Initial Commissioning Experience with the Initial ...INTRODUCTION – HISTORY OF SRF GUN R&D...

Radiation Source ELBE

Initial Commissioning Experience with the

J Teichert A Arnold H Büttig D Janssen M Justus U Lehnert P Michel

Initial Commissioning Experience with the Superconducting RF Photoinjector at ELBE

J. Teichert, A. Arnold, H. Büttig, D. Janssen, M. Justus, U. Lehnert, P. Michel,P. Murcek, A. Schamlott, C. Schneider, R. Schurig, F. Staufenbiel, R. Xiang,

T. Kamps, J. Rudolph, M. Schenk, G. Klemz, I. Willfor the BESSY DESY FZD MBI collaborationfor the BESSY-DESY-FZD-MBI collaboration

Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf

30th International Free Electron Laser Conference, Gyeongju, Korea, 2008

Radiation Source ELBEINTRODUCTION – MOTIVATION FOR SRF GUN

Int. FEL Community Radiation Source ELBERadiation Source ELBEthermionic GunCW operation

but

NC RF photogunhighest brightness

but butlow brightness

low bunch charge

low average current

High BrightnessHigh Average CurrentNEW CHALLANGESHigh Average Current

CW OperationLow RF Power

Di i tihigh current gun for

SC Cavity Design with Cathode InsertCavity Degradation during Operation

Choice of Photo cathode typeDissipation4th generation

light sources ?Coupling RF power in cavity & HOM effects

emittance growth compensation method


Radiation Source ELBEINTRODUCTION – HISTORY OF SRF GUN R&D

1988-91 proposal & first experiment

1 2 3 4

A. Michalke, PhD Thesis, WUB-DIS 92-5Univ. Wuppertal, 1992

2002 first beam from a SRF gun

68 7 5

D. Janssen et al., NIM-A, Vol. 507(2003)314


since 2004 ELBE SRF PhotoinjectorA. Arnold et al., NIM-A, Vol. 577(2006)440

Radiation Source ELBEINTRODUCTION

ELBE Superconducting RF PhotoinjectorELBE Superconducting RF Photoinjector• New Injector for the ELBE SC Linac• Test Bench for SRF Gun R&D

Mode ELBE High Charge

fi l l t ≤ 9 5 M Vfinal electron energy ≤ 9.5 MeV

RF frequency 1.3 GHz

operation mode CW

bunch charge 77 pC 1 nCbunch charge 77 pC 1 nC

repetition rate 13 MHz 500 kHz

laser pulse (FWHM) 4 ps 15 ps

transverse rms 1 mm mrad 2.5 mm


emittance 1 mm mrad mrad

average current 1 mA 0.5 mA


h li

MAIN COMPONENTS

Li id H SRF Gun Cryomoduleheliumport

Liquid HeVessel

photo cathode

y

alignmentcavitytuners

LASER

e- cathode cooling (77 K)& t t

NC Cs2TeSC Nb

& support system

rf power


photo cathode3½ -cell cavityp

coupler


Niobium Cavity

MAIN COMPONENTS

DESIGN & PARAMETERS

yNb RRR 300 cavity –design valuesEacc= 25 MV/m in TESLA cells, Q0=1x1010

110 mT maximum magnetic surface field110 mT maximum magnetic surface fieldEpeak (TESLA cells) = 50 MV/mEpeak (half-cell) = 30 MV/mEcathode = 20 MV/m (retreated cathode)

achieved peak axis fields of all 4 vertical test benches

Results of the 4 vertical tests at DESY

1E10

Q0

HPR cleaning very difficultdemage produced

1E9 V-Test 1 V-Test 2 V-Test 3V-Test 4all 4 tests limited by field emission

use of the cavity, sincefurther improvement not

expected


0.0 10.0M 20.0M 30.0M 40.0M 50.0M

Epeak in V/m

V Test 4y p

Radiation Source ELBECOMMISSIONING – FIRST COOL-DOWN

first cool-down 1 – 2 August 2007

1,2995G

1,3000G

1,3005G

frequ

ency

[Hz]

1,2985G

1,2990G

Δf=2.02MHz


0 50 100 150 200 250 3001,2980G

temperature [K]

Radiation Source ELBECOMMISSIONING – RF TESTS

Quality factor and Gradient measurements1010 4

2

3

Pdis

s

min

]

109

0

1

Q0 a

us P

hin

&

Dos

is [m

Gy/

1,0M 2,0M 3,0M 4,0M 5,0M 6,0M 7,0M108 -1

0

Gradient aus Phin [MV/m]

Eacc Epeak Eacc(TESLA) Eelectron

5 5 MV/m 15 5 MV/m 8 MV/m 2 5 MV

He consumption measurementand calibrated pick-up

constant He flowh f l t i l h t


5.5 MV/m 15.5 MV/m 8 MV/m 2.5 MVchange of electrical heater power


He pressure effect on cavity frequency

COMMISSIONING – RF TESTS

31,2

31,5pr

essu

re [m

Bar

]SRF Gun: ~ 230 Hz / 1mbarELBE Linac: ~ 35Hz / 1mbar

1,30038120G

1,30038126G

1,30038132G

f 0 [H

z]

RF MEASUREMENTS

p y q y

1300381140

1300381160

1300381180

1300381200 Messwerte f0 vs. P lineare Regression

09:36 10:48 12:00 13:12 14:24 15:36

30,6

30,9

time [hh:mm]

1,30038102G

1,30038108G

1,30038114G

1300381020

1300381040

1300381060

1300381080

1300381100

1300381120

Δ=232,61337 Hz/mBar

f0 [Hz]

P [mBar]time [hh:mm]

30,6 30,7 30,8 30,9 31,0 31,1 31,2 31,31300381000

P [mBar]

Lorentz force detuning


Radiation Source ELBECOMMISSIONING – UV LASER INSTALLATION

500 kHz Laser system developed by MBI262 nm CW laser mit 0 5 W /UV)262 nm CW laser mit 0.5 W /UV)

Nd:YLF oscillatorNd:YLF regenerative amplifier

two-stage frequ. conv. (LBO, BBO)15 ps FWHM Gaussian15 ps FWHM Gaussian

Laser pulse lateral:shaped with aperture to Ø 2 7 mmshaped with aperture to Ø 2.7 mm


Radiation Source ELBECOMMISIONING - DIAGNOSTICS BEAMLINE

ELBE shut-down, Oct. 15 – 26, 2007Installation of BESSY diagnostics beamline

- Emittance measurement (slit mask)- C bend (E, ΔE)

Ch k di ti ith ti l- Cherenkov radiatior with opticalbeamline and streak camera


Radiation Source ELBEFIRST ELECTRON BEAM

First beam of the 3½ cell superconducting rf photo gun on November 12th, 2007

RF: Eacc = 5 MV/mf = 1300. 38327 MHz, 150 Hz bandwidthPdiss = 6 W

Laser: 263 nm, 100 kHz reprate0 4 W power (4 µJ)

Cu cathode

Beam spot on the first YAG screenin the BESSY diagnostics beamline

0.4 W power (4 µJ)temporal profile: 15 ps FWHM Gaussianlateral profile: 4 mm x 6mm spot, Gaussian

Cathode: Cu, Q.E. ≈ 10-6

El b 2 0 MV


Electron beam: 2.0 MV energy 50 nA average current,0.5 pC bunch charge

Radiation Source ELBECOMMISIONING - CATHODE TRANFER SYSTEM INSTALLATION

L kLock Places for6 cathodes

installation in the shut-downsof ELBE in Jan + March 08

Transportchamber

of ELBE in Jan. + March 08at the SRF gun

Transferchamber

Cathode transfer rodlinear & rotation


Radiation Source ELBECs2Te PHOTO CATHODES

Photo cathode preparation lab at FZD May 08: First set of Cs2TeMay 08: First set of Cs2Tecathodes in the SRF gun

QE scan in SRF gun

preparation process storage & recovery

QE = 10-3

bad“ vacuum in transfer chamberand during manupulation


Radiation Source ELBEBEAM PARAMETER MEASUREMENT

Schottky scan – laser phase variation @ constant laser power

Laser pulse rep. Rate250, 125, 50 kHz: user operation1, 2, 5 kHz: diagnostic

space charge smoothing

Φlaser = 0°slope determined by

laser pulse length

Laser temporal profile: 15 ps FWHM Gaussianspacial profile: 3 mm spot diameter flat top

Faraday cup 0.6 m from gun exit,

p g g


Faraday cup 0.6 m from gun exit,1.4 m from cathode


Schottky scan – energy & energy spread screen DV04 (YAG)4.4 m from cathode

-160°,σx = 600 µm

screen DV05same optical path as DV04

energy energy spread


15 pC


Transverse Emittance – Solenoid scan •not suitable for space-charge dominated beams,•preliminary method as long as the analysistools for the installed slit mask method are under development

screen DV02 screen DV01

solenoid foremittance compensation, field precisely measured

Measurement:5 MV/m gradient

2 M V2 MeV energylaser:

temporal:15 ps FWHM Gaussianlateral: 2.7 mm diam. sharp edges

-160°20 pC

launch phase &pulse energy variation


σx = 320 µm


Transverse Emittance – Solenoid scan

launch phase scan – search for optimum bunch charge dependence

- 160° Φlaser = 20°


Radiation Source ELBESUMMARY

Problems during commissioning:• Cavity cleaning and low gradient• wrong cavity π-mode frequency at 2 K (will be corrected in shut-down)

high level of microphonics due to membrane pumps (solved)• high level of microphonics due to membrane pumps (solved)• tuners have hysteresis (will be repaired in shut-down)• insufficient vacuum in cathode transfer system (improved in shut-down)

Answers to the „big“ questions:• basic principle (NC photo cathode) works well• no limits found, results agree with predictions• high current operation: answer will be given in the first run in 2009• high current operation: answer will be given in the first run in 2009• high gradient and brightness: needs an improved cavity

Future:• Oct.- Jan. 09: correction of π-mode frequency• 2009: connection to ELBE, run with high current • fabrication of two improved cavities, funded by BMBF, replacement in 2010


Radiation Source ELBETHANK YOU FOR YOUR ATTENTION

Thanks to the ELBE crewThanks to the ELBE crew, the technical staff of BESSY, DESY and MBI,

to ACCEL and all the others supported and encouraged this project

AcknowledgementsWe acknowledge the support of the European Community-Research Infrastructure Activity

under the FP6 “Structuring the European Research Area” programme


F g E p p g mm(CARE, contract number RII3-CT-2003-506395) and the support of the German Federal

Ministry of Education and Research grant 05 ES4BR1/8.

Initial Commissioning Experience with the Initial ...INTRODUCTION – HISTORY OF SRF GUN R&D...

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