High Rep Rate Guns: FZD Superconducting RF … of Radiation Physics Jochen Teichert Forschungszentrum Dresden-Rossendorf Radiation Source ELBE J. Teichert, A. Arnold, H. Büttig, D

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,K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, G. Staats, F. Staufenbiel,

H. Tietze, R. Xiang, P. Kneisel, B. v. d. Horst, A. Matheisen, J. StephanT. Kamps, J. Rudolph, M. Schenk, G. Klemz, I. Will, V. Volkov

High Rep Rate Guns:FZD Superconducting RF Photogun

FLS 2010 Workshop, SLAC, March, 1-5, 2010


Radiation Source ELBEINTRODUCTION – HISTORY OF SRF GUN R&D

68 7

1 2 3 4

5

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

2002 first beam from a SCRF gun @ FZDD. Janssen et al., NIM-A, Vol. 507(2003)314

since 2004: Development of the 3½-Cell SRF Photoinjector for ELBE A. Arnold et al., NIM-A, Vol. 577(2006)440


Radiation Source ELBECOMMISSIONING – FIRST COOL-DOWN

0 50 100 150 200 250 3001,2980G

1,2985G

1,2990G

1,2995G

1,3000G

1,3005G

frequ

ency

[Hz]

temperature [K]

∆f=2.02MHz

first cool-down 1 – 2 August 2007


Radiation Source ELBECOMMISSIONING - FIRST ELECTRON BEAM

Cu cathode

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

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

Cathode: Cu, Q.E. ≈ 10-6

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

first beam of the 3½ cell SRF gun on November 12th, 2007


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 mrad 2.5 mm

mrad

average current 1 mA 0.5 mA



Design for the SRF-Gun @ ELBE• CW + high rep rate - 500 kHz, 13 MHz and higher• medium average current 1 – 2 mA (< 10 mA)• high energy (stand alone) - 3½ cells• low - high bunch charge 80pC – 1 nC• low transverse emittance 1 – 3 mm mrad• normal-conducting, lqN2-cooled, exchangeable,

semi-conductor photo cathode• highly compatible with ELBE cryomodule(1.3 GHz cavity, 10 kW coupler, He & N2 support, etc.)

Application @ ELBE• high peak-current operation for FELs with (13 MHz, 80 pC)• high current (1 mA) @ low rep rate (<1 MHz) -> high charge

pulsed secondary particle beams: neutrons, positronswith ToF measurements

• low emittance @ medium charge (100 pC) for short pulsesTHz-radiationx-rays by inverse Compton backscattering



LASER

NC Cs2Tephoto 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



parameter present cavity new “high gradient cavity”measured ´08 ELBE high charge ELBE high charge

final electron energy 2.1 MeV 3 MeV ≤9.5 MeV

peak field 13.5 MV/m 18 MV/m 50 MV/m

laser rep. rate 1 – 125 kHz 13 MHz 2 – 250 kHz 13 MHz ≤500 kHz

laser pulse length (FWHM)

15 ps 4 ps 15 ps 4 ps 15 ps

laser spot size 2.7 mm 5.2 mm 5.2 mm 2 mm 5 mm

bunch charge ≤ 200 pC 77 pC 400 pC 77 pC 1 nC

max. aver. Current 1 µA 1 mA 100 µA 1 mA 0.5 mA

peak current 13 A 20 A 26 A 20 A 67 A

transverse. norm. emittance (rms)

3 1 mm mrad@ 80 pC

2 mm mrad 7.5 mm mrad 1 mm mrad 2.5 mm mrad

SRF Gun Parameter

MEASUREMENT & OPERATION PARAMETERS



0.0 10.0M 20.0M 30.0M 40.0M 50.0M

1E9

1E10

Q 0

Epeak in V/m

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

achieved peak axis fields of all 4 vertical test benches Tests in thevertical cryostat(1.8 K) at DESYin 2007

3½ CELL CAVITY

HPR cleaning very difficult, surface damagedafter 4 vertical test at DESY improvement not expected

cavity used as it was, assembly continued

Treatment and test of the cavity



Helium consumption measurement

3½ CELL CAVITY

Cavity performance in the gun

2.7peak

acc

EE

=

• maximum achievable field only 1/3 of the designed value of Epeak=50 MV/m,• measured Q0 is 10 times lower than in all vertical tests,• gradient is limited by field emission• no Q degradation found since the 1st measurement in 2007,• Improvement by (9th test) high power processing (HPP) results 3 MeV operation• After warming-up or cathode exchange the HPP must be repeated


Radiation Source ELBE3½ CELL CAVITY

Energy and energy spread @ 5 pC (w/o space charge)



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

30,6

30,9

31,2

31,5

pres

sure

[mBa

r]

time [hh:mm]

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

1,30038102G

1,30038108G

1,30038114G

1,30038120G

1,30038126G

1,30038132G

f 0 [H

z]

RF MEASUREMENTS

He pressure effect on cavity frequency

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

1300381020

1300381040

1300381060

1300381080

1300381100

1300381120

1300381140

1300381160

1300381180

1300381200

∆=232,61337 Hz/mBar

f0 [Hz]

P [mBar]

Messwerte f0 vs. P lineare Regression

Lorentz force detuning

SRF-gun ~230 Hz/mbar ELBE module ~35 Hz/mbar

3½ CELL CAVITY

SRF-gun K= 0.69 Hz/(MV/m)²ELBE module K = 0.25 Hz/(MV/m)²(with respect to peak fields)


Radiation Source ELBE3½ CELL CAVITY

New “High Gradient” Cavity

old design new design

Improvements• higher stiffness of the half-cell back wall

microphonics, Lorentz force detuning• larger opening in choke and partly in half-cell

better HPR cleaning• new pick-up antenna design, etc.

simpler clean-room assembly



New “High Gradient” Cavity

3½ CELL CAVITY

Fabricated in collaborationwith JLab, thanks to P. Kneisel

standardRRR 300Nb cavity

Large grainNb cavity

now: warm tuning @ JLabnext: warm rf measurements @ FZD

cleaning & test @ JLab



Photo cathode preparation equipment at FZD

Ø10 mm Cs2Tecone forpositioning &thermal contact

pressure springbayonet fixing

Photo Cathode Transfer System

Cs2Te PHOTO CATHODES



Transferchamber

Transportchamber

Lock

Cathode transfer rodlinear & rotation

Places for6 cathodes

Use of semiconductor photo cathodes likeCs2Te requires a UHV exchange systemwith <109 mbar

• Cool PC exchange works • Change of PC needs ~30 min• Docking of transport chamberneeds 1 maintenance shift+ 1 week backing (duringELBE operation)

Photo Cathode Transfer System

Cs2Te PHOTO CATHODES


Radiation Source ELBEUV LASER SYSTEM

UV CW Laser system delivered by MBILaser upgrade 2010

(0.5 W @ 262 nm)

Two oscillators13 MHz:

Nd:glass oscillator (26 mHz)3 ps FWHM Gaussian

500, 250, 125 kHz:Nd:YLF oscillator (26 mHz)

14 ps FWHM Gaussian

one amplifierNd:YLF multipass amplifier

10-20 W

two UV converterstwo-stage frequency

converters (LBO, BBO)existing ≤250 kHz laserwith Nd:YLF regenerativeamplifier


Radiation Source ELBEUV LASER SYSTEM

Upgrade of the laser beam line & virtual cathode

remote-controlled laser spot size setting(telescope & aperture)

Measurement of laser profile, position, andpower on the virtual cathode screen



diagnostics beamline designed and built by HZB (BESSY) Berlin

- Laser input port, Solenoid- Current & Charge (Faraday-cup & ICTs) - Transverse Emittance (slit mask, solenoid scan)- Energy and ∆E (C-bent)- Bunch length (Cherenkov radiator with optical

beamline and streak camera,electro-optical sampling

BEAM PARAMETER MEASUREMENT - DIAGNOSTICS BEAMLINE


Radiation Source ELBEELBE INJECTION

Installation of electron beamline to ELBE was finished in winter shutdown 2009/10

First accelerated SRF gun beam at ELBE on Febr. 5, 2010


Radiation Source ELBEELBE INJECTION

5 MeV energy increaseCompared to thermionicinjector3 MeV from SRF gun,2 MeV from on-crestinjection


Radiation Source ELBESUMMARY

In 2009• Upgrade of the cathode transfer system: sufficient vacuum, backing duringELBE operation

• Installation of the beam line to ELBE• Commissioning of the Cherenkov station for bunch length measurements• Spectrometer for slice emittance measurements delivered• Design upgrade and fabrication of two new “high gradient” cavities

Outstanding and planned for 2010• Demonstration of ELBE injection• Preparation and Test of the new cavities at JLab• Demonstration of high-current operation with 13 MHz laser & PC >1% QE• Systematic experimental studies of HOM excitation in the gun• Measurements & Optimization to find the bunch charge limit at 3 MeV• First ELBE user beam with SRF gun



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

under the FP6 programme 2004-08 (CARE, contract number RII3-CT-2003-506395) and the FP7 programme since 2009 (EuCARD, contract number 227579) as well as 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 RI, JLab, and all the others supported and encouraged this project

Documents

High Rep Rate Guns: FZD Superconducting RF … of Radiation Physics Jochen Teichert Forschungszentrum Dresden-Rossendorf Radiation Source ELBE J. Teichert, A. Arnold, H. Büttig, D