commissioning the echo-seeding experiment echo-7 at nlcta

Commissioning the Echo-Seeding Experiment ECHO-7 at NLCTA

D. Xiang, E. Colby, M. Dunning, S. Gilevich, C. Hast, K. Jobe, D. McCormick, J. Nelson,T.O. Raubenheimer, K. Soong, G. Stupakov, Z. Szalata, D. Walz, S. Weathersby, M. Woodley

SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA

P-L. PernetEcole Polytechnique Federale de Lausanne, Lausanne, Switzerland

August-12-2010

Stephen Weathersby for the

ECHO-7 team

Outline

IntroductionPrinciple of HGHG FELThe principle of echo enabled HG (EEHG) Promises and challengesEcho-7 at NLCTAEcho-7 first resultsFuture plans

Introduction

Relates to electron bunch seeding by lasers for short-wavelength radiation generation

Introduction and preservation (echo effect) of fine longitudinal phase space correlations at high harmonics of a seeding laser

Enhancement of the demonstrated high gain harmonic generation (HGHG) seeding technique

Viable candidate for X-ray FEL seeding

4

Principle of High Gain Harmonic Generation (HGHG)

beam

modulator radiator

Energy modulation in the modulatorEnergy modulation converted to density

modulation

laser

5

Principles of HGHG FELHGHG characteristics

Up-conversion efficiency: characterized by bunching factor

k: wavenumber DE: laser modulation

sE : Intrinsic beam energy spread

•multiple stages required for X-ray FEL seeding•high power lasersLarge A means large beam energy spreadHigh peak current ~nI0Practical limit is

6

The principle of EEHG

beam

modulator 1 modulator 2 radiator

First laser to generate energy modulation in electron beamFirst strong chicane to split the phase spaceSecond laser to imprint certain correlationsSecond chicane to convert correlations into density modulation

laser 1seedlaser 2

HGHG

7

EEHG characteristicsUp-conversion efficiency for maximum bunching:

Nominal first laser modulation: DE1/sE ~ 3Bunching is independent of seed amplitude

Seed amplitude determines and final energy spreadLarge seed smaller , large final energy spreadNumerous small current density modulations

The principle of EEHG

8

EEHG FEL: promises and challenges Promises (in theory)o Remarkable up-frequency conversion efficiency allows the generation

of soft X-rays from UV seed lasers in a single stageo Peak currents are NOT significantly enhanced, which mitigates the

collective effects

Challenges

o Control & preservation of the phase space correlations

• CSR & ISR in the chicanes

• Quantum diffusion in the undulators from ISR

• Path length difference for particles with different betatron amplitude

• Unwanted x-z coupling from field errors, high order field components

9

World-wide interest in EEHG China J.H. Chen, et al, Operating the SDUV-FEL with the EEHG scheme,

Proceedings of FEL09, p410 (2009). France C. Evain, et al, Study of high harmonic generation at synchrotron SOLEIL

using echo enabling technique, Proceedings of IPAC10, p2308 (2010). Italy E. Allaria, et al, Feasibilities for single stage echo-enabled harmonic in

FERMI FEL-2, Proceedings of FEL09, p39 (2009). Switzerland S. Reiche, et al, Seeding option for the soft x-ray beamline of SWISSFLE,

Proceedings of FEL09, p51 (2009). UK I. Martin, et al, Short pulse options for the UK’s new light source project,

Proceedings of IPAC10, p2266 (2010). USA J. Corlett, et al, Design studies for a VUV-Soft x-ray FEL facility at LBNL,

Proceedings of IPAC10, p2639 (2010).

10

ECHO-7 at NLCTA

existing New ECHO beam line

Install X2 to boost beam from 60 MeV to 120 MeV Laser transport Construction of three undulators, three chicanes Add new or move existing quadrupoles, correctors, etc. New power supplies New diagnostics: OTRs, YAGs, cameras, movers, DAQ

ECHO-7 at NLCTA

Upstream view

12

ECHO-7 at NLCTA Milestoneso 03-2009: First planning meetingo 06-2009: LDRD fundedo 08-2009: Undulators orderedo 09-2009: BES Funding arrived / First chicane installed o 12-2009: 120 MeV beam achievedo 02-2010: First undulator installedo 04-2010: 795 nm laser-electron interaction achievedo 05-2010: 1590 nm laser-electron interaction achievedo 05-2010: First harmonic radiation observedo 7-2-2010: First echo signal

13

Milestoneso 03-2009: First planning meetingo 06-2009: LDRD fundedo 08-2009: Undulators orderedo 09-2009: BES Funding arrived / First chicane installed o 12-2009: 120 MeV beam achievedo 02-2010: First undulator installedo 04-2010: 795 nm laser-electron interaction achievedo 05-2010: 1590 nm laser-electron interaction achievedo 05-2010: First harmonic radiation observedo 7-2-2010: First echo signal

ECHO-7 at NLCTA

14


15


16

ECHO-7 at NLCTA Milestones-2-2010: First echo signal

17


18

ECHO-7 at NLCTA Milestones

X2 X-bandLength: 75 cmOperating gradient: 80 MV/mMax gradient: 100 MV/m

19


20

ECHO-7 at NLCTA Milestones U1, U2 STI Optronics U3 LBL with adjustable gap Pneumatically actuated OTR profile monitors

ECHO-7 at NLCTA Laser system overview Laser shorter than Beam

22

Parameters of ECHO-7 (July 2010)

Beam Energy 120 MeV

Bunch length 0.5 ps

Normalized Emittance 8 mm-mrad

Bunch charge 20-40 pCLaser wavelength in U1 795 nm NIR

Laser wavelength in U2 (seed) 1590 nm IR

Slice energy spread ~ 1 keV

Np x lu for U1 10 x 3.3 cm K=1.82

Np x lu for U2 10 x 5.5 cm K=2.09

Np x lu for U3 10 x 2 cm

Peak energy modulation in U1 and U2 10-40 keV

R56 for C1 and C2 1.0 ~ 9.0 mm

Radiation wavelength in radiator >318 nm UV

23

Spatial overlap

OTR1 OTR2Beam on OTR1

Laser on OTR1

Beam on OTR2

Laser on OTR2The spatial overlap is achieved by steering the laser to the same position as the electron beam on the OTR screens upstream and downstream of the undulators 107 attenuation

24

Temporal overlapphotodiode

The laser and undulator radiation are reflected out by the OTR screen and detected by a fast photodiode.

Scan delay stage to finely adjust the laser timing until the COTR enhancement is observed.

Beam off crest in X1

Beam on crest in X1

1.5 ps

5 ps

25

Radiator Spectrum Undulator radiation /OTR with UV window Transmission grating: 300 lines/mm Insertable bandpass filters 395 and 531 nm, 11 nm BW Glass lens and CCD camera

26

Wavelength calibration

(a)

(b) H2

1590 nm laser on

795 nm laser on

Incoherent undulator radiation

395 nm bandpass filter in

531 nm bandpass filter in

The radiation spectrum [350, 600] nm can be measured in a single shot

HGHG/EEHG predictions795 1590 Radiator (nm)

HGHG n=2 397 observed



EEHG n=-1 m=5 530 ?

EEHG n=-1 m=6 397 ?

Difficult to distinguish HGHG from EEHG for this range Somehow need to kill the 1590 nm HGHG contribution to

530 nm radiation 795 laser does not have harmonic content at 530 nm

795 1590 Radiator (nm)

HGHG n=2 397

HGHG n=3 530

HGHG n=4 397

EEHG n=-1 m=5 530 observed!

EEHG n=-1 m=6 397 ?

Experimental strategy

Establish the HGHG 1590 nm setup Reduce 1590 modulation strength until HGHG signal

disappears @ 530 and 397 nm Turn on 795 nm interaction and see if 530 nm reappears

29

First ECHO signal!

(a)

(b)

(c)

Radiation wavelength (nm)350 400 450 500 550 600

H2

H2

1590 nm laser onlyBut attenuated

No HGHG

795 nm laser onlyHGHG signal

Both lasers on with no 1590 nm HGHG

E-1,5

30

Separating EEHG from HGHG Theory predicts spectra shift differently for HGHG and EEHG in

the presence of an energy chirpHGHG

chirp

EEHG

31

ECHO signals when beam has an energy chirp

(a)

(b)

Radiation wavelength (nm)

H2

1590 nm laser on

795 nm laser on

HGHG

HGHG

HGHG + EEHG

E1 E2 E3350 400 450 500 550 600

H4 H3

H2

H4 H3H2

1590 nm seed laser on

795 nm laser on

Both lasers on

32

Separating EEHG from HGHG

For a chirp h ~ 33.4 m-1 the HGHG (H) and EEHG (E) simulation shows signals become distinct. (M) are ‘mystery echo peaks’

Such a chirp is applied by moving X2 phase by ~10 degrees

simulation

E1 E2 E3350 400 450 500 550 600

H4 H3H2Both lasers on

(b)

simulation

ECHO signals when beam has an energy chirp

H4 H3H2Both lasers on

Radiation wavelength vs. beam energy chirp

H2

E3

E2

Summary of first phase of Echo-7

Experimental verification of the EEHG schemeo About one year from inception to executiono Basic physics verified for lower harmonics n < 5

• Phase space correlations are preserved• Energy chirp prediction confirmed

First step towards one stage X-ray FEL seedingUpgrades and diagnostics will allow further

characterization of the radiation and realization of higher harmonics

H3H2Both lasers on

Future plans at NLCTA: T-Cavity Use transverse cavity to increase beam slice energy spread

After the transverse cavity, beam slice energy spread and transverse emittance both grow

A transverse cavity with V=100 kV deflection voltage is able to heat the slice energy spread to 10 keV and the transverse emittance only grows from 8 um to 8.5 um

H3H2Both lasers on

Future plans at NLCTA: THz radiation Narrow-band Beatwave THz emission

Beam current with (red) and without (blue) laser modulation

Radiation spectrum with (red) and without (blue) laser modulation

795 nm1549 nm

10 THz

Near future plans for Echo-7 at NLCTA08~09, 2010oCommission our new gun cathode and drive laseroRedo ECHO-3 to Echo-510, 2010oEcho-7oBeatwave THz radiation generationoStudies of Microbunching instabilities3~4, 2011o Use transverse cavity to increase beam slice energy spread

and redo the echo experiments5~6, 2011oECHO-15 and higher

commissioning the echo-seeding experiment echo-7 at nlcta

Documents

laser modulation se

eehg scheme

laser modulations

echoseeding experiment

high harmonics

modulatorenergy modulation

hghg scheme

hg eehg