2. Ultra-high vacuum techniques and chamber (UHV) – Part 1
Luca Petaccia
Elettra Sincrotrone Trieste, Italy
October 2018
Institute for Research in Fundamental Sciences (IPM)
Niavaran sq., Tehran, Iran

3. Elettra Sincrotrone Trieste
400 employees m2
5000 hours/year
34 beamlines
more than 1000 Users
from more than 50 countries
Elettra is the third generation storage ring (2 and 2.4 GeV ) that has been in operation since October Since 2010 Elettra operates in the top up mode for both 2 and 2.4 GeV operational energy.
FERMI is the new seeded free electron laser (FEL) facility under commissioning next to Elettra. It is unique among the only five FEL sources currently operating in the ultraviolet and soft x-ray range worldwide since it is the first seeded FEL. FERMI is now performing its first experiments with users. It integrates Elettra performances in the (10-100) femtoseconds range.
FEL-1: Wavelength nm Photon energy 12 – 62 eV open to users
FEL-2: Wavelength nm Photon energy eV in commissioning + =
Elettra
3º generation
Synchrotron
Radiation
Source
2.0 & 2.4 GeV
FERMI
Seeded
Free
Electron
Laser
7-70 nm

5. BaDElPh: Band Dispersion and Electron-Phonon coupling beamline
Elettra synchrotron:
2.0 GeV mA
2.4 GeV mA
in top-up mode
BaDElPh at a glance…

6. Why know about UHV techniques and chamber ?
Aims:
What you ought to know about using vacuum
What you might need
A quick starter for using vacuum equipment
Cover entire range of vacuum, not just UHV

7. Contents Levels of vacuum and subsequent applications
Gas flow modelling
Vacuum pumps
Pump configurations
Pressure measurements: From atmosphere to UHV
Chambers, fittings, and materials
Complete systems
Reaching the ultimate pressure
Basics
Achieving Vacuum

8. Contents Levels of vacuum and subsequent applications
Gas flow modelling
Vacuum pumps
Pump configurations
Pressure measurements: From atmosphere to UHV
Chambers, fittings, and materials
Complete systems
Reaching the ultimate pressure
Basics
Achieving Vacuum

9. Resources Other References:
“Basic Vacuum Technology”, A. Chambers, R.K. Fitch and B.S. Halliday
“Handbook of Vacuum Technology”, K. Jousten ed.
Vacuum equipment manufacturers:
Catalogues, websites, e.g. Edwards, Varian, Pfeiffer Vacuum, Alcatel, etc.

10. Defining Vacuum
Ideal
A space containing nothing, i.e. totally devoid of all matter
Does not exist, even in outer space!
Real
A space containing gas at any subatmospheric pressure P
Practical
Any volume which has fewer gas molecules than the same size volume in the surrounding atmosphere or atmospheric pressure
P < 760 sea level and 0C with no humidity
What is a vacuum?
Pressure (symbol: p or P) is the Force (F) applied perpendicular to the surface of an object per unit Area (A) over which that force is distributed.
Without bothering Democritus, Aristoteles, Pascal, Torricelli et al… a modern definition of “vacuum” is the following (American Vacuum Society, 1958):
“… given space or volume filled with gas at pressures below atmospheric pressure”

11. PARTIAL PRESSURES OF GASES CORRESPOND TO THEIR RELATIVE VOLUMES
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 Ar
CO2 Ne He Kr H2 Xe
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
Dalton’s law: the total pressure exerted is equal to the sum of the partial pressures of the individual gases
(in a mixture of non-reacting gases).

12. Torricelli Experiment: Barometer
1 (standard) atmospheric pressure:
760 mmHg = 760 Torr
@ sea level and 0C with no humidity
vacuum
Mercury is x heavier than Water:
H2O-column is x longer than Hg-column:
760 mmHg (= 760 Torr) x = mmH2O
760 mm
10.321 mm
Only in the 17th century were vacuum physics and technology born. [Galileo ( ) was
among the first to conduct experiments attempting to measure forces required to produce vacuum with a piston in a cylinder.] Torricelli ( ), an associate of Galileo´s, succeeded in 1644 to produce vacuum experimentally by submerging a glass tube, which was filled with mercury and closed at one end, with its open end in a pool of mercury. By using mercury instead of water, he was able to reduce the size of the apparatus to convenient dimensions. He demonstrated that the mercury column was always 760 mm above the level in the pool, regardless of size, length, shape or degree of tilt of the tube (see Fig. 1) and, in this way, he measured for the first time the pressure of atmospheric air.
MERCURY
WATER

13. Historical Perspective
1644
1657
1900
1950’s
2000+
Torricelli vacuum experiment
Manufacture of light bulbs
Ultra
High
Vacuum
Magdeburg
hemispheres
experiment
Hydrocarbon
sealed pump
Suface treatment
research to achieve XHV
Only in the 17° century were vacuum physics and technology born.
Galielo ( ), Torricelli ( ) succeeded in 1644 to produce vacuum experimentally by summerging a glass tube, which was filled with mercury and closed at one end, with its open end in a pool of mercury.
Then, Pascal ( ) and Otto von Guericke ( ), mayor of the city of Magdeburg, modified the water pump, invented the manometer, constrcuted the first air pump (1650) and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been evacuated.

14. Some Definitions Pressure: Units: Levels of Vacuum:
is the force (F) applied perpendicular to the surface of an object per unit area (A) over which that force is distributed, P = F / A
Units:
Usually used is mbar (although Pa is SI, sometime Torr)
mbar = 1 atm = Pa = 760 mmHg = 760 Torr
Levels of Vacuum:
Low Vacuum (LV): mbar
Medium Vacuum (MV): mbar
High Vacuum (HV): mbar
Ultra High Vacuum (UHV): mbar
eXtreme High Vacuum (XHV): < mbar

15. Some Equipments Ultra High Vacuum (~10-10 mbar)
Rough Vacuum (~10-1 mbar)
Rotary pump
Vacuum dessicator (glass)
UHV chamber (stainless steel) with multiple ports/flages

16. Some Applications Low Vacuum mechanichal handling
vacuum cleaner (~700 mbar)
Medium Vacuum
industrial processes
vacuum drying/packaging
incandescent light bulb (~10-2 mbar)
thermos bottle (~10-3 mbar)
High Vacuum (HV)
e-beams (welding, TV)
vacuum evaporation or coating
near earth outer space (~10-6 mbar)
Ultra High Vacuum (UHV)
keeping surfaces clean for hours (surface science, epitaxial growth)
space simulation (~10-10 mbar at 1000 km)
achieving ultra high purities (e.g. for fusion)
pressure on the moon (~10-11 mbar)
eXtreme High Vacuum (XHV)
storage rings
ultra pure growth
interstellar space (~10-17 mbar)

17. To move a particle in a (straight) line over a large distance
Why do we need vacuum?
To move a particle in a (straight) line over a large distance
i.e., to extend (and maintain) particle Mean-Free-Paths
Why do we need vacuum in science and technology?

18. To obtain (and maintain) clean surfaces
Why do we need (ultra-high) vacuum?
Atmosphere
(Ultra High) Vacuum
Contamination
(usually water)
Clean surface
Vacuum Technology’s Key Role in Surface and Materials Science.
To obtain (and maintain) clean surfaces

19. Vacuum Properties  𝑣 = 8 𝑘𝑇 𝜋 𝑚 𝜆= 1 2 𝜋 𝑑 2 𝑛 = 66 𝑃 𝑚𝑏𝑎𝑟 𝜇𝑚
PUMP
VACUUM
CHAMBER
(GAS)
Kinetic gas theory: reasonably valid
 Maxwell Boltzman Distribution
mean velocity
𝑣 = 8 𝑘𝑇 𝜋 𝑚
 Mean Free Path
𝜆= 𝜋 𝑑 2 𝑛 = 66 𝑃 𝑚𝑏𝑎𝑟 𝜇𝑚
For air-N2 (M=28) at 295 K
P (mbar) n
(litre-1)  J
(cm-2s-1)
tML
(s)
1000
2.5x1022
66 nm
2.9x1023
2.5x10-9 1
2.5x1019
66 m
2.9x1020
2.5x10-6
10-3
2.5x1016
66 mm
2.9x1017
2.5x10-3
10-6
2.5x1013
66 m
2.9x1014
2.5
10-10
2.5x109
660 km
2.9x1010
2.5x104
 Impingement Rate
Considering a vacuum system…
m = molecular mass in Kg
M = molecular mass in units of atomic mass constant
d = molecular diameter
n = molecular density, number of molecules per unit volume
A ML formation time of 2.5x10^4 s corresponds to about 7 hours.
𝐽= 𝑛 𝑣 4 = 2.63× 𝑃 𝑚𝑏𝑎𝑟 𝑀𝑇 𝑐𝑚 −2 𝑠 −1
 Monolayer formation time
𝑡 𝑀𝐿 = 1 𝐽 𝑑 2 = 2.5 ×10 −6 𝑃 𝑚𝑏𝑎𝑟 𝑠

20. Elementary Gas Transport
 Mass flow rate Q
called also throughput
quantity of gas (the volume of gas at a given pressure) passing through a plane per second at a specific T
same throughout the circuit (conservation of mass)
𝑄=𝑃 𝑑𝑉 𝑑𝑡
 Volumetric flow rate S
called also pumping speed
units are volume per unit time, e.g. l/s
number of molecules depends on P
different throughout the circuit
 Conductance C
represents the ability of a gas to flow from a pressure gradient (geometric property)
C, S same units but not the same quantity
𝑆= 𝑑𝑉 𝑑𝑡 = 𝑄 𝑃
𝐶= 𝑄 𝑃 2 − 𝑃 1

21. Types of Gas Flow Regimes
Viscous or Continuous flow in LV:
distance between molecules is small; collision between molecules dominate; flow through momentum transfer between molecules.
Fluid flow is described by the
Reynolds number and the
Knudsen number
(both dimensionless)
Laminar flow if Re < 1200
for round pipes
𝑅𝑒= 𝜌𝑣𝐷 𝜂
 = gas density
v = stream velocity
D = pipe diameter
 = m.f.p.
 = gas viscosity
𝐾𝑛= 𝜆 𝐷
Turbulent flow if Re > 3000
HV / UHV: Molecular flow if Kn > 0.5
distance between molecules is large; collision between molecules and walls dominate; flow through random motion.
MV: Transition flow if < Kn < 0.5
LV: Viscous flow if Kn < 0.01
In viscous flow, also known as continuous flow, there are frequent collisions between gas molecules, but less frequently with the walls of the vessel. In this case, the mean free path of the gas molecules is significantly shorter than the dimensions of the flow channel.
In the case of viscous flow, a distinction is made between laminar and turbulent flow. In laminar, or layered, flow the gas particles remain in the same displaced layers that are constantly parallel to each other. If the flow velocity increases, these layers are broken up and the fluid particles run into each other in a completely disordered way. This is termed turbulent flow. The boundary between these two areas of viscous flow can be expressed by the Reynolds number:

22. Types of Gas Flow Regimes
For vacuum systems:
Turbulent flow only at very high P and pumping speeds (e.g. during initial evacuation, if unthrottled)
Laminar and Transition flows are important at high pressure P (above 10-3 mbar)
gas can be ‘sucked out’
Molecular flow is dominant below 10-3 mbar in ‘normal’ sized chambers
gas flows through random collisions with walls
Types of gas flow regimes in vacuum technology
If unthrottled= se non strangolato/soffocato
Laminar
flow
Kn<0.01
Transition
flow
1>Kn<0.01
Molecular
flow
Kn>1

23. Molecular Flow dominant for HV and UHV and well understood
particles move independently
particles flow in all directions to reach dynamical equilibrium
pumps ‘wait and catch’ gas particles – high vacuum pumps
do not ‘suck’
Knudsen’s cosine law: states that the probability of a gas molecule leaving a solid surface in a given direction within a solid angle dω is proportional to cosθdω, where θ is the angle between the direction and the normal to the surface.
Particles scattered from a surface with cosine distribution to surface normal (Knudsen’s cosine law)

24. Molecular Conductance of an Aperture
Net flow through an aperture corresponds to the rate of impingement from both sides:
𝑄=𝑘𝑇 𝐽 1 − 𝐽 2 𝐴
= 𝑘𝑇 2𝜋𝑚 𝑃 1 − 𝑃 2 𝐴≡ 𝐶 0 ( 𝑃 1 − 𝑃 2 )
𝐶 0 = 𝑘𝑇 2𝜋𝑚 𝐴
C0 [l/s] = 11.8 A [cm2] for nitrogen (air) at room temperature
conductance depends on gas type and temperature as (T/m)1/2

25. Conductance of Pipes 𝐶 𝑆 = 𝐶 0 × 𝐶 𝐿 𝐶 0 + 𝐶 𝐿 𝐶 𝐿 = 𝐷 3 6𝐿 𝑘𝑇 2𝜋𝑚
Various methods for calculating conductance of pipes give same results (see O’Hanlon for details)
For short pipes (L<D) is convenient to reciprocally add the conductance for a long pipe and equivalent aperture:
For long pipes (L>>D):
𝐶 𝑆 = 𝐶 0 × 𝐶 𝐿 𝐶 0 + 𝐶 𝐿
𝐶 𝐿 = 𝐷 3 6𝐿 𝑘𝑇 2𝜋𝑚
𝐶 𝑆 = 𝐷 3 /𝐿 1+4𝐷/3𝐿
[l/s]
𝐶 𝐿 =12.4 𝐷 3 /𝐿
[l/s]
(D, L in cm) for nitrogen (air) at room temperature.
D = diameter
L = lenght
(D, L in cm) for nitrogen (air) at room temperature.
For large D, short L  large C
Accurate to about 10%

26. Conductance of Pipes: examples
Calculate the conductance of pipes with diameter D of 5 or 10 cm and lenght L of 10 or 100 cm and compare the results.
𝐶 𝑆 = 𝐷 3 /𝐿 1+4𝐷/3𝐿
[l/s]
For long pipes (L>>D):
𝐶 𝐿 =12.4 𝐷 3 /𝐿
[l/s]
(D, L in cm) for nitrogen (air) at room temperature
Results:
D= 5 cm L= 10 cm  C  90 l/s
D= 5 cm L= 100 cm  C  15 l/s
D= 10 cm L= 10 cm  C  520 l/s
D= 10 cm L= 100 cm  C  120 l/s

27. Combining Conductances
For conductances in series,
add reciprocally:
For conductances in parallel,
add normally:
1 𝐶 𝑇 = 1 𝐶 𝐶 𝐶 3
𝐶 𝑇 = 𝐶 1 + 𝐶 2 + 𝐶 3
this assumes the volumes are independent – need to be careful

28. Effect of Conductance on Pumping Speed
Calculating pumping speed at different locations
effective pumping speed at chamber S1 = Q/P1
but pump has a nominal p. s. SP = Q/P0
Q is constant (conservation of mass)
Q = (P1 - P0)Ct , from which
1 𝑆 1 = 1 𝑆 𝑃 𝐶 𝑡
Sp = nominal pump speed
The molecular conductance at the entrance aperture determines maximum speed of any pump SP

29. Viscous and Transition Flow
higher pressures in pipes to mechanical pumps mean transition and viscous flow may be important
conductance increases with pressure
important in connections to mechanical pumps
can use smaller connections
accurate calculations complex
results tabulated - often in mfr's catalogues
𝟏𝟖𝟔 𝑷𝑫 𝟒 /𝑳
𝟏𝟐.𝟒 𝑫 𝟑 /𝑳
Viscous
Flow
Transition Flow
Molecular Flow
1 Torr = mbar
Average pressure = (inlet + outlet pressure)/2
Example for a 100 cm long tube with 5 cm in diameter:
in viscous flow, at 1 mbar, C 1000 l/s
in molecular flow, at 10-3 mbar, C 10 l/s

30. The Vacuum Environment
All vacuum chambers have gas sources
All pumps have some backstreaming
Outgassing
Leaks
Virtual
Real
Backstreaming
Diffusion
Permeation
Evaporation
Sample
Outgassing: gradual loss of particles adsorbed on walls, water is the major problem.
Real leak: a fine passageway to the air outside.
Virtual leak: a small trapped volume which acts like a real leak, but it will deplete with time.
Backstreaming: a real pump removes molecules but gives some gases back.
Evaporation: liquids and greases will limit the vacuum until evaporated.
Clean components and wear gloves !
After the initial pumpdown
–all real vacuum chambers have gas sources such as outgassing andinleakage
–all real pumps have some backflow
𝑄 𝑇 = 𝑄 𝑠 + 𝑄 𝑂 + 𝑄 𝐿 + 𝑄 𝑉𝐿 + 𝑄 𝐸 + 𝑄 𝐵 + 𝑄 𝐷 + 𝑄 𝑃

31. Pumpdown 𝑉 𝑑𝑃 𝑑𝑡 = 𝑄 𝑇 −𝑆𝑃 𝑃= 𝑃 0 𝑒 − 𝑆 𝑉 𝑡 𝑃= 𝑄 𝑇 𝑆
Mass balance equation (fixed V)
i.e., gas change in the chamber is ‘gas load’ minus gas removed by pump
Solving fully requires detailed knowledge of Q not generally available
– evaporation and outgassing of different gases gives complex behavior…
For initial air pumpdown - volume gas only (QT not important)
𝑉 𝑑𝑃 𝑑𝑡 = 𝑄 𝑇 −𝑆𝑃
𝑃= 𝑃 0 𝑒 − 𝑆 𝑉 𝑡
Constant volume system governed by…
Eq. means: gas change in the chamber is ‘load gas Q’ minus gas removed by pump
Later on - desorbed gas, and at ‘equilibrium’ (dP/dt not important)
𝑃= 𝑄 𝑇 𝑆

32. Pumpdown: example in LV
Mass balance equation (fixed V)
For initial air pumpdown, in LV - QT not important:
𝑉 𝑑𝑃 𝑑𝑡 = 𝑄 𝑇 −𝑆𝑃
𝑃= 𝑃 0 𝑒 − 𝑆 𝑉 𝑡
𝑆= 𝑄𝑇 𝑃 − 𝑉 𝑃 𝑑𝑃 𝑑𝑡
𝑆 𝑡2−𝑡1 =𝑉 𝑙𝑛 𝑃1 𝑃2
Example:
Chamber with V = 800 l = 0.8 m3
Pump (primary) with S = 40 m3/h
Determine the evacuation time from atmosphere to 10-1 mbar ?
Mass balance equation (fixed V), i.e., gas change in the chamber is ‘gas load’ minus gas removed by pump
𝑡2−𝑡1 = 𝑙𝑛 =0.18 ℎ=11 𝑚𝑖𝑛

33. Pumpdown: example in HV / UHV
Mass balance equation (fixed V)
Later on, in HV/UHV - desorbed gas, and at ‘equilibrium’ (dP/dt not important)
𝑉 𝑑𝑃 𝑑𝑡 = 𝑄 𝑇 −𝑆𝑃
𝑃= 𝑄 𝑇 𝑆
Example:
Cylindrical chamber in SS AISI 304L (=1m, L=1m, outgassing rate Dss=5×10-9 torr l/s cm2)
connected to a Turbo pump through a pipe (=20cm, L=10cm) and a valve (C2=8000 l/s, Dviton=10-7 torr l/s cm2, Aviton=2 cm2), other materials provide “gas load” of 10-9 torr l/s.
Determine the Sp of the Turbo pump in order to reach an equilibrium P=3×10-7 torr ?
𝑄𝑇= 𝑄𝑆𝑆 + 𝑄𝑣𝑖𝑡𝑜𝑛 + 𝑄𝑅= 𝑖 𝐴𝑖𝐷𝑖=
𝐴 𝐶ℎ =47300 cm2
= 48000×5× × = 2.4×10-4 torr l/s
Mass balance equation (fixed V), i.e., gas change in the chamber is ‘gas load’ minus gas removed by pump
D = outgassing rate of the material in (mbar l/s cm^2)
Q = DxA where A is the surface area of the material.
Chamber Area 2 basi: 2 x 50^2 x pi = cm2
Chamber Area laterale: 2 x 50 x pi x 100 = cm2
Pipe Area: 2 x 10 x pi x 10 = 628 cm2
Quindi Area totale in SS: cio’ circa 4.8x104
𝑆1= 𝑄 𝑇 𝑃 =2.4× 10 − ×10 −7 =800 𝑙/𝑠
1 𝑆 𝑛𝑜𝑚  1 𝑆 𝑃 = 1 𝑆 1 − 1 𝐶 𝑡 = − −
𝐶 1 = 𝐷 3 /𝐿 1+4𝐷/3𝐿 =2700 l/s
𝐴 1 =700 cm2
𝐶 2 =8000 l/s
𝑆𝑃 ≅1300 𝑙/𝑠

34. Pumpdown Curve (𝑒 −𝑘𝑡 ) ( 1 𝑡 ) ( 1 𝑡 )
Outgassing limits vacuum in a clean, leaktight HV/UHV chamber
made up of general ‘grot’ greases, water vapour…
For UHV, must accelerate degassing of water by baking to 150C for 24 hours
desorption is activated with Boltzmann factor
rule of thumb: rate doubles for every extra 10C
can get to UHV in days instead of months/years
Ultimate pressure?
diffusion/permeation of H through chamber walls
Volume Gas
(𝑒 −𝑘𝑡 )
Outgassing
( 1 𝑡 )
Diffusion
( 1 𝑡 )
Permeation
Grot = sporcizia

35. Positive Displacement
Vacuum Generation
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
Wide variety of pumps used at all pressure levels
Concentrate on main types of pumps used in research

36. Vacuum Pumps Wide variety of pumps used at all pressure levels
Concentrate on main types of pumps used in research
All Vacuum Pumps
Gas Transfer
Entrapment
Kinetic
Positive
Displacement
Moving components displace and eject a volume of gas,
e.g. rotating vanes.
Momentum imparted to individual gas particles, driving them to exhaust,
e.g. rotor in a turbomolecular pump.
Gas particles react chemically and trapped, or ionized, accelerated, and embedded in pump walls,
e.g. getter/ion pumps.

37. Vacuum Pumps and Pressure
Viscous Flow
Molecular Flow
Pressure (mbar)
HV-UHV Pumps
Roughing Pumps
Rotary vane pump
Membrane pump
Scroll pump
others:
roots pump
piston pump …
Turbomolecular pump
Ion pump
Getter pump
others:
cryo pump …

38. Rotary Vane Pump Single stage
Standard mechanical pump, used to achieve rough vacuum
Sliding vanes rotate, compressing and ejecting gas to atmosphere
Sealed with oil
Needs replacing periodically
Needs foreline trap into inlet line to keep oil from backstreaming
Special oils available for pumpimg oxygen & aggressives – else BANG !

39. Rotary Vane Pump

40. Molecular Sieve(Zeolite) Foreline Trap
Foreline trap into inlet line to keep oil from backstreaming!
The Molecular Sieve Foreline Trap will help remove hydrocarbons, water vapor, and other gases. This helps to decrease the amount of vapor backstreaming, while increasing the life of the oil and pump.
The active material is Zeolite (Alluminosilicati)…
The porous nature of the Zeolite allows for the capture of water and oil vapor.
Time to time it has to be cleaned. Performing a bakeout (usually up to 250 C, max 315 C) will remove the water vapor, allowing for further use of the Zeolite. Once the Zeolite is fully saturated with oil, the zeolite will need to be replaced.
Zeolite needs bakeout to remove water vapor and needs to be replaced when fully saturate with oil vapor

41. Double-stage Rotary Vane Pump
Double stage rotary pump gives better ultimate pressure
Two stages in series
difficult to expel condensables
e.g. water vapour
gas ballast helps (leak air in between stages)
Typically get down to 2x10-3 mbar
Pumping speeds ~ 0.5  80 m3/hr
Cost ~1000 € for few m3/hr

42. Scroll Pump
A scrool pump is a type of roughing pump which works using the principle below
The rest gas of the recipient enters the opening between two archimedean spirals, one fixed and one rotating. Due to the rotation, the volume between the spirals is expanded and eventually sealed off and transported away. Scroll pump has the advantage of not using oil for sealing, i.e. it is a dry pump.
- pressure down to 7x10-3 mbar
- pumping speeds ~5  50 m3/hr
- cost ~3000 € for few m3/hr

43. Membrane Pump Dry pumps generally:
can avoid contamination altogether, if necessary
e.g. silicon wafer processing
several mechanisms available, e.g. diaphragm, PTFE sealed pistons
lower pumping speed
poorer ultimate pressure
relatively more expensive
- pressure down to 1 mbar
- pumping speeds ~0.3  20 m3/hr
- cost ~2000 € for few m3/hr

44. Other Mechanical Pumps
Other mechanical pumps are available, e.g.:
piston pumps
roots pump
Usually designed for high pumping speeds needed in industry

45. Getting to High Vacuum
Need different type of pump to get below about 10-3 mbar
Usually means using either:
diffusion pump
turbo pump
High vacuum pumps cannot discharge to atmospheric pressure
permanently need a rotary pump as a support or backing pump

46. (Oil) Diffusion Pump Boils highly refined, high molecular weight fluid
Baffle
Boils highly refined, high molecular weight fluid
Vapor jets impart downward momentum to gas entering pump
Oil condenses on water cooled body & recycled
Discharges to rough vacuum
‘critical backing pressure' ~0.5 mbar (depends on model)
Reliable 'standard', gets down to between ~10-7 and ~10-11 mbar depending on setup
1 Top nozzle
2 Cold cap

47. (Oil) Diffusion Pump
Ultimate pressure depends on quality of fluid used
cheap fluid (e.g. Corning DC704) ~10-6 mbar
good fluid (e.g. Edwards L9) ~ 10-9 mbar
best fluid (Santovac 5) ~10-10 mbar (with baffle)
Different fluids have different safety issues
Need chevron baffle to catch backstreaming pump fluid and achieve best pressures

48. (Oil) Diffusion Pump: Chevron Baffle
All diffussion pumps backstream pump fluid when hot
Cold, optically dense baffle catches oil, but reduces the pumping speed (~50%)
Need liquid-N2 temperature to reduce vapour pressures to UHV level
once nitrogen reservoirs filled, need to be kept filled
internal water condensation can refreeze in cracks and cause leaks

49. (Oil) Diffusion Pump Disadvantages: Advantages:
Fairly cheap (start ~ €1000)
Reliable - little to go wrong
heater is replaceable
cooling coils can be descaled
can take to bits and scrub out inside
Often found 'lying around' lab…
Disadvantages:
Low to start and stop
~½ hr to warm up
~1 hr to cool down before venting
Expensive to run large pumps (€1000s per year)
Require liquid-N2 baffles for true UHV (require daily filling!)
Dependent on cooling water – MUST BE INTERLOCKED
Descale=disincrostare
can take to bits and scrub out inside=può prendere a pezzi e strofinare dentro

50. Turbomolecular Pump
Fast moving rotors and stators impart momentum to gas molecules
Frequency up to ~1500 Hz
High precision greased/oiled or magnetic bearings

51. Turbomolecular Pump Pumping speed varies with gas and pressure
Maximum compression ratio of the Turbo pump is defined to
be the ratio of the outlet pressure to the inlet pressure and it varies with molecular mass.
Compression ratio (K0 = Pout / Pin) varies with molecular mass
typically for N2
typically ~104 for He
typically ~103 for H2

52. Turbomolecular Pump Difficult to remove lighter gases
>10-6 mbar
~10-2 mbar
1000 mbar
~10-9 mbar
Difficult to remove lighter gases
can add extra pumps in series to improve compression
add chemical pump in parallel to pump reactive species (e.g. H2)
Bake out the system to achieve UHV-XHV
p < mbar

53. Turbomolecular Pump Disadvantages: Advantages:
Quite expensive to buy and service
Occasional catastrophic failure
something dropped in top bearing seizes
magnetic controller fails
Need to be well secured (SAFETY RISK)
e.g. Leybold T1600 has to be secured to withstand an impact torque of Nm
Advantages:
Quick to start and stop
Low electrical costs
Clean – completely so for a mag-lev
Can be mounted in more orientations
Air or water cooling
Mag-lev turbos good for aggressive gases

54. Ion Pump
Type of entrapment pump, operating like a series of Penning gauges
Electrons spiral in strong magnetic field, ionizing gas species on impact
Ions are accelerated to and get buried in surface of anode
Clean pumping to UHV, but requires large magnet
Needs additional pump to get down to about 10-4 mbar before ion pump will start

55. Getter Pump
Chemical 'getter' pump, reacts with and contains reactive elements
Various types of getter
sublimated coatings (TSP uses Ti/Mo alloy)
blocks of reactive, sintered material (NEG)
Particularly good at pumping H2, unlike many other pumps
Limited capacity - has to be used at very low pressures
Cannot pump inert/rare gases
Use strip getters along entire length of particle accelerator beamlines to achieve XHV
Once activated, pumps without power - portable!

56. Cryo Pump
A cold surface condenses volatiles (water, oil, etc.) and even air particles if sufficient nooks and crannies exist
a dessicant, or getter, traps particles of gas in cold molecular-sized “caves”
Put the getter in the coldest spot
- helps guarantee this is where particles trap: don’t want condensation on critical parts
when cryogen added, getter gets cold first
Cooling via liquid-N2 (77 K, for H2O, CO2…)
or liquid-He (4 K, for permanent gases)
lower temperature, greater pumped gases
Clean pump, working in 10-4  mbar
Essentially “pumps” remaining gas, and even continued outgassing
Nooks=angoli (cavita’)
Crannies=crepe

57. Choice of Pumps Choice of pumps depends on: level of vacuum
size of chamber (outgassing)
gas throughput of process
pumpdown time
type of gas (nasty?)
level of cleanliness required
size and positioning
finances available (!) …
careful consideration and risk assessment is vital
number of big mfrs.:
never pay list price for new vacuum equipment
discounts of up to ~50% are routine for academia

58. Thank you for the attention!