[PPT] - CERN Lab activities related to PHIN 1. DC and RF gun results with PowerPoint Presentation

SLIDE 1

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

CERN Lab activities related to PHIN

1. DC and RF gun results with cesium telluride photocathode :

a) Cathode produced by the standard evaporation process b) Cathode produced by co-evaporation

2. CTF3 photocathode requirements
3. Photocathode studies: CERN proposal
4. The CTF3 photo-injector: CERN part
5. Installation
6. Schedule

SLIDE 2

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Standard evaporation process : Cs2Te typical results

Standard evaporation process means : evaporation of an alkaline layer over a tellurium layer on different substratum

10 ps 6 ns Pulse width (FWHM) 10-10 mbar few 10-11 mbar Storage vacuum pressure 1 – 5 x10-9 mbar 10-10 mbar Working vacuum pressure Few weeks Few months (extrapolated) Typical lifetime with QE > 1.5 % 2 % ≤ QE ≤ 8 % 4 % ≤ QE ≤ 22 % Starting QE Cu – Au (?) Au Best substratum 8 µA 1 mA Higher mean current Few kA 20 A Peak current 100 MV/m 8 MV/m

Nom. electric field

RF gun (49 cath.) DC gun (35 cath.)

Typical results with Cs2Te

SLIDE 3

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Standard evaporation process : High charge test (mC)

Cs2Te photo-cathodes tested in the DC gun @ 9 MV/m Up to 300mW UV on the cathode ; 100 ns pulse length, 10 A, 1kHz Rep.Rate

CTF3 average current CTF3 QEmin

Up to QEmin = 3 % Cs2Te photo- cathodes fulfill CTF3 specifications

CTF3 requested charge 5.4 µC macro-pulse 10 Hz 40 working hours CTF3 QEmin CTF3 requested lifetime

Jmax = 21 mA/cm2 Fmax = 6 W/cm2 @ 266 nm

SLIDE 4

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Recap of photocathode studies

Since 1991 we tested many sorts of photocathodes :

1.

Metallic photocathodes : Al, Au, Cu, Mg, Mo, Sm, Y

QE < 10-3 even with special treatment (etching, laser conditioning)
QE too low for high charge production : very high powerful laser and/or plasma production at the
photocathode. Not suitable for our application

2.

Alkali-antimonide photocathodes : Cs3Sb, K2CsSb, K3Sb

Need ultra high vacuum
Good QE at visible light but lifetime too short (few hours) not suitable for our application

3.

Alkali-telluride photocathodes : Cs2Te, Rb2Te, RbCsTe, Li2Te

Need UHV
RbCsTe and Rb2Te : possible rejuvenation after air exposure by heating or etching
Cs2Te : standard photocathode for our applications : few % during weeks at high charge and high

electric field (up to 120 MV/m)

4.

Other photocathodes : CsI, CsI+Ge, Cs3As, GaAsO, PLZT, TiO2

CsI+Ge had been used from 1994 to 2000 in the Probe Beam RF gun because it is air transportable
We had no success with the GaAs activation for e-pol. production : preparation chamber not adapted to

this application

Photocathodes were deposited on different substrates (Al, Au, Cu, Mg, Mo, Stainless Steel) chemically cleaned and/or cleaned by argon ion bombardment : Cu with chemical and etching cleaning with RF conditioning seems to be the best for high electric field.

SLIDE 5

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Co-evaporation process

2 4 6 8 10 12 14 50 100 150 200 250 300 350 Working hours QE (%)

67 days

Cath. 144

in the RF gun

QE(t) = QE1.e(-t/τ1) + QE2.e(-t/τ2) Mean lifetime (4 cath.) in the DC gun @ 8 MV/m p ≤ 10-10 mbar Mean lifetime (9 cath.) in theRF gun 100 MV/m ; 2*10-9 ≤ p ≤ 7*10-9 mbar Mean lifetime (5 cath.) during storage in the T.C. p ≈ 3*10-11 mbar

3 % 55 h

14.9 Average 22.5 Max 8.2 Min QE(%) 20 cath. 315 3.4 14 9.2 RF gun 779.5 12.74 65.9 2.24 DC gun 3311 9.17 18.9 3.85 Transport carrier τ2 (h) QE2 % τ1 (h) QE1 % QE = f (t)

Evaporation at room temperature

nm/mn nm

Evap. rate

Thickness 0.5 - 2 0.1 – 0.5 3.9 - 49 1.3 - 11 Cesium Tellurium

SLIDE 6

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Photocathode Requirements for the CTF3 - DB

Photocathodes with a QE ≥ 3 % during at least 40 working hours A photocathode production to guarantee a continuous run of at

least 6 months For that we have to do :

A complete maintenance of the preparation chamber and of the transport carrier (for CTF2 and CTF3 thermoionic gun area installation) Adapt the RF gun transfer chamber (MPC) to the new gun and to the new sites (we assume the same photocathode plug) Re-use and/or develop an automatic RF conditioning process Pursue photocathode studies mainly to increase the lifetime, the reproducibility, and to fulfil the CLIC requirements Design and built new transport carrier and/or MPC for installation in the CTF3 linac area (not scheduled)

SLIDE 7

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Photocathode studies – CERN proposal

Reproducibility of alkali-telluride photocathodes produced by co-evaporation
Study of alkali-antimonide photocathodes produced by co-evaporation
Comparison between telluride and antimonide cathodes for the CTF3 specifications

UV laser beam Shutter Cs & Te Evaporators Cs thickness measurement Te thickness measurement Electron collect. electrode RF

ven

Photocathode plug UV laser beam Shutter Cs & Te Evaporators Cs thickness measurement Te thickness measurement Electron collect. electrode RF

ven

Photocathode plug

Preparation chamber developments

Stoïchiometric ratio measurement
Evaporation rate control
Evaporator design for co-evaporation

Te 36 mm Cs

SLIDE 8

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

The CTF3 photo-injector

RF Network

Laser Beam Line 0.37µJ / µPulse 2310 µPulses

Electron Beam 2.33 nC /µPulse

Freq. X 4

λ = 262 nm Power Amplifier Wtrain = 1.6 J ; Ptrain = 16 kW λ = 1047 nm 10.3 µJ / µPulse Pulse width ≤ 10 ps Pulse duration = 100 µs

Transport carrier

3 GHz RF gun E = 85 MV/m U = 5.6 MeV I = 3.5 A Cs2Te cath QE = 3 % Master oscillator λ = 1047 nm f = 375 MHz P = 1 W W/µPulse = 2.7 nJ Pulse shaping Photocathode preparation chamber

Under the responsibility of CLF-RAL Under the responsibility of LAL Orsay LAL - Orsay Under the responsibility of CERN Collaboration RAL – LOA CERN

Total efficiency IROUT ⇒ UV

cath = 3.6 %

Time interval division ∆t = 0.667 ns Phase coding 3 GHz RF source Pre-amplifier λ = 1047 nm PQCW = 50 W W/µPulse =133 nJ

KLYSTRON 3 GHz - 30 MW 375 MHz 3 GHz

SLIDE 9

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Pulse Train production

2.668 ns 1.334 ns

667 ps

PC Driver

RF = 2.99855 GHz

333 ps

Time structure generation of the CTF3 Drive Beam Photoinjector

I I I First splitting Second splitting Delay of 1 rf period and recombination I = Laser bunch intensity 53 bunches 1 ns 333 ps

Even sub-pulse 212 bunches : 140.74 ns Odd sub-pulse 212 bunches : 140.74 ns

t = 0

667 ps

2xI

1.334 ns 1.334 ns

2xI Two train generation 106 bunches Pulse shaping : T = starting sub-pulse + 5 odd sub-pulse + 5 even sub-pulse = 1.548 µs 2120 bunches + starting bunches Starting bunches Starting sub-pulse 4xI

SLIDE 10

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

CTF3 photo-injector: CERN participation

Laser :

Pulse train generation Pockel’s cell study Harmonic conversion efficiency study Laser monitoring Feedback control, amplitude regulation Automatic control of the laser beam position

Timing Photocathodes

Maintenance of preparation chamber, TC and MPC

RF power Installation and commissioning

SLIDE 11

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Installation : Photo-Injector in the CTF2

CTF 3 CTF 2

5 m

Light hole Wave guide hole

Optical table 1.5 x 3.5 m 6 electr. racks

Laser room

RF test stand Photo-injector

Install controlled entry Suppress controlled entry Install shielding wall

Drill holes Φ 120 mm Separate the 2 clim. stations

Clim. Clim. 30 GHz , 200 MW , 150 MV/m 400 ns , 50 Hz , 30 cm

Dump MPC TC 1.5 x 1.5 m

5 MeV ; 3.5 A ; 1.5 µs ; 10 Hz

SLIDE 12

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Installation : Photo-Injector in the CTF3

Laser room CTF 3

Photo-injector 5 m

Light hole Laser hole

RF test stand

MPC TC

CTF 2 Photo-injector as the CTF3 source

SLIDE 13

G. Suberlucq CERN

CARE PHIN JRA2 Meeting 19/11/2003

Schedule

Realization of the photo-injector option in two steps :

Operational photo-injector in the CTF2 in the end of 2006

Operational photo-injector in the CTF3 in the middle of 2007

Installation during the shut-down 2006-2007 Commissioning spring 2007