construction Materials compatible with UHV

• OFHC copper, also pure copper
• Be-Cu alloy, phosphor bronze
• 304 SS (non-magnetic), 310 series SS, 340 SS
  (magnetic)
• Teflon (gassy, compressible)
• MACOR (machinable glass composite)
• 6061 Al (essentially pure aluminum), 2024 Al
  (harder alloy)
• quartz, pyrex (gassy)
• alumina (careful with glazed ceramics)
• molybdenum, tungsten
• "mu-metal" magnetic shielding (Co, Ni, Fe)
• polyimide (Vespel)
• Sn-Ag solder

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Vacuum cycle
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Vacuum connections HV
p ? 10-6 mbar
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Vacuum connections UHV
ConFlat (CF) system
p lt 10-10 mbar
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Motion in UHV
linear motion
rotation
bellow
magnetic
bellow
magnetic
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UHV gates
gate valve
bellow
butterfly
electrical feedthrough