Compact radiation sources based on laser-
plasma wakefield accelerators
Silvia Cipiccia on behalf of Prof. Dino JaroszynskiUniversity of Strathclyde
Outline of talk
• Large and small accelerators + high power lasers• Laser driven wakes• Ultra-short bunch electron production using wakefield
accelerators • Initial FEL experiments• Betatron gamma ray source• Conclusion
CERN – LHCCERN – LHC27 km 27 km circumferencecircumference
• SLACSLAC
50 GeV in 3.3 km
20 MV/m
7 TeV in 27 km
7 MV/m
Large accelerators depend on superconducting Radio Frequency cavities and superconducting magnets
Synchrotrons light sources and free-electron lasers: tools for scientists
Synchrotron – huge size and cost is determined by accelerator technology
Diamond
undulatorsynchrotron
DESY undulator
The future of electron accelerators
27 Km circumference
2 miles long
Electrons energy:
50MeV - 1GeV
4 cm
High energy electron beams in few mm
…..
an industrial
revolution?
Plasma Replaces RF Cavities
Small Scale Source = Big Applications
Particles accelerated by electrostatic fields of plasma waves
Accelerators:
Surf a 10’s cm long microwave – conventional technology
Surf a 10’s mm long plasma wave – laser-plasma technology
2
max
2
3ga
[V/cm]E e n
Wakefield acceleration
p
Dephasing length: which gives a maximum energy:
0g
p
204 3 ,d g pL c a 2
0
2
3 ga
Modelling of Laser Wakefield Acceleration
laser pulse envelopeelectrostatic wakefieldbunch densityenergy density of wakefield
z-vg t (units of λp)Movie shows • laser pulse deforms as it transfers energy to the plasma and sets up wakefield • wakefield changes as a result of laser pulse deformation • electron bunch modifies wakefield as it takes energy from the plasma • electron bunch slips from a region of E>0 to E<0 and reaches max. energy
OSIRIS – PIC code developed by W. Mori and L. Silva OSIRIS – PIC code developed by W. Mori and L. Silva
Bubble Regime
Electron acceleration
• energy gain limited by dephasing, caused by difference between velocities of electron and wakefield
• scaling favours low plasma density
gwfel vvcv
12/32/1 pppdeph nnnLE
log(γ)
(fs) /c
electron orbit
pulse intensity
separatrix
note logarithmicenergy scale
Energy spread
accelerating wakefield
wakeenergy density
bunch density
at injection
(fs) /c
at dephasing
• energy spread induced by spatial variation of accelerating field along bunch• can be compensated for by combined effect of dephasing and beam loading • requires precise tuning of injection phase, bunch charge and bunch length
• during first half of acceleration, front of bunch gains more energy than rear → energy spread increases• during second half of acceleration, rear of bunch gains more energy than front → energy spread decreases and reaches minimum
210
BENDINGMAGNET
UNDULATOR
ELECTRON ENERGYSPECTROMETER
LASER IN
PLASMA ACCELERATOR
RADIATIONSPECTROMETER
8 m
TOPS laser: 1 J @ 10 Hz; = 800 nm; 30 fs
Jaroszynski et al., (Royal Society Transactions, 2006)
ALPHA-X Advanced Laser Plasma High-energy Accelerators towards X-rays
Experimental Results: energy stability
Electron Spectrometer: 200 consecutive shots (spectrum on 196 shots)
69 90 124 185Energy (MeV)
100 consecutive shotsMean E0 = (137 4) MeV
2.8% stability
Highest energy achievable at Strathclyde: 360 MeV in 2 mm
Narrow energy spread beams
100 110 120 130 140 150
8000
10000
12000
14000
16000
18000
Cha
rge/
unit
ener
gy [a
.u.]
Energy [MeV]
0.75%
63 MeV 170 MeV
Absolute energy spread < 600 keV
Strathclyde
Experimental Results – emittance
• divergence 1 – 2 mrad for this run with 125 MeV electrons• average N = (2.2 0.7) mm mrad• best N = (1.0 0.1) mm mrad• Elliptical beam: N, X > N, Y • Upper limit because of resolution
• Second generation mask with hole ~ 25 m and improved detection system
Experimental results: beam pointing
• 500 consecutive shots at Strathclyde• narrow divergence (~2 mrad) beam• wide divergence low energy halo• X = (7 3) mrad, Y = (3 2) mrad
• 8 mrad acceptance angle for EMQs• 25% pointing reduction with PMQs installed
-10
0
10
20
-10 0 10 20
Y[m
rad]
X [mrad]
no PMQs PMQs in
5 mrad
2 fs bunch measured at 1 m from source
Peak current several kiloAmperes
0 2 4 6 8 10 12 14 16 18
0.000000
0.000005
0.000010
0.000015
0.000020
0.000025
0.000030
0.000035
Measured TR signal 1 fs 1.5 fs 2 fs 2.5 fs 3 fs 4 fs
TR
(J/
m)
Wavelength (m)
Strathclydeexperiments in spring 2010
Experimental results:Bunch length measurements Coherent Transition Radiation
ALPHA-X Advanced Laser Plasma High-energy Accelerators towards X-rays
Compact R&D facilities to develop and apply femtosecond duration particle, synchrotron, free-electron laser and gamma ray sources
70 75 80 85 90 95 1000
250
500
750
1000
No
. ele
ctr
on
s/ M
eV
[a
.u.]
Electron energy [MeV]
(b)
(a)
electron beam spectrum
beam emittance: <1 mm mrad
CTR: electron bunch duration:
1-3 fs
0.7%
FEL
1J 30 fs
1019 cm-3
0 5 10 15
0.0
0.1
0.2
0.3
Measured TR signal 1 fs 1.5 fs 2 fs 2.5 fs 3 fs 4 fs
TR
(J/
m)
Wavelength (m)
= 2.8 nm – 1 m (<1GeV beam)
Extending to higher energy:Strathclyde plasma media
• Extend energy range to multi GeV
• Study plasma media – extend length relativistic self focussing, gas cells and channels
• Stable electron beam generation
4 cm
Gas Cell10 J, 50 fs
E0 = 690 MeV, / MEAS ~ 4%
E0 = 770 MeV, / MEAS ~ 4%
E0 = 610 MeV, / MEAS ~ 4.5%
RAL GEMINI: Measurements limited by spectrometer resolution – maximum energy measured 850 MeV
First undulator radiation demonstration with LWFA
• Strathclyde, Jena, Stellenbosch collaboration
• 55 – 70 MeV electrons
• VIS/IR synchrotron radiation
Schlenvoigt .., Jaroszynski et al., Nature Phys. 4, 130 (2008)
Gallacher, ….Jaroszynski et al. Physics of Plasmas, Sept. (2009)
• Measured / ~ 2.2 – 6.2%
• Analysis of undulator spectrum and
modelling of spectrometer
/ closer to 1%
Recent VUV radiation measurements at Strathclyde
Recent VUV radiation measurements at Strathclyde
Q = 3.1 pC;σγ/γ = 3.5% (limit of the spectrometer)
Recent VUV radiation measurements at Strathclyde
Radiation sources: Synchrotron and Free-Electron Laser (FEL): a potential 5th generation light
source• Use output of wakefield accelerator to drive compact synchrotron light source or FEL
• Take advantage of electron beam properties
• Coherent spontaneous emission: prebunched FEL I~I0(N+N(N-1)f(k))
• Ultra-short duration electron bunches: I >10 kA
• Operate in superradiant regime: FEL X-ray amplifier (self-similar evolution)
Potential compact future synchrotron source and x-ray FEL
Need a low emittance GeV beam with < 10 fs electron beam with I > 10 kA
Operate in superradiant regime: SASE alone is not adequate: noise amplifier
Need to consider injection (from HHG source) or pre-bunching
SCALING LAWS
• Betatron frequency: • Transverse momentum:• Divergence: • Critical photon energy:• Efficiency:
• Wavelength:
/ 2p
ea n r
/a 2
c eE n r
Betatron radiation emission during LWFA
/phot cycleN a
2 22 2
2 3/2
31 ( ) 1 ( )
2 2 2h e ee p e
a ac
h h
Synchrotron, betatron and FEL radiation peak brilliance
ALPHA-X ideal 1GeV bunch
FEL: Brilliance 5 – 7 orders of magnitude larger
ucm
n = 1 mm mrad
e = 1-10 fs
Q = 1 – 20 pC
I = 1-25 kA
< 1%
I(k) ~ I0(k)(N+N(N-1)f(k)) FEL = spontaneous emission x 107
betatron source
The Scottish Centre for the Application of Plasma Based Accelerators: SCAPA
1000 m2 laboratory space: 200-300 TW laser and 10 “beam lines” producing particles and coherent and incoherent radiation sources for applications: nuclear physics, health sciences, plasma physics etc.
Strathclyde Technology and Innovation Centre
Conclusions• Laser driven plasma waves are a useful way of accelerating charged particles
and producing a compact radiation source: 100 – 1000 times smaller than conventional sources
• Some very good properties: sub 10 fs electron bunches potentially shorter (< 1 fs?) and high peak current (up to 35 kA?), n < 1 mm mrad, < 1%?.
• Slice values important for FEL - potentially 10 times better. Wide energy range, wide wavelength range: THz – x-ray
• Good candidate for FEL – coherence & tuneability• Betatron radiation – towards fs duration gamma rays• Still in R&D stage – need a few years to show potential• Challenges: rep rate, stability, energy spread and emittance, higher charge
and shorter bunch length, beam transport• Synchronised with laser – can combine radiation, particles (electrons, protons,
ions), intrinsic synchronisation• A compact light source for every university or 5th Generation light source? A
paradigm shift?• Setting up a new centre of excellence: SCAPA: the Scottish Centre for the
Application of Plasma based Accelerators: based in Glasgow and part of a pooling effort: SUPA – The Scottish Universities Physics Alliance
Strathclyde (students and staff):
Team: Dino Jaroszynski, Salima Abu-Azoum, Maria-Pia Anania, Constantin
Aniculaesei, Rodolfo Bonifacio, Enrico Brunetti, Sijia Chen, Silvia Cipiccia, David
Clark, Bernhard Ersfeld, John Farmer, David Grant, Ranaul Islam, Riju Issac,
Yevgen Kravets, Tom McCanny, Grace Manahan, Adam Noble, Guarav Raj,
Richard Shanks, Anna Subiel, Xue Yang, Gregory Vieux, Gregor Welsh and Mark
Wiggins
Collaborators: Gordon Rob, Brian McNeil, Ken Ledingham and Paul McKenna
ALPHA-X: Current and past collaborators:
Lancaster U., Cockcroft Institute / STFC - ASTeC, STFC – RAL CLF, U. St. Andrews, U. Dundee, U. Abertay-Dundee, U. Glasgow, Imperial College, IST Lisbon, U. Paris-Sud - LPGP, Pulsar Physics, UTA, CAS Beijing, LBNL, FSU Jena, U. Stellenbosch, U. Oxford, LAL, PSI, U. Twente, TUE, U. Bochum, ....
ALPHA-X project
Current Support:
EPSRC, E.U. Laserlab, STFC, University of Strathclyde
consortium
Thank you