To move a particle in a (straight) line over a large distance

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1 To move a particle in a (straight) line over a large distance
Why is a Vacuum Needed? To move a particle in a (straight) line over a large distance

2 Why is a Vacuum Needed? To provide a clean surface Atmosphere
(High)Vacuum Contamination (usually water) Clean surface To provide a clean surface

3 Tabella 1a: La pressione in alcune tipiche applicazioni
Pressione Numero molecole/cm3 un pacco di caffè imballato sotto vuoto Pa 2.7 x 1018 un tubo catodico in un televisore Pa 2.7 x 1010 un acceleratore di particelle in fisica nucleare Pa 2.7 x 106 una camera con il miglior vuoto che attualmente si può produrre in laboratorio Pa 2.7 x 102 nostra galassia Pa 1-10 spazio intergalattico ? 1 al m3 Tabella 1a: La pressione in alcune tipiche applicazioni Altitudine Pressione Al livello del mare Pa Sulla vetta del Monte Bianco Pa Alla quota di crociera di un Jumbo-Jet (20000 m) Pa Su un satellite artificiale alla quota di km 2 x 10-3 Pa Sulla superficie della luna x 10-5 Pa Tabella 1b: Cambiamento della pressione in funzione dell’altitudine

4 HOW DO WE CREATE A VACUUM?

5 VACUUM PUMPING METHODS
Sliding Vane Rotary Pump Molecular Drag Pump Turbomolecular Pump Fluid Entrainment VACUUM PUMPS (METHODS) Reciprocating Displacement Pump Gas Transfer Vacuum Pump Drag Entrapment Positive Displacement Kinetic Rotary Diaphragm Piston Liquid Ring Piston Pump Plunger Pump Roots Multiple Vane Dry Adsorption Cryopump Getter Getter Ion Sputter Ion Evaporation Ion Pump Bulk Getter Cold Trap Ion Transfer Gaseous Ring Pump Turbine Axial Flow Radial Flow Ejector Liquid Jet Gas Jet Vapor Jet Diffusion Ejector Pump Self Purifying Diffusion Pump Fractionating Condenser Sublimation

6 BAROMETER 10.321 mm 760 mm 29,9 in WATER MERCURY
Mercury: times heavier than water: Column is x shorter : 10321 mm/13.58=760 mm (= 760 Torr) 10.321 mm 760 mm 29,9 in WATER MERCURY (Page 12 manual)

7 AT SEA LEVEL, 0O C AND 45O LATITUDE
PRESSURE OF 1 STANDARD ATMOSPHERE: 760 TORR, 1013 mbar AT SEA LEVEL, 0O C AND 45O LATITUDE

8 Atmospheric Pressure (Standard) =
Pressure Equivalents Atmospheric Pressure (Standard) = 14.7 29.9 760 760,000 101,325 1.013 1013 gauge pressure (psig) pounds per square inch (psia) inches of mercury millimeter of mercury torr millitorr or microns pascal bar millibar

9 THE ATMOSPHERE IS A MIXTURE OF GASES
PARTIAL PRESSURES OF GASES CORRESPOND TO THEIR RELATIVE VOLUMES GAS SYMBOL PERCENT BY VOLUME PARTIAL PRESSURE TORR PASCAL Nitrogen Oxygen Argon Carbon Dioxide Neon Helium Krypton Hydrogen Xenon Water N2 O2 A CO2 Ne He Kr H2 X H2O 78 21 0.93 0.03 0.0018 0.0005 0.0001 Variable 593 158 7.1 0.25 1.4 x 10-2 4.0 x 10-3 8.7 x 10-4 4.0 x 10-4 6.6 x 10-5 5 to 50 79,000 21,000 940 33 1.8 5.3 x 10-1 1.1 x 10-1 5.1 x 10-2 8.7 x 10-3 665 to 6650 (Page 13 manual)

10 VAPOR PRESSURE OF WATER AT VARIOUS TEMPERATURES
T (O C) 100 25 -40 -78.5 -196 P (mbar) 1013 32 6.4 0.13 6.6 x 10 -4 10 -24 (BOILING) (FREEZING) (DRY ICE) (LIQUID NITROGEN) (Page 14 manual)

11 (Page 15 manual)

12 Vapor Pressure of some Solids
(Page 15 manual)

13 PRESSURE RANGES RANGE ROUGH (LOW) VACUUM HIGH VACUUM ULTRA HIGH VACUUM
759 TO 1 x (mbar) 1 x TO 1 x (mbar) LESS THAN 1 x (mbar) (Page 17 manual)

14 Viscous and Molecular Flow
Viscous Flow (momentum transfer between molecules) Molecular Flow (molecules move independently)

15 FLOW REGIMES Viscous Flow:
Distance between molecules is small; collisions between molecules dominate; flow through momentum transfer; generally P greater than 0.1 mbar Transition Flow: Region between viscous and molecular flow Molecular Flow: Distance between molecules is large; collisions between molecules and wall dominate; flow through random motion; generally P smaller than 10 mbar -3 (Page 25 manual)

16 MOLECULAR DENSITY AND MEAN FREE PATH
Il libero cammino medio è inversamente proporzionale alla pressione ed alla sezione d’urto della molecola di gas MOLECULAR DENSITY AND MEAN FREE PATH 1013 mbar (atm) 1 x mbar 1 x mbar # mol/cm3 MFP 3 x (30 million trillion) 4 x (40 trillion) 4 x 10 7 (40 million) 2.5 x in 6.4 x mm 2 inches 5.1 cm 31 miles 50 km

17 Portata: Conduttanza: P1 A’ A Flusso P2 P1 > P2
Q è costante lungo il tubo e pertanto Conduttanza:

18 Conduttanza in parallelo:
Conduttanza in serie: C1 C2 C1 Q1 P2 P3 P1 P1 P2 Q C2 Q2 Flusso costante: Flusso totale = somma dei flussi

19 VELOCITA’ DI POMPAGGIO DI UNA POMPA
Ppompa PCamera C Camera Q Pompa VELOCITA’ EFFETTIVA DI POMPAGGIO DI UN SISTEMA: L’effetto della conduttanza è quello di ridurre la velocità di pompaggio efficace Rispetto alla velocità di pompaggio all’imbocco della pompa

20 FLOW REGIMES Mean Free Path Characteristic Dimension Viscous Flow:
is less than 0.01 Mean Free Path Characteristic Dimension Transition Flow: is between 0.01 and 1 Mean Free Path Characteristic Dimension Molecular Flow: is greater than 1

21 Conductance in Viscous Flow
Under viscous flow conditions doubling the pipe diameter increases the conductance sixteen times. The conductance is INVERSELY related to the pipe length d = diameter of tube in cm l = length of tube in cm P1 = inlet pressure in torr P2 = exit pressure in torr EXAMPLE: d = 4 cm P1 = 2 torr l = 100 cm P2 = 1 torr C=530 l/s (Page 28 manual)

22 Conductance in Molecular Flow
Under molecular flow conditions doubling the pipe diameter increases the conductance eight times. The conductance is INVERSELY related to the pipe length. d = diameter of tube in cm l = length of tube in cm T = temperature (K) M = A.M.U. EXAMPLE: T = 295 K (22 OC) d = 4 cm M = 28 (nitrogen) l = 100 cm C=7.9 l/s

23

24 GAS LOAD (Q) IS EXPRESSED IN:
Permeation Outgassing Real Leaks Diffusion Virtual Backstreaming GAS LOAD (Q) IS EXPRESSED IN: mbar liters per second

25 Pumpdown Curve 10+1 10-1 Volume 10-3 10-5 Pressure (mbar)
Surface Desorption 10-7 Diffusion 10-9 Permeation 10-11 10 1 10 3 10 5 10 7 10 9 10 11 10 13 10 15 10 17 Time (sec)

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