Getters :
From Light Bulbs to
Accelerators
F. Le Pimpec
SLAC/NLC
PSI October 2004
A Demonstration !
Bulb Installed in 1901 at the
Livermore’s (CA) Fire station.
C filament - 4 W
Phosphorus-pumped lamps tend to
have a red color cast.
CERN : LEP/LHC aerial Picture
Vacuum insured by St101 (Zr-Al) NEG
From Ref [1]
F. Le Pimpec - SLAC
2
Importance of talking about getters ?
Luminosity
for colliders
&
Lifetime
for Storage Rings
-14
10-13 10-12 10-11 10-10 10-9
Torr 10
10-8
10-7
10-6
10-5
10-4
10-3
Vacuum Gauges
Spinning Rotor gauge
Penning gauge
Hot Cathod Ionization gauge, Bayard Alpert
Cold Cathod Discharge gauge
Extractor - Ionization gauge, Modified Bayard Alpert
Improvement
of electronic devices, the
Edison effect (thermionic
emission) 1883, to
polarized photocathodes
at the beginning of the
3rd millennium
Vacuum Pumps
Cryopump
Diffusion pump
Turbomolecular pump
Titanium Sublimation pump
Ion Sputter pump
Non Evaporable Getter pump & Cryogenic pump
F. Le Pimpec - SLAC
3
10-2
The Invention of the Light Bulb:
Davy, Swan and Edison
1800
1878
1879
Edison filed the patent
after Swan and still
made the $$$
An advertisement for xray apparatus by the
Edison Decorative and
Miniature Lamp
Department.
From an issue of the Scientific
American 1898.
Diagram of Edison’s vacuum
system for the production of
incandescent lamps (1870s).
Thomas A Edison 1878
Edison Light bulbs last longer !!
True until 1910 (invention of the W filament)
F. Le Pimpec - From
SLACRef [17]
Small Dental x-ray tube mounted
4 stand
on a "deco" looking display
Evaporable Getters – Vacuum tube – Radio valves …
Dull Emitter Receiving – Radio valves, Triodes (1905) (Thoriated Tungsten filaments)
1924-1927
Ba + Mg getter
1927-1933
P getter
A Ba getter can give a blackish coloration – Customers did not
like that in the products.
Addition of Mg gave the silvery effect – and the product became
F. Le Pimpec - SLAC
salable
Arcturus_UX201A
Mg getter in the anode – no filament
Radio Tube – can produce xrays
5
What is a Getter Material ?

A priori, any clean surfaces are
getter materials.
– Bakeout, SR or e- scrubbing…
– Clean surfaces have pumping properties

To be named getter, the material
must form tied and stable bonds with
molecules from the residual gas
F. Le Pimpec - SLAC
6
Tied Bonds and Location

Tied bonds : Chemisorption ≥ eV
– Covalent bond (sharing of the e-)
– Ionic bonds (1 e- is stolen by the most electro- elements
(Mg+O-))
– Metallic bonds

(valence electrons shared)
Loose bonds : Physisorption < eV
– Van der Waals forces (~0.4eV)
– Hydrogen bonding (Polar molecules - Chemical,
(Biology))

Stable bonds can be formed :
– At the surface : Adsorption
– In the bulk of the material : Absorption
F. Le Pimpec - SLAC
7
Getters are Capture Pumps


Cryopumps and Sputter/getter-ion pumps
are also capture pumps.
Differentiation is needed
– Physical getters (Zeolite)
– Work at LN2 temperature by trapping air gases
(including water vapor). Cheap primary dry pump.
– Recycling by warming up the zeolite
–
Chemical getters or simply : getters
– “Entertainment of the moment”
F. Le Pimpec - SLAC
8
Sputter/Getter-Ion Pumps
Getter-ion pump
[ENGINEERING] A high-vacuum pump that employs
chemically active metal layers which are continuously or intermittently deposited
on the wall of the pump, and which chemisorb active gases while inert gases are
"cleaned up" by ionizing them in an electric discharge and drawing the positive
ions to the wall, where the neutralized ions are buried by fresh deposits of metal.
Also known as sputter-ion pump ref. [3].
Developed by JPL with/for NASA
Courtesy of Varian
Diode
F. Le Pimpec - SLAC
9
How Do Getters Work ?
Whatever the getter is, the
same principle applies :
The use of a clean
surface to form
chemicals bonds
When is the getter surface saturated :
: molecules.s-1.cm-2
  3.5 10 
22
P
MT
: sticking coefficient
P : Pressure (Torr)
1ML : ~1015 molecules.cm-2
F. Le Pimpec - SLAC
10
Getter Chemistry
Dissociation of residual
gases on a surface is not
systematic
Getter + O2 → Getter-O
Getter + N2 → Getter-N
Getter + CO2 → CO + Getter-O
Getter + CO2 → Getter-C + Getter-O
Getter + CO → Getter-C + Getter-O
Getter + H2O → H + Getter-O → Getter-O + H (bulk)
Getter+ H2 → Getter + H (bulk)
Getter + Hydrocarbons, CxHy → Getter-C + H (bulk)
Getter + He, Ne, Ar, Kr, Xe (inert gases) → No reaction
From P. Danielson Ref [4]
F. Le Pimpec - SLAC
11
Getter Chemistry
t
From Ref [19]
Ef
Ei
Ef Ei
Ep
C-H : 415 kJ/mol
C-C : 348 kJ/mol
C-O : 358 kJ/mol
F. Le Pimpec - SLAC
12
Gettering Materials !
 The list of materials
– Barium
– Cesium
– Magnesium
– Columbium (Nb)
– Titanium
– Uranium
is quite long…
-
Calcium
Hafnium
Phosphorus
Tantalum
Thorium
Zirconium
 Alloy
can be created in order to
enhance some properties – H2 diffusion
–
–
–
–
Aluminium
- Cobalt
Nickel
- Vanadium
Palladium
Other materials including multi getter alloys
F. Le Pimpec - SLAC
13
Choice of Getter – Vapor Pressure
When choosing a material to be used for
a vacuum application.
1
P
One question which need to be asked is :
At Which temperature my
system is going to be running ?
Zn
Mg
10-7
50
200
1
Al
700
The elements of your vacuum system
must not limit the pressure you are
aiming at.
Their vapor pressure must be taken into
account in the design. That is also true
for your getter pump
Al
Ti
10-7
After Honig and Kramer (1969)
700
F. Le Pimpec - SLAC
Ta
1200
14
How to Use Getters ?
There are two ways :
1.
As Evaporable Getter
– Deposition of a fresh film of
material – flash evaporation
2.
As Non-Evaporable Getters
– Use of an alloy containing one or
more gettering materials
F. Le Pimpec - SLAC
15
Evaporable Getters
Deposition of a film of getter material
- This is achieved by evaporating the getter (alloy) or by
thermal or by electron heating.
- When the pumping speed is no longer adequate (saturated
film), a new layer must be evaporated (Ti SP - Ba dispenser).
- In some applications, e.g. vacuum tubes, the evaporable
getter is deposited by the bake of the system and should hold
the vacuum for the life of the device (P - Mg - Ba).
- Temperature of evaporation depends on the material in use.
- As getters are usually highly reactive to oxygen, care must be
taken. Especially if the getter is hot.
F. Le Pimpec - SLAC
16
Evaporable Getters - Magnesium

Use
–
–
–
–

Mg is one of the 1st getter used historically
Good O2 getter – But physisorb most of the
other gases
High vapor pressure precludes use in small
vacuum tubes (P~10-5 Torr at 275°C)
Mg can be used when other types of getters
with higher evaporation temperatures have
to be avoided
Precautions
–
–
–
Mg metal is highly flammable in its pure
form, especially when it is a powder
Magnesium metal quickly reacts
exothermically upon contact with air or
water and should be handled with care
Water should not be used to extinguish
magnesium fires
F. Le Pimpec - SLAC
From Ref [2]
17
Evaporable Getters - Phosphorus

Use
–
–
–

Phosphorus (white or red) has
also a high vapor pressure.
Hence, it is not used in highvacuum discharge tubes
Inexpensive and simple to
handle, it is used for high-vacuum
tubes and gas-filled lamps
Extremely efficient at gettering O2
Precautions
–
–
–
Philips MLR160 -1984
Courtesy of Philips
This is a poisonous element, 50 mg being the average fatal
dose
The white form ignites spontaneously in air
The red form is more stable, and is obtained by sunlight or
when heated in its own vapor to 250 °C. The red form
reverts to white phosphorus in some temperature ranges
and it also emits highly toxic fumes that consist of
phosphorus oxides when it is heated.
F. Le Pimpec - SLAC
18
Evaporable Getters - Barium

Use
–
Ba was and still is one of the most
used flash getters for (high)
vacuum tubes (CRT tubes -TV) and
lamps. Ba flash getters are mainly
evaporated from alloys Ba-Al (Ba
43, Mg 20, Al 37 : KemetTM)
–

Very efficient pumping for O2 – N2
– CO2, and good for H2 and CO
Ba flash getters for glass bulbs (upper
row) and getter strip assemblies (1950)
Precautions
–
–
Ba and P are so reactive to air that you cannot find them in their
pure form. To remain pure, Ba should be kept under a petroleumbased fluid (kerosene) or other oxygen-free liquids, or produced
and kept under vacuum/inert atmosphere.
All water or acid soluble Ba compounds are extremely poisonous.
F. Le Pimpec - SLAC
19
Evaporable Getters - Titanium

Use & Limitation
– One of the new comers
–
–
–
The pumping speed of a freshly
evaporated film (from Ti filaments
or Ti-balls), can be enhanced by
cooling down the coated vessel.
Allows physisorption of CH4 (77K)
After several uses, the Ti film can
peel off. Peeling starts ~ 50m .
The film thickness depends on the
time of the sublimation and the
rate of evaporation of the Ti
For mechanical strength at
sublimation T, the Ti filament has
to be alloyed (Mo) or formed onto a
rigid structure (W or Ta)
♦ Precaution
− This is a safe product
F. Le Pimpec - SLAC
Photo courtesy of Thermionics Laboratory, Inc
Varian, Inc
20
Titanium vs. Other Getters For
Accelerator Use
Ba - Ca - Mg : High vapor pressure. Trouble if bake out is requested
Zr - Nb - Ta : Evaporation temperature too high
Typical required sublimation rate
0.1 to 0.5 g/hr
1cm2
Ref. “Le Normand CERN vacuum note”
Ref. “Sorption of Nitrogen by Titanium Films,” Harra and
Hayward, Proc. Int. Symp. On Residual Gases in Electron
Tubes, 1967
 Wide variations due to film roughness
 For H2, competition between desorption and
diffusion inside the deposited layers
F. Le Pimpec - SLAC
21
Evaporable Getters :
Generalities
- Designers must pay
attention to accidental
coating over insulators by
the evaporated film
- Poisoning by the getter,
limitation of the life time of
cathodes (polarizable esources) or filaments (W-Th)
For Accelerators Ti SP :
- Large pumping speed and capacity  Low pressure
- Inexpensive and easily operated
- No noble gas or methane pumping, methane production ???
- localized pumping (conductance limitation on their
22
F. Le Pimpec - SLAC
effectiveness)
1950
Non-Evaporable Getters
NEGs are pure metals or are alloys
of several metals
CO, N2, CO2, O2
- Unlike evaporable getters, pumping
speed of the surface is not restored by
depositing a new layer.
H2
NEG
- Restoration is achieved by “activation” heating of the substrate on which the
getter is deposited. Joule or bake heating
CO, N2, CO2, O2
- During activation, atoms migrate from
the surface into the bulk, except H2.
NEG
H2
- Heating to “very high” temperature will
outgas the getter. This regenerates it but
also damages the crystal structure.
F. Le Pimpec - SLAC
23
Some Alternative Getters

Depleted Uranium
–
–
–

Thorium
–
–
–
–

Tantalum
–
–
–
–

Very good getter (UO3)
Slightly radioactive and very pyrophoric (CERN Accident January 1999, HEP target)
Still used in some laboratories around the world. Even in custom ion pumps,
instead of Ti
Used during WW II for the production of vacuum tubes
Ceto getters (alloy) : 20% mischmetal, (Ce and other rare earth) and 80% Th
- Low Secondary Electron Yield, when compared to Ba
Pumps well at 300°C, but highly pyrophoric
Used for UHV gauges filaments (Th-Ir) (W-Th filaments used since post-WW I)
Used for sorbing noble gases (100 times its own volume), but need high
temperature degassing > 1600°C : Noble gas ion pumps
No H2 firing, because of embrittlement
In vacuum furnace, used to capture O2 and H2
Also used to getter the contaminants outgassed by Nb or Ti during heat
treatment of those materials
Titanium & Zirconium
–
Basic elements in the making of NEG of today
F. Le Pimpec - SLAC
24
Non-Evaporable Getters : Uses
St 707 (ZrVFe)
Pump cartridge for Ion Pump or as lump pumps
Application of NEG are rather wide :
NEG is used in UHV (accelerators - tokamak)
Use of St 2002 pills to insure
a vacuum of 10-3 Torr
Used for purifying gases (noble gas)
Used for hydrogen storage, including isotopes (near
embrittlement regime)
Lamps and vacuum tubes
…
F. Le Pimpec - SLAC
25
NEG & Accelerators
Cf. Benvenutti
Lump pumping
LEP dipole chamber, getter St101 (ZrAl)
(1989-2000)
~24 km of NEG  P~10-12 Torr range
Inserted “linear” pump
The LEP : 1st
major success
of intensive use
of NEG pumps
Thin film getter
is the new
adopted way of
insuring UHV in
colliders or SR
light sources
DAFNE
ESRF
Inserted “total” pump
SOLEIL
DIAMOND
RHIC
TiZrV NEG Coating Setup at CERN (TiZrV) Surface pump
diffusion barrier
F. Le Pimpec -/ SLAC
LHC
ILC ??...
26
What Makes NEG So Attractive?

A
GREAT Material
– High distributed pumping speed
– Initial photo, electron-desorption coefficient
lower than most technical material (Al - Cu
- SS)
– Secondary Electron Yield (SEY) lower than
that of common technical materials

Drawbacks
– Needs activation by heating (200°C to
700°C) - Pyrophoricity (Zr-based alloy)
– Does not pump CH4 at RT, nor noble gases
– Lifetime before replacement (thin film)
High H2 solubility but embrittlement (powder creation)
F. Le Pimpec - SLAC
27
Photodesorption hCO at c = 194 eV
1.E-03
NEG 0%
Sat
(13C18O) 13C18O
CO
ETA (molec/photon)
NEG St707
1.E-04
1.E-05
SS
1.E-06
1.E-07
1.E+18
Sat (13C18O) CO
1.E+19
1.E+20
1.E+21
NEG 100 %
1.E+22
1.E+23
Dose photons
An activated NEG desorbs less H2 CO CH4 CO2 than a 300°C baked SS
A saturated NEG desorbs more CO
a baked
F. Lethan
Pimpec
- SLAC Stainless Steel
28
Electrodesorption hCO at Ee- = 300 eV
1.E-01
CO
NEG Sat (13C18O) 13C18O
1.E-02
Eta (molec/elect)
NEG St707
NEG Sat by CO
1.E-03
Cu
1.E-04
1.E-05
NEG 100 %
1.E-06
1.E+16
1.E+17
NEG Sat (13C18O) CO
1.E+18
1.E+19
1.E+20
1.E+21
Dose Electrons
An activated NEG desorbs less H2 CO CH4 CO2 than a 120°C baked OFE Cu
surface.
A saturated NEG desorbs less *C*O than a 120 °C baked OFE Cu surface
F. Le Pimpec - SLAC
29
Also True For Thin films TiZr and
TiZrV
SS
Cu
F. Le Pimpec - SLAC
30
SEY & Electron Cloud
LHC
Electron cloud can exist in p+ / e+ beam accelerator
and arise from a resonant condition (multipacting)
between secondary electrons coming from the wall
and the kick from the beam, (PEP II - KEK B - ISR LHC).
3
Aluminium
Beryllium
Titane
2.5
NLC Fast Head tail
straight 1012
Secondary Electron yield
Copper OFHC
Stainless Steel
NEG St 707 (activated)
2
NEG TiZrV (activated 200°C- 2h)
1.5
1
0.5
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Electron Beam Energy (eV)
SEY of technical surfaces baked at 350°C for 24hrs
M. Pivi
F. Le Pimpec - SLAC
31
Getter SEY & Electron Cloud
Low SEY : Choice for the NEG of
the activating T and t .
Conditioning (photons eions)
Contamination by gas exposure,
or by the vacuum residual
gas, increases the SEY; even
after conditioning.
      e 1cos 
Scheuerlein et al.
TiZrV coating
Roughness is an issue to be
considered for lowering the SEY
TiZrV coating
Angles of
incidence, of
the PE, yield
the shape of the
curve toward
higher values
2 h at 300C, CO injected at NEG T=60C
F. Le Pimpec - SLAC
32
Pumping Speed
H2
CERN/EST group
Ti32Zr16V52 (at.%)
2 Hours Heating T (°C)
Pumping speed plots for getter are everywhere in the literature
• From sample to sample, pumping speed plots vary
• Many geometric cm2 are needed to see the pumping effects. Roughness (true
geometry)
•Temperature and/or time of activation is critical to achieve the pumping speed
required
•Capacity of absorption of the NEG is determined by its thickness
33
Installing a NEG : Yes or No ?
You want to answer the terms of this formula :
The tunneling ionization of molecules is not included, but should be for very short and intense
bunched beams (29 GV/m for CO ~7fs)
F. Le Pimpec - SLAC
34
Installing NEG : Yes ! …
Which NEG and where ?
– Linear pumping via ribbons ?
– Thin film coating on the accelerator chamber
itself ?
- “Ribbons” are reliable and have a good capacity time before saturation, few replacements over the
years (PEP II - LEP)
- Thin films allow easy reach of XHV (<10-12 Torr).
The lifetime can be long depending on the thickness, 3
years of use at ESRF in some sections.
Yes to all of that, BUT you need to activate !!!
F. Le Pimpec - SLAC
35
But !
In accelerator Cu, Al or SS are the technical
materials of choice, high conductivity
–
–
–
–
Cu and SS, can be baked at high temperature,
Al cannot (200°C)  special design, or ways, to
activate the NEG
SS and NEG coating have a lower conductivity
compared to Cu or Al, wakefield issues  skin
depth & vacuum chamber size determination
A leak during an activation might lead to
scrapping the chamber (2m of Be chamber,
vertex detector, for LHC 106 CHF)
Cycles of venting/activation need to be
assessed for the lifetime of the machine
F. Le Pimpec - SLAC
36
Conclusion
What is the requirement of the vacuum system ?
Pressure wise
Bakeout of the system
Pumping speed
Vapor Pressure
Vapor Pressure
Design to allow bake
Contamination Issues
Getter Element to use
Evaporable, Non-Evaporable : Design
Lifetime of the vacuum device
Capacity of the getter
Activation cycle - NEG
Evaporation cycle – EG
…
F. Le Pimpec / SLAC-NLC
37
Acknowledgement
SLAC :
R. Kirby
CERN :
JM. Laurent, O. Gröbner, A. Mathewson
–
…
F. Le Pimpec - SLAC
38
References
1.
2.
3.
4.
5.
6.
7.
8.
CERN web site and Summer lecture
AVS 50Th conference
Mc Graw-Hill Access Science
P. Danielson : Vacuum Lab
Electronics magazine: October 1950
CAS Vacuum Technology: CERN 99-05
USPAS - June 2002
SAES getters
9. Web surfing for the beautiful pictures
– …
F. Le Pimpec - SLAC
39
Some More References
11. http://www.nasatech.com/Briefs/Sept99/NPO20436.ht
ml
12. http://info.web.cern.ch/info/Press/PressReleases/Relea
ses1999/PR01.99Efire.html
13. http://www.metall.com.cn/cemm.htm
14. http://education.jlab.org/itselemental/ele055.html - Cs
getter
15. http://hcrosscompany.com/lampseal/tantalum.htm
16. http://www.fact-index.com/
17. http://www.bulbcollector.com/ (Thks Ed.V. Phillips)
18. http://www.centennialbulb.org/index.htm
19. http://wps.prenhall.com/wps/media/objects/724/74157
6/chapter_01.html
– …
F. Le Pimpec - SLAC
40