PHYSICS 225,
2ND YEAR LAB
VACUUM TECHNOLOGY
G.F. West
Thurs, Jan. 12
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.
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);
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).
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, ~7e+1,~7e+4, ~7e+7
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)
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.
VAPOUR PRESSURE
MULTI-PUMP SYSTEM
ROTARY VANE FORE PUMP
DIFFUSION PUMPS
TURBO-MOLECULAR PUMPS
TURBOMOLECULAR
PUMP
Specifications
MDP 5011
Pumping speed (L/s N2)
Ultimate pressure (Torr)
7.5
7.5 x 10
-7
Compression ratio:
9
......N2
1 x 10
......He
2 x 10
......H2
1 x 10
Speed (rpm)
27,000
Max. ambient temp (°C)
Exhaust flange
4
3
50
QF16
Pump weight (lb)
5.5
Power supply (VAC)
115
Other voltages available on request
ION PUMP
ION VACUUM GAUGE
THE VACUUM ENCLOSURE


Materials: (Glass & stainless steel predominate.)
Requirements:




Chemically inert
Cleanable
Bakeable
Strong
Workable, (e.g., machineable)
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.
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
VACUUM COMPONENTS
USES OF VACUUM TECHNOLOGY
Some examples:







Semiconductor lithography and surface coating.
Analytical inst’s; e.g., spectrometers, microscopes.
Particle accelerators, HEP
Space simulation
Nanotechnoloy
Surface physics.
Gas lasers.
Manufacturing of special materials.