Funded by theEuropean Union

The XLS-CompactLight Design Study
Federico Nguyen* – August 25th 2021
on behalf of the XLS-CompactLight Collaboration*F. Nguyen
August 25th 2021

Fusion and Technologyfor Nuclear SafetyDepartment

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OutlineüIntroduction: (two) Free-Electron Laser (FEL) applicationsüThe XLS-CompactLight projectüTechnology driver: short period undulators

üUser driver: FEL performanceüConclusions & outlook

F. Nguyen
August 25th 2021

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Light emission in insertion devices

For each device: anelectron beam entering
the magnet insertioneB u= 0.94
deflection
strength u [cm]K='
B[T]2⇡me c<latexit sha1_base64="vogWKsxpFkrbjz27W2ZTWh1lFJY=">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</latexit>

KK

1 ! wiggler : also ✓ &1

1

1 ! wiggler : also ✓ &111
K ' 1 ! undulator : ✓ ⇠ 1p
<K ' 1 ! undulator : ✓ ⇠ p N<uNuHigh quality e-beam:bunching happens!

F. Nguyen
August 25th 2021

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F. Nguyen
August 25th 2021

FEL: undulator & bunching

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FEL: an accelerator to investigate matter

Particle Accelerators areused ascoherent photon sources
with applications inPhysics, Chemistry,
Biology and Medicine

Two target X-ray FEL applications (out of many*):

1. Chemical properties through magnetic polarization
2. Coherent diffraction imaging of biological samples*A. Mak, P. Salén, V. Goryashko and J.A. Clarke, FEL Science Requirements and Facility Design,
https://www.compactlight.eu/uploads/Main/D2.1_XLS_Specification.pdf
F. Nguyen
August 25th 2021

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X-ray magnetic properties of materials
X-ray magnetic circular dichroism (XMCD) isthe difference of X-ray absorption spectra(XAS) taken in a magnetic field:
left circularly polarized light −right circularly polarized light

G. van der Laan & A.I. Figueroa / Coordination
Chemistry Reviews 277 (2014) 95

F. Nguyen
August 25th 2021

• XMCD allows for element and site specificstudies• Great interest in ultrafast (< 1 ps)
magnetic dynamics with switchable FEL
polarization

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Coherent imaging of biological samples
Coherent photons hit
the sample, creating adiffraction pattern
The detector image is theFourier Transform of thesample electron density

3D images are obtained processing
several diffraction patterns

X-ray FEL virus 3D reconstruction

The sample is destroyed by the FEL
photons shot, so many identicalsamples are needed
Ideal technique to get 3D images ofviruses in their native environment
F. Nguyen
August 25th 2021

T. Ekeberg et al.
Phys. Rev. Lett. 114 (2015) 098102

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The CompactLight (XLS) Collaborationv

The XLS Collaboration gathers several International Institutions with the aim at promoting designand construction of the next generation FEL sources with innovative accelerator technologiesv

The objective is the design of a 5.5 GeV beam energy X-band Linac, based on the CLIC technology,
to drive an FEL facility with Soft and Hard X-ray options

26 Institutions+ 5 Ass. Partners
F. Nguyen
August 25th 2021XLS

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The main goal is to facilitate
the widespreaddevelopment of X-ray FEL
facilities across Europe andbeyond, by making themmore affordable to constructand operate through theoptimum combination ofaccelerator technologies
We plan to use of the mostadvanced concepts for:ØHigh brightness electron
photoinjectorsØVery high gradientaccelerating structuresØNovel short period
undulators

The XLS project goal
Horizon2020 – Work Programme 2016-2017
Research & Innovation INFRADEV-1-2017 Design Studies
Duration: from 01.01.2018 through 31.12.2021, Grant amount: 3 M€

XLS

Anticipated XLS
performance comparedwith other existing FELor SR facilities
The main challenge is onthe size reduction of theXLS facility wrt the others

The more compact FEL à the more affordable and easy-to-implement facility à fit any University campus
F. Nguyen
August 25th 2021

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The XLS project structure
WP2 – FEL Science requirements and Facility Design

F. Nguyen
August 25th 2021

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XLS parameter tables
FEL parameter wishlist (from users’
requirements and science cases):ØRepetition rate up to 1 kHzØTwo colors operation

Ø

Simultaneous SXR - HXR operation

In addition: a peak brilliance of about1031 SXR - 1033 HXRphotons/s/mm2/mrad2/0.1%BW
3 discrete beam working points:
Parameter
Beam Energy
Photon Energy Range
Minimum Peak Current *RMS Slice Energy Spread
Normalised EmittanceBunch Charge
F. Nguyen
August 25th 2021

Beam Parameters
UnitGeV
keVkA%
mm-mradpCHard X-rays
5.5
3.9
2.75
16 - 8
8-44-25.0
2.5
1.50.010.014
0.02Soft X-rays
1.95
1.37
0.97
2-1
1 - 0.5 0.5 - 0.25
0.925
0.65
0.35
0.028
0.04
0.056
0.275

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F. Nguyen
August 25th 2021

Linac baseline layout

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FEL main character: magnetic undulatoreB uK=' 0.94 B[T]2⇡me c<latexit sha1_base64="vogWKsxpFkrbjz27W2ZTWh1lFJY=">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</latexit>u [cm]

à resonant wavelength

Magnetic field also a function of λu, and gap<latexit sha1_base64="RiB3YD2LqF1e58RE3i+Ya5cc8oE=">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</latexit>

λu
incoherentemission

B / expbunching"a✓gu◆+b✓coherentemission

gu◆2 #oscillations are confined in a plane(à linearly polarized light) or follow
a helix (à circularly polarized light)

Several undulator configurations have been
scrutinized and compared on the basis oftechnology readiness and FEL performance
Courtesy of J. Chavanne

F. Nguyen
August 25th 2021

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Undulator technology selection criteria

Courtesy of N. Thompson

ü In general, SCUs provide larger magnetic field at the same gap,period à the same short wavelength (or high photon energy)
will be covered with higher K strength and magnet field valuesü This translates into a higher FEL interaction à higher photon
pulse energy & shorter length by which the optimum (saturation)
FEL power is reached at the end of the exponential growth:saturation length Lsat
ü This expectation is confirmed by the FEL full 3D simulation withthe XLS electron beam parameters
F. Nguyen
August 25th 2021

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XLS requests & considerations on undulators
ü Both Hard and Soft X-ray FEL lines should havethe same undulator devices
ü In both cases, a factor 2 wavelength tuning(varying the magnet gap or the SC coil current)
is requested

Eγ = 8 keV

ü The maximum peak brilliance and the shortest
saturation length (would like a bright &compact source) are desired: maximum B/Lsat
ratio

Eγ = 16 keV

Courtesy of D. Dunningü Each line curve is an undulator configurationor technology that is weighted by its B/Lsat
ratio: the most performant ones are hightemperature superconducting devices, butthey are not considered mature enough to be
deployed in a FEL user facility
ü The choice is a NbTi helical superconducting
undulator

F. Nguyen
August 25th 2021

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Helical SCU design

Courtesy ofA. Bernhard

Winding trials ongoing at RAL on a 30 cm model,
13 mm period
Full former wound with copper wire, startingß with SC wire
Courtesy of B. Shepherd
F. Nguyen
August 25th 2021

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Considerations on variable polarization

Important to have variable and selectable polarization, to operate XMCD experiments as an example
Courtesy of H.M. Castaneda Cortes

q Helical SCU with fixed circularpolarization
The choice is: scheme III
ü Less expensive than scheme Iü More efficient than scheme II
F. Nguyen
August 25th 2021

q Permanent magnet afterburner withvariable polarization

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Variable polarization FEL performance

Comparison of FEL pulse
energy growth among
SCU only, AB only & XLS(SCU+AB) configurations,targeting Eγ = 250 eV

Courtesy of H.M. Castaneda Cortes

ü XLS (SCU+AB) has a growth shorter (~ 40%) than AB only and slightly longer (~ 13%)than SCU only, that has no variable polarization
ü At the price of delivering about 2.5 times lower pulse energy, but still in the ballparkof ~ 200 µJ, and having polarization switch control as a unique bonus

F. Nguyen
August 25th 2021

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Start-2-end HXR performanceü Wish to prove that the upper FEL photon energy limit 16 keV is feasible with the full chain of thebeam transport from the cathode through the last undulator exit
ü Most of the beam quality deteriorating sources due to collective effects – i.e. coherent synchrotron
radiation (CSR), bunch space charge and wakefields – are accounted for in the full transfer line

At undulator entrance, the beam
exhibits a transverse deformation
along bunch length due to CSR àcausing FEL gain degradation along theundulator line
Still the peak brilliance stays in theballpark of about 5 x 1032
photons/s/mm2/mrad2/0.1%BW

Courtesy of H.M. Castaneda Cortes
F. Nguyen
August 25th 2021

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Funded by theEuropean UnionConclusions

ü

XLS will offer challenging FEL schemes with a broad range of operating modes, by meansof affordable and compact X-band technology (see also CLIC studies), e.g. simultaneous
operation of HXR and SXR at 100 Hz, and SXR up to 1 kHzü

A thorough and comprehensive FEL analysis selected NbTi superconducting undulators
as the magnets technology (addressed alternatives: cryogenic PM, low temperature NbSn, hightemperature structures)üFEL 3D simulation with selectable polarizationin the SXR proven to meet the requirements

ü

Full start-2-end simulation embedded witheffects degrading the beam quality provedthat the peak brilliance requested for probing
biological samples is within reach
Please, stay FEL-tuned!
F. Nguyen
August 25th 2021

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XLS technology implementation: EuPRAXIA² NbTi SCU will be an option² INFN-Fermilab-ENEA
collaboration² Planar prototype underconstruction

EuPRAXIA@SPARC_LAB layout @ Frascati

F. Nguyen
August 25th 2021

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Thank you!
CompactLight@elettra.eu

www.CompactLight.eu

CompactLight is funded by the European Union’s Horizon2020 research and innovation programme under Grant Agreement No. 777431.

Funded by theEuropean Union

XLS upgraded layout

UPGRADE 1
SchematicGHz
SPLITTER

0.3 GeV
LINAC0LINAC1

LINAC2

LINAC3VAR POL.

FEL-1

AB1

FIXED POL.

VAR POL.

FEL-2

AB2

SXR
BEAM
DUMP

TIMINGCHICANESPLIT

PI LASER
Split
PI
Laser

FIXED POL.

C-bandX-bandSTATIONSHXRSTATIONS

0.97 to 1.95 GeV @ 1000 Hz (SXR/SXR)
2.75 to 5.5 GeV @ 100 Hz (HXR/HXR)

100 Hz KICKER

0.97 to 1.95 GeV @ 1000 Hz (SXR/SXR)
2.75 to 5.5 GeV @ 100 Hz (HXR/HXR)+
2.75 to 5.5 GeV @ 100Hz (SXR/HXR at the same time)
2 klystrons x LINAC Module:• CPI VKX-8311 @ 50 MW• CPI (Canon E37113*) @ 10 MW
F. Nguyen
August 25th 2021

<Eacc> = 65 MV/m @ 100 Hz<Eacc> = 30.4 MV/m @ 1 kHz

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The XLS work packages

Technology options surveyed and down-selectedon the basis of Physics performance & feasibility,risks and costs: in a way very similar to HighEnergy Physics experiments when deciding theirsensors or detectors technology

XLS Conceptual Design
Report to be released byDecember 31st 2021
F. Nguyen
August 25th 2021

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