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. Pernet Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland August Stephen Weathersby for the ECHO-7 team

Outline  Introduction  Principle of HGHG FEL  The principle of echo enabled HG (EEHG)  Promises and challenges  Echo-7 at NLCTA  Echo-7 first results  Future 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)  Energy modulation in the modulator  Energy modulation converted to density modulation laser

5 Principles of HGHG FEL HGHG characteristics  Up-conversion efficiency: characterized by bunching factor k : wavenumber   E : laser modulation  E : Intrinsic beam energy spread multiple stages required for X-ray FEL seeding high power lasers  Large A means large beam energy spread  High peak current ~nI 0  Practical limit is

6 The principle of EEHG  First laser to generate energy modulation in electron beam  First strong chicane to split the phase space  Second laser to imprint certain correlations  Second chicane to convert correlations into density modulation laser 1 seed laser 2 HGHG

7 EEHG characteristics  Up-conversion efficiency for maximum bunching:  Nominal first laser modulation:  E 1 /  E ~ 3  Bunching is independent of seed amplitude  Seed amplitude determines and final energy spread  Large seed  smaller, large final energy spread  Numerous 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 stage o 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  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal

13  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal ECHO-7 at NLCTA

14 ECHO-7 at NLCTA  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal

15 ECHO-7 at NLCTA  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal

16 ECHO-7 at NLCTA  Milestones : First echo signal

17 ECHO-7 at NLCTA  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal

18 ECHO-7 at NLCTA  Milestones X2 X-band Length: 75 cm Operating gradient: 80 MV/m Max gradient: 100 MV/m

19 ECHO-7 at NLCTA  Milestones o : First planning meeting o : LDRD funded o : Undulators ordered o : BES Funding arrived / First chicane installed o : 120 MeV beam achieved o : First undulator installed o : 795 nm laser-electron interaction achieved o : 1590 nm laser-electron interaction achieved o : First harmonic radiation observed o : First echo signal

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 Energy120 MeV Bunch length0.5 ps Normalized Emittance8 mm-mrad Bunch charge20-40 pC Laser wavelength in U1795 nmNIR Laser wavelength in U2 (seed)1590 nmIR Slice energy spread~ 1 keV N p x u for U1 10 x 3.3 cmK=1.82 N p x u for U2 10 x 5.5 cmK=2.09 N p x u for U3 10 x 2 cm Peak energy modulation in U1 and U keV R 56 for C1 and C21.0 ~ 9.0 mm Radiation wavelength in radiator>318 nmUV

23 Spatial overlap OTR1OTR2 Beam on OTR1 Laser on OTR1 Beam on OTR2 Laser on OTR2 The 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 10 7 attenuation

24 Temporal overlap photodiode  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) H 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 predictions Radiator (nm) HGHGn=2397observed HGHGn=3530observed HGHGn=4397observed EEHGn=-1m=5530? EEHGn=-1m=6397?  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

Radiator (nm) HGHGn=2397 HGHGn=3530 HGHGn=4397 EEHGn=-1m=5530observed! EEHGn=-1m=6397? Experimental strategy  Establish the HGHG 1590 nm setup  Reduce 1590 modulation strength until HGHG signal 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) H nm laser only But attenuated No HGHG 795 nm laser only HGHG 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 chirp HGHG chirp EEHG

31 ECHO signals when beam has an energy chirp (a) (b) Radiation wavelength (nm) H nm laser on 795 nm laser on HGHG HGHG + EEHG E1 E2 E H4 H3 H2 H4H3H 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 E H4H3H2 Both lasers on (b) simulation ECHO signals when beam has an energy chirp

H4H3H2 Both lasers on Radiation wavelength vs. beam energy chirp H2 E3 E2

Summary of first phase of Echo-7  Experimental verification of the EEHG scheme o About one year from inception to execution o 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 seeding  Upgrades and diagnostics will allow further characterization of the radiation and realization of higher harmonics

H3H2 Both 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

H3H2 Both 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 nm 1549 nm 10 THz

Near future plans for Echo-7 at NLCTA  08~09, 2010 o Commission our new gun cathode and drive laser o Redo ECHO-3 to Echo-5  10, 2010 o Echo-7 o Beatwave THz radiation generation o Studies of Microbunching instabilities  3~4, 2011 o Use transverse cavity to increase beam slice energy spread and redo the echo experiments  5~6, 2011 o ECHO-15 and higher