Overview of Advanced Surface Science activities at CERN

Overview of Advanced Surface Science
activities at CERN
S.Calatroni, M.Taborelli
TE-VSC-SCC
Basic components of particle accelerators
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
2
Magnets
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
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3
Accelerating cavities
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Technology Department
10 October 2014
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4
The world’s longest vacuum system (about 100Km):
- Pressure ranges down to XHV in LHC (<10-12 mbar)
- Necessary to reduce the beam/gas interaction (defocussing, energy
spread, lifetime, noise in the detectors of the experiments)
- Pumping is achieved by mechanical pumps, ion pumps, cryopumping
and getters
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
5
Particle detectors
CMS
ATLAS
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
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Activities: Surfaces Chemistry and Coatings
Most accelerator components require some kind of surface treatment or
surface modification:
• Surface modification by surface finishing (UHV grade cleaning,
etching, electroplating, electrochemical characterization…)
• Thin film PVD coating (magnetron sputtering, evaporation)
• Surface characterization and analysis (XPS, Auger, Secondary
Electron Yield, emissivity)
• Chemical analysis (FTIR, UV-vis, Gas Chromatography, atomic
absorption spectroscopy, DSC,….)
The goal is to guarantee, maintain and improve the performance
of the accelerators and detectors in terms of availability, quality,
lifetime of components: research and development, prototyping,
production, control
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
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Preparing components for UHV or for subsequent treatments
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
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80
Transmittance [%]
40
60
Transmittance
[%]
100
Monitoring cleanliness for
UHV components:
CH
stretching
of CH3
20
CH3
Si-O-Si
symmetric stretching
deform. of
Si-CH
2000
1000
3 1500
0
FTIR
Through elution with C6H14
4000
3500
Si-C
stretching
and CH3
rocking
CH3
asymmetric
deform. of
Si-CH3
3000
2500
Wavenumber cm-1
Wavenumber [cm-1]
C:\OPUS_NT\MEAS\OILS AND GREASES\RHODORSIL OIL; SILICONE OIL.0
S.Ilie, C.Petitjean, C.Dias-Soares
solid
2003/07/16
180000
19%C
Fe2p
XPS
Intensity [a.u.]
Cr2p
O1s
Stainless steel 316LN
160000
140000
C1s
120000
28%C
100000
80000
58%C
P2p
60000
40000
S2p
20000
0
800
700
600
500
400
300
200
100
0
Binding energy [eV]
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
9
Copper plating of large objects (DTL tank)
Difficult to obtain uniform plating
Small ratio bath-volume to surface
Final assembly with the
electrodes for the
accelerator
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
10
Plating of many different metals: Ag, Au, Rh on the LHC
RF-contacts
Rh/Cu
Au/CuBe
Ag/CuBe
Inserted in the
machine vacuum:
cleanliness and purity
to avoid degassing !
The Ag and Rh
combination provides
good electrical contact
without cold-welding
in vacuum
Radiography, installed
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
11
Optimization of current profile for the Electropolishing of Nb
superconducting RF cavities (SPL)
5-cell cavity
Electrode and current
Simulation with smooth electrode (red) and optimized
electrode (with protrusions) to get more uniform
current and polishing (blue)
J profile - β-1-SPL - optimised
Current density (A/m2)
450
400
Standar
d
350
300
250
optimis
ed
200
150
0
200
Vacuum, Surfaces & Coatings Group
Technology Department
400
600
800
1000
1200
Distance along anode (mm)
10 October 2014
1400
1600
1800
2000
S. Calatroni & M. Taborelli
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Coating of vacuum chambers
DC-magnetron sputtering with target made of intertwisted wires of
Ti, Zr, V: developed at CERN in 1998. Patented and licensed to industry
Before
aftercoating
coating
Activation temperature (~180 ºC) compatible with copper vacuum
chambers (does not deteriorate too much the mechanical properties).
Used for the LHC accelerator for pumping and low Secondary Electron
Yield (dmax=1.1 after activation) in 6 km of Long Straight Sections
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
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Cylindrical Magnetron configuration
•
•
General
NEG
Proces Gas Ar
TUBE
B
3mm
wires of
Ti, Zr
and V
Ar+
- 500 V
Vacuum pumps
Ideal for vacuum chamber that needs a coating
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
14
Coating plant for LHC – LSS and detector chambers up to 7 m length
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
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Lab size DC-magnetron sputtering facilities
•
•
•
From small size substrates up to 1.2 m
length, rotations for complex shapes
Up to 3 independent targets for alloy
deposition with tunable composition
Typical materials:
- Cu, Au
- Ti
- NEG (TiZrV)
- Nb
- B4C
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
16
Cylindrical configuration
Internal coating of object without flanges: in vacuum chamber
Øin = 10 mm
Ø 200 mm
PS-booster pick-up
Aegis H-bar cooling trap
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
17
HIE-ISOLDE upgrade project
High Energy and Intensity – Isotope
Separator On Line DEtector
 Boost the radioactive beam energy from 3MeV/u to 10MeV/u by using SC linac.
Quarter-wave resonator (QWR):
Nb thin film sputtered
on 3D forged OFE Cu substrate
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
19
Nb/Cu cavities: HIE-ISOLDE
Substrate preparation (electropolishing or chemical
polishing) are crucial for the success of the coating
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
20
Coatings preventing electron cloud
+
Proton bunch (charge +)
Gas molecule
Electron (charge -)
The beam is perturbed by the electron multiplication; the
problem is more important for high beam currents (beam potential)
and short bunch spacing
To reduce the effect one must reduce the Secondary Electron
Yield of the walls or attract the generated electrons by other means
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
21
The possible solution : carbon a-C coatings
1.2
Dose below 10-6 Clb/mm2
1.1
1.0
SEY
0.9
0.8
0.7
CNe14 as recieved
0.6
CNe14 after about 1 month
air exposure
0.5
0.4
0
200
400
600
800 1000 1200 1400 1600 1800 2000
energy [eV]
-a-C coating on copper deposited by magnetron sputtering (in Ne)
-as expected SEY does not change for thicknesses above 50 nm
-development started in 2008
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
22
Measurement of SEY developed in-house
electron gun
Ip
A
Ic
Ic
Sample
Is
A
I p = Is + I c
SEY
measurement
XPS
d = Ic / (Is + Ic)
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
23
XPS: comparison with graphite
120000
Intensity [a.u.]
C1s
C1s
HOPG
CNe17
100000
80000
a-C(Ne)
60000
HOPG
cleaved
in air
40000
20000
0
292
290
288
286
284
282
280
278
Binding energy [eV]
The C1s peak is wider than that of freshly cleaved graphite: due to the
oxygen on the surface (8-10% typical) and chemical shift of C-O
bonds or due to the more disordered structure and different C-C
bond species?
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
24
Introduction: SPS dipoles
Almost 5 km of the SPS are filled with MBB and MBA type dipoles (>700).
The length of each dipole is 6.5 m and weights ~18 tons.
The beampipes are embedded in the yoke.
coat new beampipes, open the dipole,
exchange beampipe, close the dipole.
coat the actual beampipes directly in
the dipole.
Easy to coat
Too expensive (open/close dipole)
Difficult
coat
Easy toto
coat
cheaper
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
25
DC hollow cathode
Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS)
Graphite targets
(cells)
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
26
DC hollow cathode
Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS)
MBB dipole
Graphite targets
(cells)
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
27
DC hollow cathode
Coat actual beampipes by DC Hollow Cathode Sputtering (DCHCS)
THE TECHNIQUE IS MATURE FOR LARGE SCALE PRODUCTION
Graphite targets
(cells)
Pressure: 1.1 x10-1 mbar (Ar)
Power: 0.9 kW (1.5A @ 600 V)
0.5 mm in 20 hours
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
28
Research interests
- Treatments or coatings to lower the SEY of insulator surfaces, like
alumina, and metals
- NEGs with lower activation temperature than TiZrV
- Simulations of plasmas and sputtering profiles for coating systems
- Methods to produce thin films of refractory metals in small diameter
tubes (< 10 mm), including electrochemical means
- HIPIMS on SC RF cavities and more
- Structured films
- Coatings as permeation barriers for high transparency vacuum
chambers
- flexible (!) insulating coatings
- Coating/treating of long (30m) accelerator vacuum systems without
dismounting the beamline
- Novel cleaning techniques for UHV applications
- Simulation of electrochemical processes in complex geometries
Vacuum, Surfaces & Coatings Group
Technology Department
10 October 2014
S. Calatroni & M. Taborelli
29

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