ctf3 photoinjector konrad elsener for the photoinjector team

2 December 2008CTF3 photoinjector

CARE08 Highlight Talk – presented by K. Elsener 1

CTF3 photoinjector

Konrad Elsenerfor the Photoinjector Team

We acknowledge the support of the European Community Research InfrastructureActivity under the FP6 “Structuring the European Research Area” programme

(CARE, contract number RII3-CT-2003-506395)



CTF3 photoinjector: A successful collaboration inside JRA “PHIN” – Charge Production with PHoto INjectors

University of Milano

M. Divall (“consultant”)

INFN Frascati

CEA (Califes laser)



A huge effort in all the labs involved –

a big THANK YOU to everyone

(apologies for not mentioning any individual names)



Outline

1. Introduction

2. Overview: Photoinjector for CTF3

3. Recent progress- Installation RF gun- Laser system- Photocathode

4. First electron beam results

5. Summary and Outlook



1. Introduction

• two photoinjectors at CERN CALIFES (probe-beam in CLEX) PHIN (initially on test-bench in CTF2 building,

later to become CTF3 drive beam injector)

- normal conducting RF guns (inspired by CERN “gun IV”)- Cs-Te photocathodes- pulsed UV laser light to produce electrons

• differences in the design parameters



TL2

D FFD

D F D

D F D D F D

D F D

DF DF DF DF DF DF DF DF DF

D F D

F DF D

D FFFDD

D F DD F D

D F DD F D D F DD F D

D F DD F D

DF DF DF DF DF DF DF DF DF DFDF DF DF DF DF DF DF DF DF DF DF DF DF DF DF DF

D F DD F D

F DF DF DF D

Drive Beam AcceleratorDL

DL = Delay Loop (factor 2)

CR

CR = Combiner Ring (factor 4)

CLEX

Injector with thermionic gun

CALIFESPHIN



Main challenges – CTF3 “PHIN” electron beam (2007)

trains of 10 ps pulses at 1.5 GHz (synch. 3 GHz):1908 pulses in 1272 ns long train

(odd/even sub-pulses, 140.7 ns)2.3 nC per pulse, charge stability 0.25% -> 3.5 A current in the pulse trainneed 370 nJ UV laser pulse energy... ...for given 3% photocathode quantum efficiencyneed 15 kW IR laser power in the pulse train

repetition rate: 5 Hz



2. Overview: Photoinjector for CTF3

Main Design Parameters (2007)

PHIN

RF frequency [GHz] 2.9985

RF power [MW] 30

beam energy [MeV] 5-6

beam current [A] 3.5

number of bunches 1908

bunch spacing [ps] 666.7

charge per bunch [nC] 2.3

repetition rate [Hz] 5

bunch length FWHM [ps] < 10

rms. energy spread [%] < 2

n. emittance [mm mrad] < 25

vacuum pressure [mbar] < 2 x 10-10

lifetime of thephotocathode ?



vacuum requirements 2x10-10 mbarare a challenge-> 5 ion pumps

to further improve the dynamic behaviorof pressure:-> 42 holes (d=4mm) between RF gun and NEG chamber

courtesy LAL



17 Jan 2007 – LAL (presentation R. Roux)



29 April 2008 – LAL (photo G. Bienvenu)



3a. Recent Progress - Installation

19 June 2008 – CERN (CTF2)



cathode manipulator RF gun diagnostics (emittance meas.+ spectrometer)




16 September 2008 – CERN (CTF2)



3b. Recent Progress - Laser

3-pass Nd:YLF amplifier

2 pass Nd:YLF amplifier

Optical gate (Pockels cell)

PC

24

1.5 GHzNd:YLF

Oscillator +Nd:YLF

Preamplifier1047nm

Micro pulses at 1.5 GHz

~667ps; 10W

400s amplification window

for AMP1 Macro pulse

200s amplificationwindow for AMP2 Macro pulse

UV

t t

Green

t

IR Pulse

picker



0 100 200 300 400

6

5

4

3

2

1

0

laser beam after 2nd amplifier

time [s]

power [kW]

N.B. Output Amplifier 1: 3 kW – as specified Output Amplifier2: 6 kW – factor ~2 missing



laser beam after pockels cell(observed with photodiode + scope)

2 s

667 ps



IR

energy within 2ms gate

GREEN

energy within 2ms gate

UV

Energy within

2ms gate

Amp1 @90amps

PC on 2s

( Best Result )

(4.15-1.33)mJ

std=0.06mJ

~1.2 mJ

Std=0.016mJ

0.398 mJ

Std=0.012

133.3 nJ * in a micro pulse

~44 % efficiency

~34 % efficiency

Amp1 + Amp2 @90amps

PC on 2s

(12.3-4.2)mJ

std=0.26mJ

3.23 mJ

Std=0.07mJ

40%

efficiency

0.692 mJ

Std=0.024

~234 nJ * in a micro pulse

22% efficiency

* measured on laser table – nominal 370 nJ on photocathode

conversion to UV



more details on the laser system:

Massimo Petrarcatoday at 15:30

in Room A



0

2

4

6

8

10

12

14

16

0 200 400 600 800 1000 1200

time [h]

Qua

ntum

Eff

icie

ncy

[%] data taken in DC-gun, 80 kV (-> 8 MV/m)

29 Nov. 2007 Xmas break 9 Jan. 2008

CTF3 photoinj.

specification

Photocathode No. 167 (Cs-Te co-evap.)

3c. Recent Progress - Photocathode

caution:

QE not measured since January

QE in RF gun tends to be smaller



end of October 2008 – ready to go !



4. First electron beam results

! PRELIMINARY ! - RF conditioning with Cu plug, solenoids OFF- RF conditioning with Cu plug, solenoids ON- RF conditioning with CsTe cathode- 5 Nov.: first beam

Timing problem laser vs. RF pulse;

Short dark current pulse at the end of rf pulse clearly visible;

Intensity roughly equal to a single bunch



- 6 Nov.2008: first electron beam- RF phase adjusted; solenoid currents lowered - optimised

first MTV screenbeam spot 1.55 mdownstream of RF gun:FWHM ~ 5 mm



Beam current – 1.3 s train (2000 bunches)

Faraday Cup

Beam Position MonitorSum Signal

electron beam train-to-trainintensity fluctuations (BPM):r.m.s < 6% (5 minutes)

laser beam train-to-trainUV energy fluctuationsin laser room:r.m.s < 3% (500 trains)



Phase scan, 50 ns e-beam pulse train

100 deg.



Asymmetry in beam focusing behavior; problem seems to be in horizontal plane, behavior in vertical

seems ~ OK

Cause? Laser spot asymmetry, alignment, RF-asymmetry, solenoid alignment – to be checked in 2009

Beam size scan



Energy measurement, 90 deg. Spectrometer

Measured nominal energy with small energy spread (calibration to be checked)

5.3 MeV with 27 keV (0.5 %) r.m.s. energy spread

background(dark-current)subtracted



PHIN design achieved Nov. 2008

RF power [MW] unloaded 13 13

beam energy [MeV] 5-6 5.3

beam current [A] 3.5 < 0.2*

number of bunches 1908 < 3000

bunch spacing [ps] 666.7 666.7

charge per bunch [nC] 2.3 < 0.1*

repetition rate [Hz] 5 0.8

bunch length FWHM [ps] < 10 < 10 ?

rms. energy spread [%] < 2 < 1

Overview of Results

* combination of low QE (old cathode); laser energy not nominal; possibly laser beam not well centred on cathode (diagnostics !)




• after years of work, and a huge effort by all partners we had FIRST BEAM in the PHIN CTF3 photoinjector !

• many of the beam parameters measured are already the nominal parameters + stability is quite good !

• All in all, a GREAT ACHIEVEMENT !• next run: March 2009 (3 – 4 weeks) (availability of klystron)

• workplan: 3 new photocathodes; improved laser amplifier 2improved laser beam diagnosticsimproved electron beam diagnostics (screen sensitivity)-> significant increase of electron intensity-> detailed emittance measurements




• later in 2009: further improvements on laser system

(conversion crystals, amplifiers)additional work: phase-codingavailability of klystron ? - cf. CTF3 general schedule

A lot of work ahead -but good prospects to reach much higher intensity in 2009 !



Extra Slides



Photoinjector PHINCharge versus Train Length - 14/11/2008 with Amplifier 2 On

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500

Train Length (ns)

Ch

arg

e (

nC

)

N.B. Bunch Train 2 S not fully transported to Faraday Cup



4. Status of the photocathodes

Cs – Te photocathodes (theoretically: Cs2Te)successfully used at CTF2

progress in recent years:co-evaporation of Cs and Te onto copper substrate

photocathode production• “in-situ” for CALIFES (cf. CTF2)• in the photoemission lab for PHIN



4. Status of photocathodes4b) Photocathodes for PHIN – Photoemission Laboratory

manipulator

DC- gun

preparation

chambertransport

carrier

~ 1.4 m



4. Status of photocathodes

4b) Photocathodes for PHIN

UV laser beam

Shutter

Cs & TeEvaporators

Cs thicknessmeasurement

Te thicknessmeasurement

Electron collect.electrode

RFoven

Photocathodeplug

UV laser beam

Shutter

Cs & TeEvaporators

Cs thicknessmeasurement

Te thicknessmeasurement

Electron collect.electrode

RFoven

Photocathodeplug

special features:observe photoelectronproduction by UVduring the evaporationprocess

quartz monitors are calibrated

co-evaporation ofTe and Cs (masks!)

view inside the preparationchamber





on the “arm” inside

the transport carrier:

up to 4 plugs





1992-2002 large number of photocathodes produced(e.g. 58 Cs-Te for CTF2 drive beam)

... work in the lab ...

Dec. 2006 photocathode No. 166 (before bake-out of the vacuum system)-> Quantum Efficiency in DC gun 6.2%

2007 tests, bake-out, calibration of thickness monitors, improvements to masks, etc.

Nov. 2007 photocathode No. 167 produced under “correct conditions”



19 August 2008 – CERN (CTF2)



26 October 2008 – CERN (CTF2)



Energy measurement, Phase scan

Very reasonable behavior



Emittance

Öznür MeteEmittance= 4.88 mm mrad

‘to good to be true’



RF GUN CTF2 , Simulations ref

0 20 40 60 80 1000

2

4

6

z

En

erg

y

0 20 40 60 80 1000

1

2

3

z

bu

nch

len

gth

(p

s)0 20 40 60 80 100

0

0.1

0.2

z

Bea

m S

ize

x (

cm)

0 20 40 60 80 1000

0.1

0.2

z

Bea

m S

ize

y (

cm)

0 20 40 60 80 1000

10

20

z

Em

i x

0 20 40 60 80 1000

10

20

z

Em

i y

E= 5.4 MeV

E/E= 0.6 %

bl = 6.8 ps (FWHM)

n = 15.5 m



PHIN design achieved Nov. 2008

RF frequency [GHz] 2.9985 2.9985

RF power [MW] unloaded 13 13

beam energy [MeV] 5-6 5.3

beam current [A] 3.5 < 0.2*

number of bunches 1908 3000

bunch spacing [ps] 666.7 666.7

charge per bunch [nC] 2.3 < 0.1*

repetition rate [Hz] 5 0.8

bunch length FWHM [ps] < 10 < 10 ?

rms. energy spread [%] < 2 < 1

n. emittance [mm mrad] < 25 yes

vacuum pressure [mbar] < 2 x 10-10 < 4 x 109 *

* photocathode QE < 0.5% (factor 8-11) cathode prod. Dec. 2007 laser micropulse energy < 0.2 J (factor 2-3)

* NEG not yet activated

Beam parameter summary

ctf3 photoinjector konrad elsener for the photoinjector team

Documents