PHYSICS 225, 2ND YEAR LAB - PowerPoint PPT Presentation


Title: PHYSICS 225, 2ND YEAR LAB


1
PHYSICS 225, 2ND YEAR LAB
  • VACUUM TECHNOLOGY

G.F. West
Thurs, Jan. 12
2
INTRODUCTION
  • Humans work in a gaseous environment.
  • Although less dense than solids or liquids, the
    normal gas environment greatly influences much
    physics.
  • Often, to do interesting and important physics,
    one must get rid of it.

3
WHAT IS A VACUUM ?
  • The absence of appreciable matter (i.e., atoms,
    molecules, ions, particles), usually as gas.
  • How do we measure the amount of gas?
  • As mechanical pressure on container walls or
    neighbouring gas.
  • Pressure Force /unit area N/m2 Pa (SIU)
  • bars (cgs)
  • psi (USA/Imperial)
  • Atm (Chem)
  • mmHg Torr (traditional physics)

4
KINETIC THEORY OF GASSES (The colliding
billiard ball model )
  • Gas atoms have a range of velocities, increasing
    with temperature.
  • Gas molecules therefore have appreciable energy
    and momentum.
  • Pressure is the cumulative result of the momentum
    changes in collisions.
  • Collision likelihood is usually expressed as
    mean free path (average distance molecules move
    between collisions).

5
LEVELS OF VACUUM
  • Air at 273 K, molecular Vrms 485 m/s
  • Pressure (V HV UHV UHV )
  • Atm, 1.0 1/760 - - - -
  • kPa, 101.3 0.13, 0.13Pa - - -
  • psi, 14.7 0.02 - - -
    -
  • Torr, 760 1 1e-3 1e-6 1e-9
    1e-12
  • Mean Free Path, at 273 K, mol radius 0.3 nm
  • m 1e-7,7e-5,7e-2, 7e1,7e4, 7e7

6
VACUUM PUMPS
  • Mechanical with valves, vanes, diaphrams
  • (Roughing pumps, forepumps).
  • Entrainment principle
  • Diffusion pumps,
  • Turbomolecular pumps.
  • Entrapment principle
  • Cryopumps,
  • ionpumps (gettering)
  • TI sputtering
  • molecular sieves (zeolites and other synthetic
    microporous compounds)

7
PROBLEMS WITH PUMPING
  • Need for a forepump.
  • Contamination of vacuum by backflow.
  • Gas selectivity.
  • Need for regeneration.
  • Virtual leaks.
  • Speed, ease of cycling to lab conditions.

8
VAPOUR PRESSURE
9
MULTI-PUMP SYSTEM
10
ROTARY VANE FORE PUMP
11
DIFFUSION PUMPS
12
TURBO-MOLECULAR PUMPS
13
TURBO-MOLECULARPUMP
14
ION PUMP
15
ION VACUUM GAUGE
16
THE VACUUM ENCLOSURE
  • Materials -
  • (Glass stainless steel predominate.)
  • Requirements-
  • Chemically inert
  • Cleanable
  • Bakeable
  • Strong
  • Workable, (e.g., machineable)

17
TYPICAL VACUUM SYSTEM
  • Forepump
  • Main vacuum pump with cooling.
  • Gate valve,(to allow pump turn off).
  • Vacuum gauges, if not intrinsic to pumps.
  • Cold trap(s) (Liquid air).
  • Sample inlets, if required.
  • View manipulation ports, experiment area.
  • Bakeout system.

18
VACUUM SYSTEM COMPONENTS
  • Older systems mainly were hand fabricated from
    glass by artisanal glassblowing.
  • New systems mainly are constructed from
    commercially manufactured stainless steel
    components using (e.g.,)-
  • Bolted flange connections
  • Thin metal seals
  • Glass- to-metal sealed electrical connections
  • Bellows connected or in-vac bakeable manipulators
  • Special window glasses for radiation entry/exit

19
VACUUM COMPONENTS
20
USES OF VACUUM TECHNOLOGY
Some examples-
  • Semiconductor lithography and surface coating.
  • Analytical insts e.g., spectrometers,
    microscopes.
  • Particle accelerators, HEP
  • Space simulation
  • Nanotechnoloy
  • Surface physics.
  • Gas lasers.
  • Manufacturing of special materials.
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PHYSICS 225, 2ND YEAR LAB

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Humans work in a gaseous environment. ... Gas selectivity. Need for regeneration. Virtual leaks. Speed, ease of cycling to lab conditions. ... – PowerPoint PPT presentation

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Title: PHYSICS 225, 2ND YEAR LAB


1
PHYSICS 225, 2ND YEAR LAB
  • VACUUM TECHNOLOGY

G.F. West
Thurs, Jan. 12
2
INTRODUCTION
  • Humans work in a gaseous environment.
  • Although less dense than solids or liquids, the
    normal gas environment greatly influences much
    physics.
  • Often, to do interesting and important physics,
    one must get rid of it.

3
WHAT IS A VACUUM ?
  • The absence of appreciable matter (i.e., atoms,
    molecules, ions, particles), usually as gas.
  • How do we measure the amount of gas?
  • As mechanical pressure on container walls or
    neighbouring gas.
  • Pressure Force /unit area N/m2 Pa (SIU)
  • bars (cgs)
  • psi (USA/Imperial)
  • Atm (Chem)
  • mmHg Torr (traditional physics)

4
KINETIC THEORY OF GASSES (The colliding
billiard ball model )
  • Gas atoms have a range of velocities, increasing
    with temperature.
  • Gas molecules therefore have appreciable energy
    and momentum.
  • Pressure is the cumulative result of the momentum
    changes in collisions.
  • Collision likelihood is usually expressed as
    mean free path (average distance molecules move
    between collisions).

5
LEVELS OF VACUUM
  • Air at 273 K, molecular Vrms 485 m/s
  • Pressure (V HV UHV UHV )
  • Atm, 1.0 1/760 - - - -
  • kPa, 101.3 0.13, 0.13Pa - - -
  • psi, 14.7 0.02 - - -
    -
  • Torr, 760 1 1e-3 1e-6 1e-9
    1e-12
  • Mean Free Path, at 273 K, mol radius 0.3 nm
  • m 1e-7,7e-5,7e-2, 7e1,7e4, 7e7

6
VACUUM PUMPS
  • Mechanical with valves, vanes, diaphrams
  • (Roughing pumps, forepumps).
  • Entrainment principle
  • Diffusion pumps,
  • Turbomolecular pumps.
  • Entrapment principle
  • Cryopumps,
  • ionpumps (gettering)
  • TI sputtering
  • molecular sieves (zeolites and other synthetic
    microporous compounds)

7
PROBLEMS WITH PUMPING
  • Need for a forepump.
  • Contamination of vacuum by backflow.
  • Gas selectivity.
  • Need for regeneration.
  • Virtual leaks.
  • Speed, ease of cycling to lab conditions.

8
VAPOUR PRESSURE
9
MULTI-PUMP SYSTEM
10
ROTARY VANE FORE PUMP
11
DIFFUSION PUMPS
12
TURBO-MOLECULAR PUMPS
13
TURBO-MOLECULARPUMP
14
ION PUMP
15
ION VACUUM GAUGE
16
THE VACUUM ENCLOSURE
  • Materials -
  • (Glass stainless steel predominate.)
  • Requirements-
  • Chemically inert
  • Cleanable
  • Bakeable
  • Strong
  • Workable, (e.g., machineable)

17
TYPICAL VACUUM SYSTEM
  • Forepump
  • Main vacuum pump with cooling.
  • Gate valve,(to allow pump turn off).
  • Vacuum gauges, if not intrinsic to pumps.
  • Cold trap(s) (Liquid air).
  • Sample inlets, if required.
  • View manipulation ports, experiment area.
  • Bakeout system.

18
VACUUM SYSTEM COMPONENTS
  • Older systems mainly were hand fabricated from
    glass by artisanal glassblowing.
  • New systems mainly are constructed from
    commercially manufactured stainless steel
    components using (e.g.,)-
  • Bolted flange connections
  • Thin metal seals
  • Glass- to-metal sealed electrical connections
  • Bellows connected or in-vac bakeable manipulators
  • Special window glasses for radiation entry/exit

19
VACUUM COMPONENTS
20
USES OF VACUUM TECHNOLOGY
Some examples-
  • Semiconductor lithography and surface coating.
  • Analytical insts e.g., spectrometers,
    microscopes.
  • Particle accelerators, HEP
  • Space simulation
  • Nanotechnoloy
  • Surface physics.
  • Gas lasers.
  • Manufacturing of special materials.
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