COXINEL: a test facility for demonstrating FEL

amplification with Laser wakefield acceleration

Martin Khojoyan on behalf of COXINEL team

Designing future X-ray FELs

August 31-September 2, 2016

� Introduction

� COXINEL setup and corresponding simulation tools

� First experimental observations

� Summary and outlook

� Introduction

� COXINEL setup and corresponding simulation tools

� First experimental observations

� Summary and outlook

Laser wakefield acceleration (LWFA)

T. Tajima and J. M. Dawson, Phys.

Rev. Lett. 43, 267 (1979) 267.

Courtesy V. Malka

W. P. Leemans et al. , Nature Physics 418, 2006, 696.

Intense laser focused in a gas jet Perturbation of the electronic density

S. P. D. Mangles et al., Nature 431, 535-538 (2004) , C. G. R. Geddes et al.,

Nature 431, 538–541 (2004) , J. Faure et al., Nature 431, 541-544 (2004).

V. Malka et al, Phys. Plasmas 12, 056702 (2005) ;

J. Faure et al., Nature 444, 737-739 (2006);

E. Esarey et al., Rev. Mod. Phys., 81 (2009)

Large accelerating gradients: GV/m

� Energy: 0.1 - 1 GeV

� Charge: 1 - 100 pC

� Energy spread (depending on charge): 1-10 % (an order of magnitude larger for FEL)

� Normalized emittance: 0.1-1 mm mrad

� Divergence: 1 mrad level

� Bunch duration: 1-10 fs (shorter than slippage length)

LWFA electron beam properties:

LPA beam properties today

Large divergence and energy spread to be improved at the source

or handled during the beam transfer !

LPA based undulator radiation

F. Gruener et al., arXiv:physics/0612125v1, 2006

K. Nakajima, Nature Physics, 4 (2008) 92

H. P. Schlenvoigt et al., Nature Physics, 4, 130-133, 2008

M. Fuchs et al., Nature Physics 5, 826 (2009)

M. P. Anania et al., Appl. Phys. Lett. 104, 264102 (2014).

Undulator radiation (spontaneous emission)

Amplified undulator radiation (FEL)?

LPA � few fs, 1 π mm.rad, few % energy spread

LWFA beams are orthogonal to the conventional beams !

LWFA beams vs. conventional beams

The LFWA beams have a micrometer beta function

The beam has to be refocused by a strong and short

magnets located as close as possible to the source

M. Migliorati et al., PTST-AB 16, 011302 (2013).

P. Antici et al., J. Appl. Phys. 112, 044902 (2012).

K. Flöttmann, PRST-AB 6, 034202 (2003).

LPA beams after plasma

at source after drift after quadrupole

Electron beam distribution in transverse phase space at different positions along the COXINEL line.

2 2 2 2

0,

total chromγε γ ε γ ε= +

T. Mehrling et al., PRST-AB 15, 111303 (2012).

2~

xσ ′Bunch lengthening due to trailing particles

δ<0

δ>0

The effects amplified with a distance !

2~ xEchrom ′σγσγε

A.G. Khachatryan et al., PRST-AB 10, 121301 (2007).

Handling LPA beams: energy spread

before chicane after chicane

δ<0

δ>0

δ56

~ rs∆

Bunch decompression

A. Maier et al., PR X 2, 031019 (2012).

Transverse gradient undulator (TGU)T. Smith et al., J. Appl. Phys. 50, 4580 (1979).

Z. Huang et al., PRL 109, 204801 (2012).

Courtesy P. Baxevanis

Variation of undulator field with transverse position

Correlation with horizontally dispersed electron beam

No decompression � high peak current

Difficult to transport and match the beam to the undulator …

Reduced slice energy spread, longer bunch

duration: easy FEL

Handling LPA beams: divergence

Plasma lens: experimentally realized at LOA

C. Thaury et al., Nat. Comm. 6, 6860 (2014).

R. Lehe et al., PRST AB 17, 121301 (2014). L – distance between two jets

2.5 times reduction of divergence !

Adiabatic matching

Tapering plasma density profile at vacuum-plasma and plasma-

vacuum interfaces

Smaller divergence and constant emittance after plasma

K. Flöttmann, PRST AB 17, 054402 (2014).

X. L. Xu et al., PRL 116, 124801 (2016).

� Introduction

� COXINEL setup and corresponding simulation tools

� First experimental observations

� Summary and outlook

Motivation

COXINEL1:COherent X-ray source INferred from Electrons accelerated by Laser

� COXINEL project aims at demonstrating a Free Electron Laser (FEL) amplification from a Laser Wakefield Acceleration2 (LWFA)

� Electrons are generated by 2x 60 TW laser in the Laboratoire d’optique appliquée (LOA)

� Beam transfer line was prepared at SOLEIL and installed at LOA

1. M.E. Couprie at al., Proc. of FEL 2014.

2. T. Tajima and J.M. Dawson, PRL, vol. 43, No. 4 (1979).

Chromatic matching (CM) *

116 126 011 12

21 22 216 226 0

r r xr rx

x r r r r xδ

= + ′ ′

Linear Chromatic

TRANSPORT code notation 2nd order **

Source to Image (S2I) optics

2260r =

2

22 126chrom xr r δγε γ σ σ′=

** K. Brown., SLAC Report No. 75 (1982).

waist at und. center

*A. Loulergue et al., New J. Phys. 17, 023028 (2015).

120r =

011min_ xx r σσ =

Chromatic matching

� Slice e-beam waist and FEL wave synchronization by adjusting the chicane strength

� Up to two orders of magnitude improvement in FEL peak power over 5 m undulator !

without CM

with CM

waist – energy correlation

energy – position correlation

+

waist – position correlation !

Adding chicane �

=

Beam waist slipping from tail to head like FEL wave does !

und

photonrrr

λ

λ

31261156

−=

Synchronization conditionAfter first triplet �

Set of 4 EM quads �

Chromatic matching

LPA beam parameters for COXINEL studies (200 nm)

LWFA beam parameter Value

Energy, MeV 180

Charge, pC 34

Peak current, kA 4

Bunch rms length, µm 1

Relative rms energy spread, % 1

Transverse rms divergence, mrad 1

Normalized emittance, π mm mrad 1

6D Gaussian beam distribution without any correlations.

Tools for electron beam transport

Home-made code

� Beam matching inside the undulator using BETA1 code

� Tracking based on symplectic mapping through each magnetic element (assuming hard edge field profile)

� Includes collective effects such as space charge (SC), coherent synchrotron radiation (CSR2) and Wakefields

� Estimated calculation time including space charge (1Mp): ~ 10 minutes

Astra3 (A Space charge TRacking Algorithm)

� Tracking based on 4th order Runge-Kutta integration to solve the equation of motion through the magnetic fields

� Well established algorithm for the space charge field calculation

� Estimated calculation time including space charge (1Mp): ~ 3 hours

Goal� Study the dynamics of LPA beams by comparing two different tracking softwares

� Study the influence of collective effects on the beam performance

1. J. Payet, Beta Code, CEA, SACLAY.

2. E. Saldin et al., NIM A 398, 1997.

3. K. Flöttmann, ASTRA, http://www.desy.de/mpyflo

Beam properties without space charge and without chicane

Normalized rms emittance from two codes Beam envelope and bunch length from two codes

Evolution of beam properties along the COXINEL line from the electron source up to the undulator center.

εx

εz

Home made

Astra

εx

εy

Regular curve: Home made

Dashed curve: Astra σx

σz

Regular curve: Home made

Dashed curve: Astra

Astra

Slice beam output with chicane

Slice beam properties at undulator center. 3D SC calculation algorithm is applied.

Chicane strength fixed to 1.1 mm.

� Increased emittance (~ 10 %)

in the central part with SC

� Additional bunch lengthening

due to space charge

without space charge with space charge

Home made

Astra

Home made

Astra

Home made

Astra

Home made

Astra

Home made

Astra

Home made

Astra

� Consistent results from two

codes

180 MeV, 1 mm mrad, 4 kA, 1 mrad, 1 %

Influence of collective effects on beam performance*

Beam properties at undulator center for baseline COXINEL parameters.

� ~ 5 % increase of slice emittance (central

part) including SC and CSR

� ~ 10 % slice emittance increase (central

part) due to space charge effects

� ~ 25 % slice emittance increase (central

part) including space charge and CSR

+ 3D space charge + 1D CSR No wakes

180 MeV, 1 mm mrad, 4 kA, 1 mrad, 1 %

*M. Khojoyan et al., NIM A 829 (2016) 260-264.

Chicane strength fixed to 1.1 mm

� Introduction

� COXINEL setup and simulation tools

� First experimental observations

� Summary and outlook

COXINEL beamline at LOA

� Beam based alignment with the first QUAPEVA (afterwards the next 2 are set and adjusted one by one)

� Observe the beam in the straight section before EM quadrupoles

� Observe the beam at screen.2 (dispersive section) by adjusting the chicane (energy and energy spread)

� Tune 4 electromagnetic quadrupoles for the beam profiles on screen 4 and screen 5

� Detect the beam charge on ICT1 (inside the chamber) and ICT2 (end of the line)

Strategy of beam transport

Transverse beam profile along the line at one of the best transport settings.

Image analysis: raw image

I_Q1=-0.8A, I_Q2=0.9A,

I_Q3=-0.8A, I_Q4=0.9A.

Beam image on screen 5

Fwhm=57 pixels

Rms=242 pixels

Fwhm=56 pixels

Rms=100 pixels

Scaling factor = 0.031mm / pixel

Image analysis: filtered inside ROI

Fwhm=45 pixels

Rms=85 pixels

Fwhm=39 pixels

Rms=29 pixels

Wiener filtered Image

inside the ROI

Smoothing based on Wiener method

by estimation of local mean

and variance around each pixel

Scaling factor = 0.031mm / pixel

Beam energy

Masked imageFinal image to analyze RAW image

LFWA electrons with large energy spectrum !

dipL B L c

Ex

⋅ ⋅ ⋅=

B - dipole magnetic field

c - the speed of light

x – position on screen

Electron beam on screen 5 and charge at ICT2

E-beam shot-to-shot instabilities Up to 35 pC charge seen by ICT.2 !

Charge at ICT2 over 20 minutes.

1.2 A absolute current in 4 EM quadrupoles.

Data analysis are challenging. Each image should be handled separately. !

Beam studies at screen 5

Transverse fwhm beams size (measured vs. simulated) as function of current in EM quadrupoles.

%10=Eσ

X

Z

Emittance is not preserved in quadrupoles

Beam energy � [50 -250] MeV

� Introduction

� COXINEL setup and corresponding simulation tools

� First experimental observations

� Summary and outlook

Summary

COXINEL aims at demonstrating an FEL amplification from LPA beams as they are produced today !

� LPA beam transport from source to undulator:

� Overall reproducible beam output results from two different tracking codes

� Chicane decompression reduces the space charge influence on the beam performance

� About 25 % slice emittance growth for the COXINEL beam parameters due to SC and CSR

� First beam measurements at COXINEL !

� Electron beam was successfully transported to the end of the beamline

� Relatively high charge electron beam with wide energy spectrum

� Large beam position instabilities with a self injection scheme

� Difficult to threat the data:

unstable beam position and profile + low intensity (low charge) � much more statistics needed

� Start-to-end simulations assuming realistic beam input from LPA

Acknowledgments

Special thanks to the COXINEL team !

Thanks to:

The group of magnetic insertion (GMI)

Thank you for your attention !

European Research Council Advanced Grant COXINEL No. 340015 by M.E. Couprie and X-five Grant

by V. Malka