Transcript Getters from Light Bulb to Accelerators

How DID they make light bulb
work ?
♦ Since 1800 the electric arc ♦ The problem was in
light was known. However,
the life time of a filament
made of carbon was poor.
obtaining a high enough
vacuum in the bulb and
getting rid of the oxygen in
the residual gas
Use of the first
Evaporable
Getters
Bulb Installed in 1901 at
the Livermore’s (CA) Fire
station. C filament - 4 W
Phosphorus pumped
lamp tend to have a
red cast
F. Le Pimpec
1
Choice of Getter – Vapor Pressure
When choosing a material to be used for
a vacuum application.
1
One question which need to be asked is :
At Which temperature my
system is going to be running ?
Zn
Mg
10-7
200
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
After Honig and Kramer (1969)
F. Le Pimpec
2
Ti vs Other Getters in Accelerator
Ba - Ca - Mg : High vapor pressure. Trouble if bake
out is requested
Zr - Nb - Ta : Evaporation temperature too high
1cm2
Typical sublimation rate 0.1 to 0.5 g/hr
0.5 g/hr ; MTi =48g/mol
0.5/(48*3600) = 2.9 10-6 mol.s-1
1ML~1015 atom.cm-2
2.9 10-6 mol.s-1. Avogadro =
1.74 1018 atom.s-1
1 ms is necessary to evaporate 1 ML
3 minutes = 180E3 ms hence ML for
1cm2
Ref. “Le Normand CERN vacuum note”
A) Pumping Speed calculated at RT
B) Wide variations due to film roughness
C) For H2, competition between desorption
and diffusion inside the deposited layers
Ref. “Sorption of Nitrogen by Titanium Films,” Harra and
Hayward, Proc. Int. Symp. On Residual Gases in Electron
Tubes, 1967
F. Le Pimpec
3
Also True for Thin Films TiZr and
TiZrV
V. Baglin et al.
F. Le Pimpec
4
Ionodesorption by heavy energetic
ions on technical surfaces
1.5 109 Pb53+ ions (per shot) under 89.2° grazing incidence and 4.2 MeV/u
E. Mahner et al.
F. Le Pimpec
5
SEY & Electron Cloud
3
Aluminium
Beryllium
Titane
2.5
Copper OFHC
Secondary Electron yield
fast head-tail instability
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).
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
F. Le Pimpec
6
SEY & Electron Cloud
Results vary
from sample to
sample
Roughness is
an issue
Low SEY : Choice of the activating temperature and time of the
NEG - or conditioning (e- photons ions)
Contamination by gas exposure or by the vacuum residual gas
increases the SEY
TiZrV coating
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
Hilleret et al.
F. Le Pimpec
7