P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

LCLS - Accelerator System OverviewLCLS - Accelerator System Overview

Patrick Krejcikon behalf of the LCLS Team

Stanford Linear Accelerator Center

LCLSLCLS

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Ti:Sa laserRG Gun

Laser HeaterUpstream linacL0

Linac1

RF PhotoInjector 135 MeVx,y = 1mm mrad, q=1 nCz = 3ps, 0.05 % 0.05 %

Linac2

Linac3

BC1 chicane 250 MeVz = 0.63 ps

Existing SLAC structurewarm, copper linacS-band 2856 MHz120 Hz

X-band harmonic cavity

BC2 4.5 GeVz = 0.07 ps

UndulatorL =130 m

X-rays1.5 Å

LTU 14.1 GeVz = 0.07 ps, 0.01 % 0.01 %

1 kmLoLa transverse cavity

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Accelerator Issues in the SLAC Design

IssuesIssues Low emittance injectorLow emittance injector

Cold beam, low Cold beam, low 0.05 % 0.05 %

Bunch compressionBunch compressionCoherent Synchrotron Coherent Synchrotron RadiationRadiationLongitudinal space chargeLongitudinal space charge

Beam stabilityBeam stability

Design solutionsDesign solutions RF photoinjectorRF photoinjectorLaser heaterLaser heaterTwo magnetic chicanesTwo magnetic chicanesRF linearization with RF linearization with higher harmonic X-band higher harmonic X-band cavitycavityDiagnosticsDiagnosticsFast feedbackFast feedback

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Vrf Electron bunch S-band rf = -25º

energy

time

Electron bunch with higher energy tail

…tail begins to catch up

…fully compressed

additionalX-band rf = -160º

Bunch Compression Dynamics

Longitudinal tracking with litrack – P. Emma

Remove spike in distribution with addition of X-band

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Diagnostic challenges

MeasurementMeasurement Measurement of ultra-Measurement of ultra-short bunch profilesshort bunch profilesShot-by-shot Shot-by-shot measurement of bunch measurement of bunch lengthlengthBunch timing Bunch timing measurementmeasurement

DevicesDevices RF transverse deflecting RF transverse deflecting cavity “LOLA”cavity “LOLA”Terahertz coherent Terahertz coherent spectral power spectral power measurementmeasurementCoherent radiation Coherent radiation autocorrelationautocorrelationElectro-optic bunch Electro-optic bunch profilingprofiling

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Bunch Length Measurements with the RF Transverse Deflecting Cavity

yy

Asymmetric parabola indicates incoming tilt to beam

Y = A * (X - B)**2 + CA = 1.6696E-02 STD DEV = 1.3536E-03B = 28.23 STD DEV = 3.084C = 1328. STD DEV = 8.235RMS FIT ERROR = 23.63

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

****

***

**

**

*

****

********

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

E

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

-80 -40 0 40 80SBST LI29 1 PDES (S-29-1)

1.7

1.6

1.5

1.4

1.3

X103

E

MANUAL STEPPING. STEPS = 30

1-APR-03 20:21:16

Cavity on

Cavity off

Cavity on- 180°

Bunch length reconstructionMeasure streak at 3 different phases

z = 90 m

(Stre

ak s

ize)

2

0 180

2.4 m 30 MW

LoLa*

An S-band DLW structure with a TM11 transverse deflecting mode at 2856 MHz

*Loew, Larsen 1964

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Accelerator Issues in the SLAC Design

IssuesIssues Low emittance injector

Cold beam, low Cold beam, low 0.05 % 0.05 %

Bunch compressionBunch compressionCoherent Synchrotron Coherent Synchrotron RadiationRadiationLongitudinal space chargeLongitudinal space charge

Beam stability

Design solutionsDesign solutions RF photoinjectorLaser heaterLaser heaterTwo magnetic chicanesRF linearization with higher harmonic X-band cavityDiagnosticsDiagnosticsFast feedback

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Limitation from Coherent Synchrotron Radiationrrzz radiation coherentradiation coherent

Energy spread from CSR increases x

P. Emma

With CSR:With CSR: //00 14 14

no CSR:no CSR:

Limits compressionhypothetical 1 m bunch

CSR instabilityCSR instability amplifies noise in initial charge distribution

S. Heifets, S. Krinsky, G. Stupakov, S. Heifets, S. Krinsky, G. Stupakov, SLAC-PUB-9165, March 2002SLAC-PUB-9165, March 2002

33101066

Microbunching*

and further emittance growth

* First observed by M. Borland (ANL) in * First observed by M. Borland (ANL) in LCLS LCLS ElegantElegant tracking tracking

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Two-stage bunch compression approach – P. Emma

IssuesIssues At At low energieslow energies if bunch if bunch is compressed too much is compressed too much space chargespace charge spoils spoils emittanceemittanceAt At high energieshigh energies if bunch if bunch is compressed too hard is compressed too hard synchrotron radiationsynchrotron radiation adds large energy spreadadds large energy spread

Design solutionsDesign solutions Compress in two stagesCompress in two stagesLimit low energy Limit low energy compression so space compression so space charge not a limitcharge not a limitSecond compression to Second compression to final bunch length at final bunch length at higher energy, but with higher energy, but with weaker bends to limit weaker bends to limit synchrotron radiation.synchrotron radiation.

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Transition radiation is coherent at wavelengths longer than the bunch length,>(2)1/2 z

SLAC SPPS measurement: P. Muggli, M. Hogan

Limited by long wavelength cutoff and absorption resonances

0

0.4

0.8

1.2

1.6

-100 -50 0 50 100CombinedCTRInterferogramsSm

zz 9 9 mm

Diagnosing Coherent Radiation1. autocorrelation

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

m 190z

Diagnosing Coherent Radiation2. spectral power

Smooth Gaussian bunch spectrum from BC1

With 5% microbunching

• Measure bunch length

• Detect microbunching

Fixed BW detectorSignal prop. 1/z

Bunch length signal for RF feedback

- J. Wu

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

40 keV rms40 keV rms

‘‘Laser Heater’ for Landau DampingLaser Heater’ for Landau Damping

Z. Huang Z. Huang et al.et al.PR ST ABPR ST AB, , June 2004June 2004

Ti:Sa 800 nm 1.2 MWTi:Sa 800 nm 1.2 MW

Injector e- 135 MeVInjector e- 135 MeV

‘‘Laser heater’ Laser heater’ suggested by suggested by Saldin et al.Saldin et al.

heater heater ONON

0.01 %0.01 %

heater heater OFFOFF

0.1%0.1%

Final energy distribution:

Microbunch instability

Damped

IFELenergy modulation

chicaneenergy mixing

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Electro-Optical Sampling at SPPS Electro-Optical Sampling at SPPS – A. Cavalieri et al.– A. Cavalieri et al.

ee

Ti:Sapphire Ti:Sapphire laserlaser

Single-ShotSingle-Shot

<300 fs<300 fs

170 fs rms170 fs rmsTiming JitterTiming Jitter

Er

Line image camera

polarizer

analyzer

200 200 m thick ZnTe crystalm thick ZnTe crystal

Pol. Laser pulse

Electron bunch

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Energy and Bunch Length Feedback Loops

4 energy feedback loops2 bunch length feedback loops120 Hz nominal operation, <1 pulse delay

Feedback model (J. Wu)PID controller (proportional, integral, derivative)Cascade control for sequential loops (off-diagonal matrix elements)

L0 L1

DL1

DL1Spectr. BC1 BC2

L2 L3BSY 50B1 DL2

Vrf(L0)

Φrf(L2)Vrf(L1) Φrf(L3)E E E

Φrf(L2) zΦrf(L1) zE

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Bode Plot (E/E)

off

onEEEE

//

log20 10

P:0.2; I:0.5

P:0.2

on

off

/arg 0.0

/E EE E

Ø 3 different settings of the PID controller

ØIntegral term dominant

I:0.5

Energy feedback loop response - J. WuP. Emma

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Bode Plot (I/I)

on10

off

/20log

/I II I

P:0.2; I:0.5

P:0.2

on

off

/arg 0.0

/I II I

Ø 3 different settings of

the PID controller

ØIntegral term dominant

I:0.5

Bunch length feedback loop response - J. WuP. Emma

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Summary

Design optimized for emittance preservationMinimize disruption from strong self-fields of the bunchTwo-stage compressionLaser heater reduces instabilitiesDiagnostics and feedback integral part of designFuture expansion to multiple sase beamlinesNew possibilities include enhanced sase and ultra-short bunches!

P. Krejcik

LINAC 2004 – Lübeck, Germany pkr@slac.stanford.edu

August 16-20, 2004

Acknowledgements

R. AkreA. CavalieriE. BongD. DowellP. Emma Z. Huang C. Limborg-DupreyJ. WuAnd many others!

and thank you to the LINAC 2004 organization