Photo Injector Test Facility Zeuthen RF Gun Experience at ... · Photo Injector Test Facility Zeuthen RF gun conditioning strategy ... drive laser experience at PITZ: ... SLAC2006-PITZoverviewFS3.ppt

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 1

P I T ZPhoto Injector Test

Facility Zeuthen

RF Gun Experience at PITZ/FLASH

Content:• commissioning the RF gun for FLASH at PITZ:

- old setup, emittance measurement technique- optimization strategy, results

• developing the electron source for the XFEL:- strategy, new setup- conditioning (strategy)

• the water system at PITZ

part A: overview

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 2

P I T ZPhoto Injector Test

Facility ZeuthenCollaboration and Layout

BESSY Berlin, CCLRC Daresbury,DESY (HH + Z), INFN Frascati,INFN Milano, INR Troitsk,INRNE Sofia, LAL Orsay,MBI Berlin, TU Darmstadt,U Hamburg, YERPHI Yerevan

Institutes collaborating at PITZ:

(1.3 GHz)

PITZ setup in 2003:

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 3

P I T ZPhoto Injector Test

Facility Zeuthen

beamlet size is measuredfor 3 slit positions: { }1,0,1

7.0 22

−∈

⋅+=

nnYy screen

yscreen

n σ

Transverse EmittanceMeasurement Technique

beam spot at screen 2single slitpositions

beamlets at screen 3

Single Slit Scan Technique 222 xxxxnx ′−′= βγε

Now: we use 7-11 different slit positions; separation of slits is ~100µm (depending on beam size)

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 4

P I T ZPhoto Injector Test

Facility ZeuthenInfluence of vacuum mirror

improvement: > 0.5 mm mrad

1 nC, D = 1.2 mm

• status in Sept. 2003: min. emittance ≈ 3 mm mrad• problem: misalignment of laser vacuum mirror port• improvement: steer beam away from vacuum mirror

steerer A

vacuum mirror

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 5

P I T ZPhoto Injector Test

Facility Zeuthen

• important parameters: longitudinal and transverse laser shape, launch phase, solenoid focussing, magnetic field on cathode

• longitudinal and transverse laser shape changes required iterative re-adjustment of all laser parameters slow change rate (improvement: now laser parameters are less dependent)

• solenoid and launch are easy changeable high change rate• Need to define unique measurement conditions in order to compare

measurements from different shift crews

• ~300 emittance measurements have been done for the FLASH gun and ~ 420 measurements for the successor gun without booster cavity.

Optimizing strategy

emittance optimization at PITZtemporal laser profileGaussian → Flat-Top

RF gun gradient42MV/m → 45MV/m

laser transverse profile and spot size on the cathodeemittance scan

(RF Phase, Imain, Ibuck=0)bucking solenoid

tuning (Ibuck)

emittance scan (RF Phase, Imain),

Ibuck = a * Imaina = 0.074847

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 6

P I T ZPhoto Injector Test

Facility Zeuthen

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

0 10 20 30 40 50Ibuck, A

norm

. em

ittan

ce /

mm

mra

d

ExEySQRT(Ex*Ey)ASTRA sim.

Φ = Φm – 5°Imain = 305 A

Results of experimental optimization

Start-up requirement of FLASH clearly fulfilled !

FLASH (30 nm)

FLASH (6 nm)

main solenoid

bucking solenoid

FLASH gun: Successor gun:• improved transverse laser profile,• increased gun gradient

(momentum 10% higher)

Q = 1 nC

0,8

1,2

1,6

2,0

2,4

2,8

3,2

320 322 324 326 328 330Imain, A

norm

. em

ittan

ce /

mm

mra

d ExEySQRT(Ex*Ey)

Φ = Φm

Ibuck = Imain * 0.075

FLASH (6 nm)

XFEL

XFEL

FLASH (30 nm)

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 7

P I T ZPhoto Injector Test

Facility ZeuthenHow to develop the XFEL injector

• to improve emittance from the gun:– increase acc. gradient at cathode (40 60 MV/m)– reduce rise/fall time of laser pulse to ≤ 2 ps, operate with ~20 ps

FWHM (slice emittance of larger part of bunch small enough + measured projected properties closer to slice properties)

• to conserve small emittance to higher beam energy:– install booster cavity and high energy diagnostics– study emittance evolution after booster and do experimental

optimization of injector parameters (laser, gun, magnets, booster)• side constraints:

– test setup should be as close as possible to real setup (FLASH gun charc. @PITZ without booster, now booster position given byFLASH, different laser systems (stability of temporal pulse shaper ↔user operation))

– remaining extrapolation to be done with simulations– supply spare components, test new developments (laser, cathode)– study XFEL upgrade machine parameter space (bunch, rep rate)

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 8

P I T ZPhoto Injector Test

Facility Zeuthen

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8 9 10z / m

Xrms (CDS14) / mm

EmX (CDS14) / um

Xrms (no booster) / mm

EmX (no booster) / um

matchingcondition

(M. Ferrario)

CDS booster

diagnostics section

µm

µm

Emittance Conservation Principleem

ittan

ce a

nd b

eam

size

distance from photo cathode (m)

60MV/m, 20ps FWHM, 2ps rise/fall time

⇒ goals can be met, do experimental optimization.

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 9

P I T ZPhoto Injector Test

Facility Zeuthen

~ PITZ1(≠ PITZ1)

new

gunboosterlongitudinalphase space

masks

transverseemittance

quads

rf deflector

Preliminary PITZ2 Layout

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 10

P I T ZPhoto Injector Test

Facility ZeuthenRF gun conditioning strategy

• particle free cleaning and baking of vacuum components helps to reduce conditioning time

• large part of total conditioning time often spent at low peak power(multipacting vacuum) and at high average power (time to stabilize cooling water)

• sweeping solenoid current sometimes helps to overcome conditioning threshold (multipacting) and is needed to have fully conditioned cavity cleaning of full cavity

• conditioning just below vacuum interlock threshold is most efficient, setting of vacuum threshold is important parameter for conditioning time and risk for major breakdowns (PITZ gun3: 10^-8 mbar, BESSY gun: 10^-7 mbar)

• quick photomultiplier interlock can limit RF breakdown • to overcome detuning of cavity after interlock at high average power

RF frequency can be tuned to current cavity resonance tuning was done by hand for BESSY gun needs manpower

• automatic conditioning procedures can run at night and during weekends without manpower

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 11

P I T ZPhoto Injector Test

Facility ZeuthenGun3 RF conditioning results

Gun3 was conditioned to full FLASH specification:– up to 3.5 MW RF peak power– up to 900 mirco seconds RF pulse length– RF pulse repetition rate of 10 Hz

31.5 kW average power, 0.9 % duty cycle

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 12

P I T ZPhoto Injector Test

Facility ZeuthenWater system at PITZ

• stability requirement:± 0.05 °K achieved !

• problems: – radiation hardness of mixing valves

(spare parts)– stability of control algorithm for different

operation modes (different control parameter sets)

– cold water pressure must always be larger than warm water pressure (depending on mixing valve positionand overall hydraulic system)

• relatively quick reaction on changing cooling requirements (interlocks) by mixing cold and warm water close to the gun,c/w water reservoirs

800 µs,

5 Hz,

~ 3 MW

Not to scale !!

F. Stephan, DESY, LCLS Injector Commissioning Workshop, Oct. 9th+11th, 2006 13

P I T ZPhoto Injector Test

Facility ZeuthenNext talks• Jürgen Bähr: drive laser experience at PITZ:

– photo cathode laser system– laser beam line to photo cathode

• Mikhail Krasilnikov: RF-Gun beam based alignment (BBA) at PITZ/FLASH:– BBA of laser on cathode– BBA of gun solenoid

• Juliane Rönsch: longitudinal phase space:– streak camera readout– bunch length measurements– longitudinal phase space measurements