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