Post on 24-Feb-2016
description
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
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
15
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
16
ECHO-7 at NLCTA Milestones-2-2010: First echo signal
17
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
18
ECHO-7 at NLCTA Milestones
X2 X-bandLength: 75 cmOperating gradient: 80 MV/mMax gradient: 100 MV/m
19
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
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
HGHG n=3 530 observed
HGHG n=4 397 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