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9-Dec- 2002 R. Cimino LHC- Vac
Status report of the INFN SurfaceScience Laboratory now at CERN.
• The installed system and its characterization• What has been measured and its implication• What else (side activities)• Future work
R.Cimino and I.R. Collins
9-Dec- 2002 R. Cimino LHC- Vac
The installedsystem
• µ-metal chamber;• En. & angle res. analyser;• Low T manipulator;• LEED - Auger RFA;• Faraday cup.
• For details: see minutesof 18/2/2002 meeting
• or call in 30-1-044
9-Dec- 2002 R. Cimino LHC- Vac
• 3 slots: 1,2,3 mm wide• Gold plated• To measure actual Beam
current and size• Partly coated with
Phosphorous powder to “see”the beam
Thanks to E. Kos
Faraday cup
9-Dec- 2002 R. Cimino LHC- Vac
Characterization of the e- beam
• Find e- gun optimum lens voltages for:• Small spot: less than 0.5 mm in diameter• Position and intensity stability Vs Time, Energy and
Filament current.
• Stable between 50 and 400 eV.• Gun currents between few nAmps and µAmps
==> 20 µC/h/mm2 - 20 mC/h/mm2
• Intense spot with low background
9-Dec- 2002 R. Cimino LHC- Vac
Characterization of the RFA asan electron energy analyser
• On Au sample Vs Electronenergy and Sample Bias:
• Need of a Bias voltage tomeasure Secondaries fromsample and not a superpositionof them and those producedinternally by the grids of theanalyser.
0 10 20 30 40 50 60 70Energy (eV)
-20 Volt Bias
0 Volt Bias
Analyser secondaries
True secondaries
9-Dec- 2002 R. Cimino LHC- Vac
Characterization of the electronsource and sample Bias
• The actual Primary energyimpinging on the sample is:
Ep = Egun + E bias
• It is possible to vary Egunand E bias to measure atlow Ep keeping the Egun ina region where it is stable(>50 eV) and recording EDC.
0 20 40 60 80 100In
tens
ity (
a.u.
)Energy (eV)
- 20 Volt Bias
0 Volt Bias
Ep=80 eV
Ep=100 eV
Ep=50 eV
- 50 Volt Bias
Egun=100 eV
9-Dec- 2002 R. Cimino LHC- Vac
Characterization of EDC line-shapeas a function of analyser resolution• The actual EDC
line shape is animportant
parameter ofthe BIEM
simulation codes.• All measured data
have an An.Res.=1.2 eV
• The measured line-shape depends on the an. Res.
0 10 20 30 40 50 60 70
An. Res=1.2 eVAn. Res=3.8 eVAn. Res=8.0eV
Primary Energy (eV)
Ep=60.3 eV
9-Dec- 2002 R. Cimino LHC- Vac
10 18 26
D 2
As receivedafter WL exposureafter Ar+ sputtering
Kinetic
Inte
nsity
(a.u
.) hn =30 eV
34 42Energy (eV)
x 50
Characterization of EDC line-shapeas a function of analyser resolutionPhotoemission results
(R. Cimino, I.R. Collins, V.Baglin Phys. Rev. Acc. &Beam 2, 63201 99) doshow, on some as-received samples,
very sharpsecondaries.
• Data will be collected with better res. (<0.1 eV)
9-Dec- 2002 R. Cimino LHC- Vac
Measure of Secondary e- YIELD
• At each Primary energy wecan measure Igun (with theFaraday cup) and Isample.
Igun - Isample
Igund =
N.B. System not optimized to measure SEY
0.9
1.0
1.1
1.2
0 100 200 300 400
d
Primary energy (eV)
Au
9-Dec- 2002 R. Cimino LHC- Vac
• Energy Distribution Curves as function of Ep
0 80 160 240 320
Ep=312 eV
Kin. En. (eV)
Secondaries
Reflected electrons
What has been measured on f.s. Cu
0 80 160 240 320
Ep=212 eV
Kin. En. (eV)
Secondaries
Reflected electrons
9-Dec- 2002 R. Cimino LHC- Vac
• Energy Distribution Curves as function of Ep
0 40 80 120 160
Ep=162 eV
Kin. En. (eV)
Secondaries
Reflected electrons
What has been measured on f.s. Cu
0 60 120
Ep=41 eV
Kin. En. (eV)
Secondaries
Reflected electrons
9-Dec- 2002 R. Cimino LHC- Vac
What has been measured on f.s. Cu• Energy Distribution Curves as function of Ep
0 4 8 12 16Kin. En. (eV)
Ep=11 eVSecondaries
Reflected electrons
0 4 8 12 16
Ep=3.7eV
Kin. En. (eV)
Secondaries
Reflected electrons
9-Dec- 2002 R. Cimino LHC- Vac
What has been measured on f.s. Cu• Integrating the curves
gives the Percentageof Secondaries andReflected electrons
0 20 40 60 80 100 120Kinetic Energy (eV)
Ep=112 eV
Secondaries
Reflected electrons
• To separate “truesecondaries” from“rediffused electrons” isarbitrary and has notbeen considered in thisanalysis.
9-Dec- 2002 R. Cimino LHC- Vac
Secondariesand
ReflectedElectronVERSUS
PrimaryEnergy
What has been measured on f.s. Cu
0.0
20.0
40.0
60.0
80.0
100.0
0 50 100 150 200 250 300
Primary Energy (eV)
Secondaries
Reflected electrons
Perc
enta
ge
9-Dec- 2002 R. Cimino LHC- Vac
What has been measured on f.s. Cu
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250 300 350
d
Primary Energy (eV)
d Total
Contribution of reflected electrons to d
Contribution of secondaries to d
• we can single outthe contribution tod of the secondariesand the reflectedelectrons versusprimary energy.
Igun - Isample
Igund =
9-Dec- 2002 R. Cimino LHC- Vac
Implication• Low energy electrons have a long survival time (in agreement
with observation on PSR at LANL…).• In FELs a low repetition rate is supposed to ensure no e- cloud
problems. BIEM has to be considered.• BIEM simulations need to be updated for the LHC.
• Reflected el. are NOT absorbed and do notdirectly contribute to heat load !!!
• However they will be accelerated by thefollowing bunches, gaining energy to bedeposited on the BS.
9-Dec- 2002 R. Cimino LHC- Vac
• There is an on-going collaboration between INFN and INFMto use XMOS, a bending magnet beamline at ELETTRA (TS)to measure the photon reflectivity as recommended by theLHC MAC (forward scattered and diffuse) from the LHCsawtooth structure as well as flat Cu samples to quantifysawtooth efficiency in reducing the presence ofasynchronous source of electrons in the LHC.
• (first beamtime allocated 6-12/Feb. 2003)
What else?
9-Dec- 2002 R. Cimino LHC- Vac
• e- induced EDC of Cu and study of the secondaryversus reflected component at very low primarye- energy (1-300 eV Ep) as a function of:
-Analyser resolution; (Possibly angle of inc. and em.)
- Space charge- Samples and sample spot (as received samples are NOT
identical nor homogeneous)
- At RT and below 20 K (in presence of adsorbed gas on thesurface).
- Possibly Vs Scrubbing (as a function of scrubbing e- energy)
Objectives for next 6 months…..
9-Dec- 2002 R. Cimino LHC- Vac
• Possibly correlate those results with surfacecomposition changes monitored by in situ Augerspectroscopy.
Objectives for next 6 months…..
0 4 8 12Kinetic Energy (eV)
E.D.C. Ep=10 eV
Cu at 10 K
100 200 300 400 500
dN(E
)dE
Kinetic Energy (eV)
AUGER at 10 K taken "in situ" after EDCs.
CO
CuOx
Ep=3keV
Cl
9-Dec- 2002 R. Cimino LHC- Vac
• Possibly correlate those results with surfacecomposition changes monitored by in situ Augerspectroscopy.
Objectives for next 6 months…..
•To Give a deeper understanding of the chemical processesoccurring at surfaces, for example: from LHC PR 472:“…Although the phenomenon of conditioning has beenobtained reproducibly on many samples, the exactmechanism leading to this effect is not properlyunderstood. This is of course not a comfortable situationas the LHC operation at nominal intensities relies on thiseffect…”
9-Dec- 2002 R. Cimino LHC- Vac
• Possibly correlate those results with surfacecomposition changes monitored by in situ Augerspectroscopy.
• Understand the implication of low energyelectrons to the LHC, by setting up anexperiment in order to measure the actual heatload per electron as a function of its energy(10-200 eV).
• Measure the photon reflectivity
Objectives for next 6 months…..