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�Generation of vacuum (pumps):ᴥ pumping systems
�general considerations on their use and “match” with physical quantities introduced for the dimensioning of vacuum systems
�Vacuum (pressure) measurements:ᴥ vacuum gauges
�general considerations and use:– Total pressure gauges,
– Partial pressure measurements.
Generation of vacuum (pumps) and Generation of vacuum (pumps) and Generation of vacuum (pumps) and Generation of vacuum (pumps) and
measurementsmeasurementsmeasurementsmeasurements
Vacuum technology
Classification of pump systems: Classification of pump systems: Classification of pump systems: Classification of pump systems:
pressure rangespressure rangespressure rangespressure ranges
Vacuum technology
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Main characteristics of pumpsMain characteristics of pumpsMain characteristics of pumpsMain characteristics of pumps
Vacuum technology
�Working pressure range
�Starting pressure
�Inlet pressure (max)
�Outlet pressure (max)
�Ultimate pressure (check the conditions).
�Pumping Speed S=S(p, M, or chemical)
�ThroughputQ = Q(pin, pout, M, gas).
�Compression factor (K=Pout/Pin) K=K(Q,ppv) on datasheet you’ll find K0 for Q = 0 (ideal), direct use for Pu, but for Q ǂ 0 check provided curves as K(ppv) or K(Q) if available.
Vacuum technology
Rough or back pumping SystemsRough or back pumping SystemsRough or back pumping SystemsRough or back pumping Systems
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Vacuum technology
Rotary mechanical pumpsRotary mechanical pumpsRotary mechanical pumpsRotary mechanical pumps
High compression factor (1 stage 105 , 2 stages 107), but …care on water problem and back-streaming
Vacuum technology
Oil lubricated system:Oil lubricated system:Oil lubricated system:Oil lubricated system:
316 mbar@ 70 °C
Solution: Ballast, Solution: Ballast, Solution: Ballast, Solution: Ballast,
in order to in order to in order to in order to injectinjectinjectinject air at the exaust air at the exaust air at the exaust air at the exaust
Oil provides also good sealingand works as cooling liquid, but
Oil is in the volume where gas is compressed.
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Vacuum technology
Oil pumps: the backOil pumps: the backOil pumps: the backOil pumps: the back----streaming streaming streaming streaming
problemproblemproblemproblemStart HV pump, before,pump which compresses
the oil in between HV pump
And rotary pump
Warning: when turbo has to be stopped, air has to be fed (automatic vent), during the deceleration of the turbo
to avoid back streaming
Characteristics Curves: one stage Characteristics Curves: one stage Characteristics Curves: one stage Characteristics Curves: one stage
systemsystemsystemsystem
Vacuum technology
Pumping speed Immediate use
Spb (S back pump)
Time of evacuation, Immediate use directly connected:
P=Poe -(Sp/V)·t
with bellow or connection:parametrized (D4/L) plot Sp vs t/V
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Vacuum technology
Characteristic Curves: Characteristic Curves: Characteristic Curves: Characteristic Curves: twotwotwotwo stage stage stage stage systemsystemsystemsystem
Dry Dry Dry Dry SytemSytemSytemSytem
Vacuum technology
Movement of gas in a scroll mechanism
12 3
456
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INLETOUTLET
FIXED SCROLL
ORBITING SCROLL
GAS
• Gas displacement with roto-traslation movement of a
moveing spiral on a fixed spiral.
• Pu Pirani measurement :
0,01 mbar
• Application: Oil free.
• Limited capacity of pumping vapors and chemical gases, liquids are dangerous for the
pump.
• Useless for industrial application, escludind load –
lock systems.
Maintenance after 8.000-10.000 hours
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Vacuum technology
Dry pump scroll: characteristic curvesDry pump scroll: characteristic curvesDry pump scroll: characteristic curvesDry pump scroll: characteristic curves
Vacuum technology
Membrane dry pumps:Membrane dry pumps:Membrane dry pumps:Membrane dry pumps:
• Transfer gas pump which make use of the oscillation of a
membranes or diaphragms.
• Pu in system with at least two stage: 1 mbar
• Oil free pumps.
• Available model with teflon protection of volume and parts
exposed to the vacuum for aggressive or corrosive
chemical processes.
Non return check-valve
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Vacuum technology
High vacuum pumping systemsHigh vacuum pumping systemsHigh vacuum pumping systemsHigh vacuum pumping systems
Vacuum technology
CryoCryoCryoCryo----
pumpingpumpingpumpingpumpingBased on the principles of
cryocondensation,Cryo-sorption,
andCryotrapping:
decreasing the surface temperature of systems exposed to the vacuum
the processes are favored,depending on the physical and chemical properties of
the gases present in the vacuum.
At T < 20 K for most
gases Pv not higher than 10-11 Torr
At T = 4.2 K H2 gives
Pv 10-7 Torr
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�Cryo-condensation (interaction between molecules): for gases increasing the coverage of a surface a saturation equilibrium is reached between adsorption and desorption.ᴥ Corresponding gas pressure in vacuum: vapor pressure curve.
p = Q/S + pvap
�Cryo-sorption (interaction of molecules with surfaces): submonolayer surface coverage experience attractive van der Waals forces exerted by cold surfaces:
ᴥ as consequence H2 can be cryosorbed at 20 K, and all gases may be cryosorbed at their own boiling temperature (1 bar).
�Cryotrapping: Cryotrapping is sorption process by which non-condensables gases are trapped in the growing solid-liquid condensation layer
of a condensable gas microcrystallites, while others are incorporated within the
crystallites. This method traps non-condensable molecules.
Terms for Terms for Terms for Terms for cryopumpingcryopumpingcryopumpingcryopumping
Vacuum technology
AA 2011/2012 Vacuum technology
High pumping speed for H2O and H2
Back pumprequired for
starting pressure (< 10-3 ) mbar and
regeneration.
Careful use of oil pumps?Poisoning of surfaces by
oils.
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Vacuum technology
UHV pumpsUHV pumpsUHV pumpsUHV pumps
TurboTurboTurboTurbo----molecularmolecularmolecularmolecular pumpspumpspumpspumps
Vacuum technology
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Vacuum technology
Turbo molecular pumping SpeedTurbo molecular pumping SpeedTurbo molecular pumping SpeedTurbo molecular pumping Speed
For pressure lower than --- we can assume in our calculation a constant pumping speed, and we can be safe for stable
working conditions.
Compression factor (KCompression factor (KCompression factor (KCompression factor (K0000)))) MK ∝0
Turbo pumps compress better heavy
molecules (oil ~ 70-75 amu)
For light molecules we have more
backstreaming.
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Vacuum technology
Camparison between turbo pumps and available Camparison between turbo pumps and available Camparison between turbo pumps and available Camparison between turbo pumps and available
informationsinformationsinformationsinformations�TurboVac T1600 TW1600 MagW1500S
�S�N2 1550 1420 1220�Ar 1410 1200 1180�He 1300 --- 1150�H2 720 --- 920
�K0
�N 2 5· 105 1· 107 1.5 ·108
�Ar 1· 106 3· 108 ---�He 1·104 --- ---�H2 2· 102 --- ---
�Pu < 3 ·10-10 mbar < 3 ·10-10 mbar 1 ·10-10 mbar
�Pout (N2)< 0.5 mbar < 8 mbar <0.2 mbar (air)
<2.0 mbar (water)
Vacuum technology
Sputter Sputter Sputter Sputter –––– getter ion pumps: getter ion pumps: getter ion pumps: getter ion pumps:
combine penning process and Ti trapping combine penning process and Ti trapping combine penning process and Ti trapping combine penning process and Ti trapping
Diode
Triode
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Ion sputter pumpsIon sputter pumpsIon sputter pumpsIon sputter pumps
Vacuum technology
Diode configuration is better for H2
Vacuum monitoring and control Vacuum monitoring and control Vacuum monitoring and control Vacuum monitoring and control
Vacuum technology
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Vacuum GaugesVacuum GaugesVacuum GaugesVacuum Gauges
Vacuum technology
� Direct measurements
� Indirect measurements
Vacuum technology
Direct measurementsDirect measurementsDirect measurementsDirect measurements
�Capacitance Manometer�Baratron
�Piezo
�Membranovac
�Diaphragm:
– High precision commercial
gauges 0.15.%
» 1100 -10-1 mbar
» 110 – 10-2
» 11 - 10-3
» 1.1 - 10-4
» 0.11 - 10-5
» MKS will be used (lowest P)
It measures the capacitance variaton due do the deformation of a wall (diaphragm).for the lowest pressure range displacement of 10-9 cm: thermal stability required.
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Vacuum technology
Indirect Indirect Indirect Indirect measurementsmeasurementsmeasurementsmeasurements
((((thermalthermalthermalthermal conductivityconductivityconductivityconductivity Gauge)Gauge)Gauge)Gauge)� Thermal conductivity gauge � Heat transfer depends on P, linear dependence for 0.01< Kn <10.
Heat transfer depends on P if T and accomodation parameters are constants.
leaks thermal
)( 41
421
+−= TTAH σε
High PressureLow pressure)(2
2 pd
kT
πλ =
Vacuum technology
Thermal conductivity gauge, with a Withstone bridge for a higher sensitivity.
PiraniPiraniPiraniPirani Gauge Gauge Gauge Gauge
Let’s start at a given P with the balanced bridge, if P increases, T of the filament R2 decreases (due to a higher heat exchange), the
bridge is unbalanced.
We can feed more current to keep T =cost (method)
Compensating tube is used for zeroing
at a P < 10-4 mbar.
Thermal conductivity dependes on the gas,
the read-out is calibrated for N2.
Vacuum vessel
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Vacuum technology
Accuracy 10%, in the range of more sensitivity, more or less for pressure in the range:
If R1 R4 = R2R3, thenIM = 0
T constant method: R2 ↓ if P ↑ , therefore Vdc (or V=Idc) ↑ then → T ↑ )
10-2 ÷102 mbar
Vacuum technology
Thermocouple gaugesThermocouple gaugesThermocouple gaugesThermocouple gauges
Thermocouple gauges also rely on the dependence of T on the
heat transfer due to P
Constant Current on a filament on Constant Current on a filament on Constant Current on a filament on Constant Current on a filament on
which center which center which center which center
a thermocouple si soldered.a thermocouple si soldered.a thermocouple si soldered.a thermocouple si soldered.
Therefore from the measurement of the T is possible to provide a
measurement of P.
Accuracy 30%.
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� In HV & UHV the particle density is so low , that it is non possible to detect the force exerted on a surface from the molecule impinging on it or the heat transfer.
Hot Cathode gauge
� It esploit the ionization of gas by electron bombardment and collection of the positive ion produced in the vacuum vessel
� The positive ion current collected is proportional to the density of particles in the vacuum vessel, to the electron current and to the ionization cross-section.
Vacuum technology
UHV gauges: UHV gauges: UHV gauges: UHV gauges:
ionization gaugesionization gaugesionization gaugesionization gauges
Hot cathode ionization gaugesHot cathode ionization gaugesHot cathode ionization gaugesHot cathode ionization gauges
Vacuum technology
Bombarding e- : ie
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Vacuum technology
� P(x) to be measured ( ) ( )( ) ( )2
2 NPxS
NSxP =
H2 0.42 - 0.45
He 0.18
H2O 0.9
N2 1.00
Acetone 5
Relative Sensitivity respect to N2
( )( )xgasofsensititylative
readingmeterPxP
Re)( =
� If normalized to Nitrogen S(N2) = 1.00
� Positive ion current i+=i p collected:
PiSi ep ⋅⋅=ie electron bombardment current, , , , P pressure, Ssensitivity (depends on ionization cross-section), Fixing S for nitrogen to 1.
AA 2011/2012 Vacuum technology
Disadvantages: higher selfDisadvantages: higher selfDisadvantages: higher selfDisadvantages: higher self----pumping due to sputtering 0.1 ~ 0.5 l/sec.pumping due to sputtering 0.1 ~ 0.5 l/sec.pumping due to sputtering 0.1 ~ 0.5 l/sec.pumping due to sputtering 0.1 ~ 0.5 l/sec.
Advantages: pressure range that connect hot cathode and TC. Advantages: pressure range that connect hot cathode and TC. Advantages: pressure range that connect hot cathode and TC. Advantages: pressure range that connect hot cathode and TC.
Penning Gauge
Thanks to the magnetic field the effective path length of the bombarding eThanks to the magnetic field the effective path length of the bombarding eThanks to the magnetic field the effective path length of the bombarding eThanks to the magnetic field the effective path length of the bombarding e---- is larger.is larger.is larger.is larger.
Cold Cathode ionizzation gaugesCold Cathode ionizzation gaugesCold Cathode ionizzation gaugesCold Cathode ionizzation gauges
High voltage (High voltage (High voltage (High voltage (1 kV) discharge induced by
cosmic rays.
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AA 2011/2012 Vacuum technology
M
a
s
s
S
p
e
c
t r
o
m
e
t
r
y
Partial pressure measurementsPartial pressure measurementsPartial pressure measurementsPartial pressure measurements
�An electron beam is required in order to ionized the gas in the vacuum system.
�Ion optic pieces in order to extract the ions from the ionizing volume and focus it in the filtering system.
AA 2011/2012 Vacuum technologyAA 2011/2012 Vacuum technology
Ion sourceIon sourceIon sourceIon source
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AA 2011/2012 Vacuum technology
Ion sourceIon sourceIon sourceIon source
At 70 eV max σιonization
�Dynamic or static :
the second member of the ion motion equation is function of time or not.
Ion Ion Ion Ion seperationseperationseperationseperation ((((fileringfileringfileringfilering m (m (m (m (amuamuamuamu)/q(e)))/q(e)))/q(e)))/q(e))
AA 2011/2012 Vacuum technology
),(),(),(2
2
tttdt
d
e
mrBrvrE
r ∧+=
Dynamic E(r,t) quadrupole Static B( r ) sector
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AA 2011/2012 Vacuum technology
Most frequently used in vacuum, compact and easyMost frequently used in vacuum, compact and easyMost frequently used in vacuum, compact and easyMost frequently used in vacuum, compact and easy
where
By By By By sostitutionsostitutionsostitutionsostitution: Mathieu: Mathieu: Mathieu: Mathieu----type equationtype equationtype equationtype equation
AA 2011/2012 Vacuum technology
+ for x
- for y
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� In the stability vertex: q = 0.706 we have:
where m in amu, ro in m, V in V and f = ω/2π in Hz,
and
only a given ratio m/e is stable (stay on the axis of the quadrupole spectrometer).
AA 2011/2012 Vacuum technology
),/(108.13 20
26 rfVm ⋅=
q
a
V
U
2
1=
Vacuum technology
Phenomenological Phenomenological Phenomenological Phenomenological descriptiondescriptiondescriptiondescription ((((LeyboldLeyboldLeyboldLeybold manualmanualmanualmanual) ) ) )
U constant
Adding Vcos( ωt)
givenM, i+ on the axis id f(V)
GivenU/V, i+ f(M)
II condition in whichIons are on axis for xzand yz
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�By the electron excitation of molecule we have also fragmantation effects:
FragmentationFragmentationFragmentationFragmentation----crackingcrackingcrackingcracking
AA 2011/2012 Vacuum technology
Fragmentation-cracking pattern for H2O
AA 2011/2012 Vacuum technology
Cracking pattern and isotopesCracking pattern and isotopesCracking pattern and isotopesCracking pattern and isotopes
Isotopic abundanceIsotopic abundanceIsotopic abundanceIsotopic abundance
xxx/yyy:xxx M(amu),
yyy: relative abundance.Max is 100
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AA 2011/2012 Vacuum technology
Mass Spectra parent and sonsMass Spectra parent and sonsMass Spectra parent and sonsMass Spectra parent and sons
Air mass spectrumAir mass spectrumAir mass spectrumAir mass spectrum
AA 2011/2012 Vacuum technology
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Ion Detection Ion Detection Ion Detection Ion Detection
AA 2011/2012 Vacuum technology
a) Faraday Cup
and
b) Secondary Electron Multiplier
AA 2011/2012 Vacuum technology
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AA 2011/2012 Vacuum technology
ion
Or in other words, sensitivity of Or in other words, sensitivity of Or in other words, sensitivity of Or in other words, sensitivity of
detection detection detection detection
Vacuum technology
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AA 2011/2012 Vacuum technology
Leak detectionLeak detectionLeak detectionLeak detection
Vacuum technology
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Leak detectionLeak detectionLeak detectionLeak detection
(vacuum method)(vacuum method)(vacuum method)(vacuum method)
Vacuum technology
He
Mass spectrometer usuallyB static tuned to He+
Vacuum technology
Leak check without the leak detectorLeak check without the leak detectorLeak check without the leak detectorLeak check without the leak detector