Promising Directions for Developing Nano-structured Photocathodes
Laboratoire de Chimie-Physique CNRS – Université Paris-Sud UMR 8000 91405 ORSAY Cs 2 Te...
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Transcript of Laboratoire de Chimie-Physique CNRS – Université Paris-Sud UMR 8000 91405 ORSAY Cs 2 Te...
Laboratoire de Chimie-PhysiqueCNRS – Université Paris-SudUMR 800091405 ORSAY
Cs2Te photocathodes
at ELYSE
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
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)
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
R.F. Gun & BoosterF = 3 GHz
10 cm
R.F. gun Booster
3 MeV9 MeV
Femtosecond Laser
~ 3 m transport
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
Accelerator Room
Diagnostics
1 m
Faraday cup charge Screen transverse beam size W.C.M. charge – position
Horizontal slit energy dispersion
Cerenkov radiator pulse width
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
Photocathode Cs2Te - = 20 mm
Cs = 16 nm
Te = 20 nm
Canon HFSection acc.
photocathode inside RF gun
Preparation chamber
Substrat Copper(polished)
Cathode manipulator
Cathode fabrication area
Cathode InsideRF gun
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
Preparation Chamber
PC
Te et Cs crucibles
heater micro-balance
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
Cs2Te deterioration
17 juin 200517 juin 2005
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)
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 )
…
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
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
Klystron – HF distribution
15MW
6 MW
0 - 6 MW
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
Recouvrement - cerenkovRecouvrement - cerenkov
Simulation E.G.S.
eau
verre
1 cm1 cm
vide
diode
air
eau
e-
Lumière CerenkovLumière Cerenkov
Recouvrement des faisceaux
air
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
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