laboratoire de chimie-physique cnrs – université paris-sud umr 8000 91405 orsay cs 2 te...
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Laboratoire de Chimie-PhysiqueCNRS – Université Paris-SudUMR 800091405 ORSAY
Cs2Te photocathodes
at ELYSE
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Choice of accelerator & cathodeChoice of accelerator & cathodePump probe experiments
(synchro. laser & electrons)
Small accelerator room
(existing building)
PhotoinjectorPhotoinjector
High charge > 1 nC
High Q.E.
(Laser energy max ~ 20 µJ)
Long lifetime
CsCs22TeTe
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Specifications for accelerator
Pulse duration 5 ps Charge 1 nC Energy from 4 to 9 MeV Repetition rate 50 Hz Energy dispersion 2,5 % Diameter on target 2 à 20 mm
1998 - choice of L.A.L. (SERA)
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Photo-injector
Laser – 263 nm
electrons
R.F. gun
Booster
photocathode
solenoid
F = 3 GHz
Design same as CERN/CTFFor RF gun & cathode preparationChamber (minor changes)
F = 3 GHz
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R.F. Gun & BoosterF = 3 GHz
10 cm
R.F. gun Booster
3 MeV9 MeV
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Femtosecond Laser
~ 3 m transport
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Accelerator layout
ProductionProductionof electrons of electrons
accelerationacceleration
transporttransport
RF gun, solenoid, boosterRF gun, solenoid, booster laserlaser
Preparation chamberPreparation chamber(in situ fabrication)(in situ fabrication) Experimental areasExperimental areas
triplettriplet
triplettriplet
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Accelerator Room
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Diagnostics
1 m
Faraday cup charge Screen transverse beam size W.C.M. charge – position
Horizontal slit energy dispersion
Cerenkov radiator pulse width
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History
January 2000 building construction –creation of L.C.P. April 2001 accelerator & laser moving form LAL to LCP Januray 2002 photocathode preparation chamber installation (CP) April 2002 first beam – 9 MeV (copper cathode) June 2002 conditionning cavities : 5 Hz - 10Hz - 25 Hz
CP leak, buiding chiller problem… April 2003 1st cathode CsTe : 6 nC May 2003 1st measurement @6 ps – 1,5 nC – 9 MeV October 2003 1st local users
… beam production for users, minor changes for accelerator October 2005 2nd CsTe photocathode ! … beam production for users
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Photocathode Cs2Te - = 20 mm
Cs = 16 nm
Te = 20 nm
Canon HFSection acc.
photocathode inside RF gun
Preparation chamber
Substrat Copper(polished)
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Cathode manipulator
Cathode fabrication area
Cathode InsideRF gun
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TeTe
CsCs
micro-balance
10 cm
Cathode fabrication-Copper substrat cleaned and outgased (400°C – 1h)
- Temperature ~ 110°C
- Monitoring of thickness during evaporation Te = 20 nm (10 min) Cs = 15 nm (45 min)
QE = 0,5%In operation
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Preparation Chamber
PC
Te et Cs crucibles
heater micro-balance
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Cs2Te lifetimeCs2Te-I life time
0
1
2
3
4
5
6
7
8
0 4 8 12 16 20 24 28 32 36 40 44 48 52
H.F. cumulated time (days)
Cha
rge
(nC
).
0
4
8
12
16
20
24
Lase
r en
ergy
(µ
J)
9 MeV
Elaser
laser diameter = 6 mm
18 mars 2003 20 june 2005
Laser diameter = 15 mm
Air exposition
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Cs2Te deterioration
17 juin 200517 juin 2005
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Vaccum conditions
P(PC) ~ 3 x 10-8 mbar (leak –porosity) P(PC) ~ 5 x 10-7 mbar during preparation P(gun) ~ 5 x 10-10 mbar (static) P(gun) ~ 5 x 10-9 mbar (with RF)
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Possible improvements
Add in situ current measurement during evaporation for optimisation
Try Mo substrate Better outgasing Add closing valve for separating crucible translator
(not much space )
…
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Accelerator performance
Pulse duration ~ 6 ps Charge : 0.1 to 6 nC Energy from 4 to 9 MeV Repetition rate : 0.1-0.5-1-2-5-10-25 Hz Energy dispersion 1 % Diameter on target : 2 à 20 mm
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Photo-current – Dark current
/ 50 = 5,8 nC
Iobsc
Iph
laser
Eaxe
F = 10 HzHF = 3 µsLaser = 2,7 µs
Direct leg : VD9 MeVEa = 70 MV/m
Qph = 5,8 nCQdark = 3,9 nC
Qdark/Qph = 67%
VD
VD1
VD2
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Klystron – HF distribution
15MW
6 MW
0 - 6 MW
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Implantation
Salle des baies Salle de contrôle
Salle de détection n1
Salle de détection n2
Salle de préparation
Salle machine
ascenseur local technique
local stockage
N
S
E O
2ème sous-sol2ème sous-sol
Aires expérimentales
KK MM AA
2ème sous-sol, bâtiment 349
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Recouvrement - cerenkovRecouvrement - cerenkov
Simulation E.G.S.
eau
verre
1 cm1 cm
vide
diode
air
eau
e-
Lumière CerenkovLumière Cerenkov
Recouvrement des faisceaux
air
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Yag-Ce – 40 mm(200 µm)VD2 – 9 MeVFwhm = 2 mm
saphir – 25 mm(500 µm)VD2 - 9 MeV30° view angleFwhm = 3 mm
25 mm40 mm
Beam size measurement (in air) Exit window (12 µm Al)
camera
vacuum
screen
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Pulse duration
0
0.05
0.1
0.15
0.2
0.25
0.3
0.2 0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.28 0.29 0.3
time (ns)
Inte
nsi
ty (
a.u
.)
jitter correction-200 shots
gaussian fit, FWHM = 5,8 ps
9 nov. 2004
FWHM = 5,8 psFWHM = 5,8 ps
9 MeV, Q = 1.6 nC
timetime
Wave lengthWave length
380 nm 620 nm
Cerenkov light