High-brightness electron beams with tunable … electron beams with tunable modulation Timur Shaftan ... Helium Neon 543, 594, 612, ... Terahertz Diagnostics The

Brookhaven Science Associates

U.S. Department of Energy

High-brightness electronbeams with tunable

modulation

Timur Shaftan (BNL)

The Physics and Applications of High Brightness Electron Beams 2005, Erice, Italy, 2005



Outline

• Modulated beams, “tools” for longitudinal phase space

• Modulation generated by collective effects! Longitudinal Space Charge effect

! Coherent Synchrotron Radiation effect

! Cure: LCLS “laser-heater”

• Creating modulated beams for radiation sources! Seeded FEL schemes/Tunability

! Study of modulated bunch with an energy chirp

! Beams modulated at photocathode " THz generation

! Self-seeded schemes

• Conclusion



Longitudinal phase space of modulated beam

Energy

Distance

Peak current

Distance

Bunch length

Local/Globalenergy spread

Local chirp

Global chirp

Modulationperiod



“Tools”Dispersion in:

An energy modulated beam

Accelerator tank

Chirp in:

!

"#

h

E

( )( )!

!

"

#

cos

sin2

EE

Eh

inRF$+

$=

"E

h~10 m-1 for S-band

in

h!"

# !$=2

h~103…104 m-1

LBchicane

$

( )BLLR !+" 3/22

2

56# ; R56~0.1 m

Dispersion section

232

056 )/(3/4 BRdBR !" ; R56~10-3 m

Undulator

!pNR 256"

Np

; R56~10-4 m

for medium energy

Storagering ! "= dsR #$ /

56 ; R56 …~1 m

d

"L

B0

%

#

z



Modulation driven by collective effects

Longitudinal Space ChargeLongitudinal Space Charge

• LSC drives small density clusters into energy modulation

from: Z.Huang et al., FEL-2002

density modulation

energy modulationR56

LSCimpedance

sdensity

modulationenergy

modulation

• This process can be initiated byeither density or energy modulation



CSR

from: M. Borland et al., FEL-2002



Longitudinal Space Charge• LSC oscillation frequency:

&=f(!mod, Ip, …)

• Compression (factor n) ofmodulated bunch: Ip ' n times,!mod ( n times: & ' n times.

• " Energy modulation getscompressed together with fastergrowth of it’s amplitude

• Initial modulation spectrumseeded by noise is amplifieddepending on what you do withthe beam

0 2 4 6 80

50

100

0 deg 1.42 ps

0 2 4 60

50

100

-5 deg 1.33 ps

0 1 2 3 4 5 60

50

100

-10 deg 1.30 ps

0 1 2 3 4 50

50

100

-13 deg 1.24 ps

0 1 2 3 40

50

100

150

-16 deg 1.10 ps

0 1 2 30

100

200

300

-23 deg 0.63 ps

0 0.5 1 1.5 2 2.50

200

-25 deg 0.43 ps

0 1 2 3 40

200

-21 deg 0.74 ps

0 1 2 3 40

100

200

-19 deg 0.93 ps

Examples of modulated bunch

Compression of modulated bunch

TTFTTFSDLSDL

Z. Huang, W. Graves, C. Limborg, H. Loos,T. Shaftan, Z. WuFrom: W. Graves et al., PAC-2001,H. Loos et al., EPAC-2002,Z. Huang et al., FEL-2003T. Shaftan et al., PAC-2003



LSC oscillation wavelength [m] versus modulation wavelength [um] foruncompressed (50 A) and compressed (220 A) beam

50 MeV60708090100110

100 um

75 um

50 um

37.5 um

25 um

15 um

uncompressed

compressed

* Space charge impedance (Z. Huang):

!"

#$%

&''(

)**+

,-=

./

0

./

0

0

// bb

b

rK

r

r

ZiZ

221

2)( 122

0

* LSC oscillation wavelength:

( )

0

3

0

28

Z

Z

I

Ic

A

SC

!

!

"

#=$

Energy modulation (MeV) versus distance (m)

50 MeV60708090100110

* Example: low-noise RF TWT.



30&70 um initial modulation30&70 um initial modulation

Bunch spectra fordifferent energy

From: T. Shaftan and Z. Huang, PRST-AB-2004

E, MeV

t, ps

E, MeV

t, ps



2 cm2 cm

10 cm10 cm

10 cm10 cm 50 cm50 cm

~120 cm~120 cm

)) ** 5.7 5.7ºº

• Laser-electron interaction in an undulator

induces rapid energy modulation (at 800 nm),

to be used as effective energy spread before

BC1 (3 keV# 40 keV rms)

• Inside a weak chicane for easy laser access,

time-coordinate smearing (emittance growth is

completely negligible)

10 period undulator

800 nm laser pulse800 nm laser pulse

from: Z.Huang, M. Borland, P. Emma, C. Limborg et al., SLAC-PUB-10334, 2004

Laser Heater

No heater

With heater



Modulation in Radiation Sources

Early measurements of modulation after FELK.N. Ricci et al., in Proc. of FEL-2001



Seeded FELs• R.Q.: How to modulate

bunch?

• Seed source creates energymodulation " bunching atfundamental or harmonics

• FEL process takes off froma “known” signal, not fromnoise: longitudinalcoherence

• Concepts: seeding withlasers and HHG sources,self-seeding, seeding withshort pulse, …

Undulatore-

Ce-

Ce-

C

Cascadese-

Seeded FEL

Radiatore-

ModDS

HGHG

Undulatore-

Self-seeding



Conventional lasers/Chirped pulses

• Tunable conventional seedlasers, OPA

• 13th harmonics of Ti:Sa at61 nm, produced in Xe:M.-E. Couprie, in FEL-2005 (1 uJ, 50 fs, 10 Hz)

10600Carbon Dioxide

5000 - 6000Carbon Monoxide

1540Erbium:Glass

2600 - 3000Hydgrogen Fluoride

1064Nd:YAG

720 - 780Alexandrite

690 - 960Ti:Sapphire

630 - 950Laser Diodes

694.3Ruby

337.5 - 799.3 (647.1 - 676.4 mostused)

Krypton

543, 594, 612, and 632.8Helium Neon

532Frequency doubled

Nd:YAG

457 - 528 (514.5 and 488 most used)Argon

511 and 578Copper Vapor

450 - 650Rhodamine 6G

325 - 442Helium Cadmium

353 and 459Xenon Fluoride

308 and 459Xenon Chloride

193Argon Fluoride

WAVELENGTH (Nanometers)LASER TYPE

t

!

e-beam

chirpedlaser pulse

*

http://www.fas.org/man/dod-101/navy/docs/laser/fundamentals.htm$Common Lasers and Their Wavelengths



Compression of modulated bunch• Compression of modulation

wavelength (h1>>h2):

• "Ebeam is determined by RFsystem (f.e., post-compressedchirp can be used)

• "Ebeam is limited by the FELdynamics: how does chirp

affect the FEL output?

E

z

h2

h1+h2

"!modmod

mod

mod

mod

mod

mod

1

2

mod

mod

E

E

E

E

h

h

beam

z

chirp

RF

!

!"#

!

!

!"=#

!

$

%

%

%

%

%

%

%"

"

(, >energy

spreadfixed

T. Shaftan and L.H. Yu, PRE-2005



-15 -10 -5 0 5 10-2

-1.5

-1

-0.5

0

0.5

1

1.5

Chirp, 1/m

Peak wavelength (mag) and

mean wavelength (blue), nm

How does energy chirp affect output radiation?

-15 -10 -5 0 5 100.7

0.8

0.9

1

1.1

1.2

1.3

1.4

Chirp, 1/m

Intensity integral (mag)

and peak (blue), arb. units

0.2 0.4 0.6 0.8 1 1.2

0.4

0.6

0.8

1

1.2

1.4

Spectral width, FWHM (nm)

Intensity integral (mag)

and peak (blue), arb. units

II+BW-1

-15 -10 -5 0 5 100

0.1

0.2

0.3

0.4

0.5

FWHM bandwidth (red) and RMS

peak wavelength jitter (blue, green), nm

Chirp (1/m)

Central wavelength

Peak intensityIntensity integral

Bandwidthand !-jitter

Amplitude$" bandwidth

DUV-FEL experiments, in Proc. of FEL-2005; Also, SASE

from chirped e-beam: G. Andonian et al., in PRL-2005

Energy chirp, m-1



Trends in HGHG spectrum

263.5264

264.5265

265.51

2

3

4

5

6

7

8

9

10

0

50

Tim

e,s

Wavelength, nm

SpectralIntensity, arb. units

Long-term (~10 s) wavelength drift due toaccelerator-laser drifts

262 263 264 265 2660

0.2

0.4

0.6

0.8

1

Wavelength, nm

Spectral intensity, arb. units

HGHG

0.23 nm FWHM

SASE x105

Wavelength (nm)

Inte

nsit

y (a

.u.)

HGHG

HGHG and SASE spectra



What may modulation content in electron beam look like?

E

z

z

I

before DSafter DS

bunching content

• Symptoms: broadening of spectrum,reduction of peak intensity; loss oflongitudinal coherence• Trajectory/beam size are stable "" longitudinal effect• Diagnosis: Detuning due to drive laser –RF phase drift" charge (, compression (, " peak current (, energy (, " FEL gain (

• saturation comes later in theradiator• local chirp varies "can createmodulation of peak current along thebunch

• this will affect FEL output spectrum

262 263 264 265 2660

0.2

0.4

0.6

0.8

1

Wavelength, nm

Spectral intensity, arb. units

coherent

reduction ofcoherency



• Self-seeding schemes: Pellegriniet al., Saldin et al., S. Biedron etal.,

• Quasi-isochronous SR: D.A.G.Deacon (~1980)

• From: A. Matveenko, O.Shevchenko and N.A. Vinokurov,in FEL-2004 " wavelength of 50 nm

• Effect of quantum fluctuations ofSR on microbunched beamtransport is a limiting factor (V.Litvinenko, see also Optics-freeFEL Oscillator in FEL Prize Talk,2005, Å-scale feedback)

• Emittance, energy spread arelimiting factors 65

70

75

80

85

0 20 40 60 80 100 120

ln(|b|

2)

z, m

undulator bend

Degree of bunching

Self-seeded tunable FEL schemes



-1.5 -1 -0.5 0 0.5 1 1.5

x 10-11

0

0.5

1

1.5

2

2.5

3

3.5

4

UV Laser

Input

Time

Diagnostics

RF Gun :

5 MeV

RF Accelerating

Sections:

75 MeV

Terahertz

Diagnostics

The Source Development Laboratory at

Brookhaven National Laboratory

This work was carried out with the support of the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences,

under Contract No. DE-AC02-98CH10886, in addition to the Joint Technology Office, Army Research Laboratory and Office of Naval Research.

100 200 300 400 500 600

50

100

150

200

250

300

350

400

450

E-Beam RF 0-Phase

Measurement

0

1

Terahertz Filters

Electron Beam Premodulation at the Photocathode

Courtesy of J. Neumann

Limitations on tunability range: drive laser bandwidth and LSC



Conclusions

• Modulated beams in high-energy machines are rich and diversephenomena• There are harmful collective effects and effective cures for them

! Landau damping, laser-heater! Elimination of noise sources that seed the effects! Irreproducibility and unpredictable time patterns of theirappearance! Need for fast and reliable diagnostics on micro-scale

•Useful modulation in radiation sources! Seeding and chirping of high-brightness bunch! Tuning modulation wavelength! Premodulation at photocathode for THz production! Tunable self-seeded schemes

T. Watanabe, Superradiance in a single-pass seeded FEL, Thursday, WG-3



Å-scale Feed-back• Use lower energy low current e-beam with VERY

LOW emittance and low energy spread for thefeed-back

• The feed-back-beam is energy-modulated andcarries-on the modulation to the entrance of theFEL

High Gain FEL

Fresh e-beam Used e-beam Photons

Radiator Modulator

e-beam Source

Photons

Courtesy of V. Litvinenko, BNL



0

1 103

2 103

3 103

4 103

-200 -100 0 100 200

Intens

ity

fs

start

0

50

100

150

200

-200 -100 0 100 200

Intens

ity

fs

DS1

0

50

100

150

200

-200 -100 0 100 200

Intens

ity

fs

BQ2

0

50

100

150

200

-200 -100 0 100 200

Intens

ity

fs

BQ50

50

100

150

200

-200 -100 0 100 200

Intens

ity

fs

DS2

0

1 103

2 103

3 103

4 103

-200 -100 0 100 200

Intens

ity

fs

End

Tracking Result of Hamilton Equation in Curvilinear System

Courtesy of H. Hama, Tohoku University

Isochronous THz ring: preservingbunch form

Documents

High-brightness electron beams with tunable … electron beams with tunable modulation Timur Shaftan ... Helium Neon 543, 594, 612, ... Terahertz Diagnostics The