Institute of Radiation Physics Jochen Teichert Forschungszentrum Dresden-Rossendorf Radiation...

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

Radiation Source 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 collaboration

The Superconducting RF Photoinjector at ELBE – First Operational Experience

Workshop on Sources of Polarized Electrons and High Brightness Electron BeamsOctober 1-3, 2008, Jefferson Lab, Newport News, VA


Radiation Source ELBEINTRODUCTION – MOTIVATION FOR SRF GUN

Int. FEL Community Radiation Source ELBE

High BrightnessHigh Average Current

CW OperationLow RF Power

Dissipation

250 kV thermionic GunCW operation

butlow brightness

low bunch charge

NC RF photogun highest brightness

butlow average current

high current gun for 4th generationlight sources ?

NEW CHALLANGESSC Cavity Design with Cathode InsertCavity Degradation during Operation

Choice of Photo cathode typeCoupling RF power in cavity & HOM effectsemittance growth compensation method


Radiation Source ELBEINTRODUCTION – HISTORY OF SRF GUN R&D

1988-91 proposal & first experimentA. Michalke, PhD Thesis, WUB-DIS 92-5Univ. Wuppertal, 1992

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

2002 first beam from a SRF gunD. Janssen et al., NIM-A, Vol. 507(2003)314


Radiation Source ELBEINTRODUCTION

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

Mode ELBE High Charge

final electron energy ≤ 9.5 MeV

RF frequency 1.3 GHz

operation mode CW

bunch charge 77 pC 1 nC

repetition rate 13 MHz 500 kHz

laser pulse (FWHM) 4 ps 15 ps

transverse rms emittance

1 mm mrad2.5 mm mrad

average current 1 mA 0.5 mA



LASER

NC Cs2Te photo cathode

heliumport

SC Nb3½ -cell cavity

e-

MAIN COMPONENTS

Liquid HeVessel

cathode cooling (77 K)& support system

photo cathodealignmentcavity

tuners

rf powercoupler

SRF Gun Cryomodule



DESIGN & PARAMETERS

Niobium Cavity

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

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

Ecathode = 20 MV/m (retracted cathode)

MAIN COMPONENTS

Results of the 4 vertical tests at DESY

HPR cleaning very difficultdemage produced

use of the cavity, sincefurther improvement not

expected


Radiation Source ELBECOMMISSIONING – FIRST COOL-DOWN

0 50 100 150 200 250 3001,2980G

1,2985G

1,2990G

1,2995G

1,3000G

1,3005G

fre

qu

en

cy [H

z]

temperature [K]

f=2.02MHz

first cool-down 1 – 2 August 2007



Quality factor and Gradient measurements

Eacc Epeak Eacc(TESLA) Eelectron

5.5 MV/m 15.5 MV/m 8 MV/m 2.5 MV

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

109

1010

-1

0

1

2

3

4

Q0 a

us

Ph

in &

Pd

iss

Gradient aus Phin [MV/m]

Do

sis

[m

Gy

/min

]

He consumption measurementand calibrated pick-up

constant He flowchange of electrical heater power

COMMISSIONING – RF TESTS



RF MEASUREMENTS

Measurement of RF properties:

COMMISSIONING – RF TESTS

• On-Axis Field distribution• He Pressure Sensitivity• Lorentz Force Detuning• Microphonics• Higher-Order Mode Excitation• Tuning System Performance• long term behavior of Q0 vs. Eacc curve for details see André Arnolds Poster


Radiation Source ELBECOMMISSIONING – RF TESTS

High-Power Processing of Cavity

Processing with pulsed RF for reduction of field emission in Sept. 08 High risk process – at the end of the measurement period

Improvement of acceleration gradientEacc = 5 -> 6.5 MV/m

Gun Operation with Ee = 3 MeV in next run(instead of 2 MeV before)


Radiation Source ELBECOMMISSIONING – UV LASER INSTALLATION

Laser pulse lateral:shaped with aperture to Ø 2.7 mm

circular flat top

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

Nd:YLF oscillatorNd:YLF regenerative amplifier

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



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

- Emittance measurement (slit mask)- C bend (E, E)- Cherenkov radiatior with optical beamline and streak camera

COMMISIONING - DIAGNOSTICS BEAMLINE


Radiation Source ELBEFIRST ELECTRON BEAM

Cu cathode

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

Beam spot on the first YAG screen in the BESSY diagnostics beamline

RF: Eacc = 5 MV/m f = 1300. 38327 MHz, 150 Hz bandwidth Pdiss = 6 WLaser: 263 nm, 100 kHz reprate 0.4 W power (4 µJ) temporal profile: 15 ps FWHM Gaussian lateral profile: 4 mm x 6mm spot, GaussianCathode: Cu, Q.E. ≈ 10-6

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


Radiation Source ELBECOMMISIONING - CATHODE TRANFER SYSTEM INSTALLATION

Transferchamber

Transportchamber

Lock

Cathode transfer rodlinear & rotation

Places for6 cathodes

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

at the SRF gun


Radiation Source ELBECs2Te PHOTO CATHODES

Photo cathode preparation lab at FZD

preparation process storage & recovery

May 08: First set of Cs2Te cathodes in the SRF gun

QE scan in SRF gun

QE = 10-3

bad“ vacuum in transfer chamberand during manupulation


Radiation Source ELBEBEAM PARAMETER MEASUREMENT

Schottky scan – optimum laser phase

screen DV02 (YAG) 1.9 m from gun exit, 2.7 m from cathode

-175°, σx = 300 µm

-150°, σx = 330 µm

-130°, σx = 610 µm

-115°, σx = 760 µm

-95°, σx = 330 µm

-65°, σx = 430 µm

+3°, σx = 1650 µm



Schottky scan – laser phase variation @ constant laser power

Laser temporal profile: 15 ps FWHM Gaussian spacial profile: 2.7 mm spot diameter flat top Faraday cup 0.6 m from gun exit, 1.4 m from cathode

space charge smoothing

Φlaser = 0°

slope determined bylaser pulse length

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



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

screen DV05same optical path as DV04

-160°, σx = 600 µm

energy energy spread

15 pC



Transverse Emittance – Solenoid scan

screen DV02 screen DV01

solenoid foremittance compensation, field precisely measured

•not suitable for space-charge dominated beams,•preliminary method as long as the analysis tools for the installed slit mask method are under development

Measurement: 5 MV/m gradient

2 MeV energylaser:

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

launch phase &

pulse energy variation

-160°20 pC

σx = 320 µm



Transverse Emittance – Solenoid scan

launch phase scan – search for optimum

- 160° Φlaser = 20°

bunch charge dependence


Radiation Source ELBESUMMARY

First Run of SRF Gun operation:about 100 h with Cu cathode, 400 h with Cs2Te Iav = 1 µA, total 15 C (diagnostic mode & radiation safety permission)

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)• 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 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



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

under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT-2003-506395) and the support of the German Federal

Ministry of Education and Research grant 05 ES4BR1/8.

THANK YOU FOR YOUR ATTENTION

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

to ACCEL and all the others supported and encouraged this project

Institute of Radiation Physics Jochen Teichert Forschungszentrum Dresden-Rossendorf Radiation...

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