Compact radiation
sources based on laserplasma wakefield
accelerators
Silvia Cipiccia on behalf of Prof. Dino Jaroszynski
University 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
Large accelerators depend on
superconducting Radio Frequency
cavities and superconducting
magnets
•
7 TeV in 27 km
7 MV/m
SLAC
50 GeV in 3.3
km
20 MV/m
CERN – LHC
27 km
circumference
Synchrotrons light sources and
free-electron lasers: tools for
scientists
Synchrotron – huge size and cost is
determined by accelerator technology
Diamond
DESY undulator
undulator
synchrotron
The future of electron
accelerators
Plasma
High energy
electron
beams in
few mm
Replaces
Cavities
ElectronsRF
energy:
27 Km
50MeV
- 1GeV
circumference
Small
Scale
Source
=
Big
Applications
…..
an industrial
2 miles long
revolution?
4 cm
Particles accelerated by
electrostatic fields of plasma waves
Accelerators:
Surf a 10’s cm long
microwave –
conventional
technology
E [V /cm ]  e n
 m ax 
2 a
2
g
3
Surf a 10’s mm long
plasma wave –
laser-plasma
technology
Wakefield acceleration
lp
Dephasing length: L d  4 c g
2
a 0 3 p ,
g 
 
which gives a maximum energy:
2
3
0
p
 g a0
2
Modelling of Laser Wakefield
Acceleration
laser pulse
envelope
electrostatic
wakefield
bunch density
energy 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
Bubble Regime
OSIRIS – PIC code developed by W. Mori and L. Silva
OSIRIS – PIC code developed by W. Mori and L. Silva
Electron acceleration
•
energy gain limited by dephasing, caused by difference
between velocities of electron and wakefield v el  c  v wf  v g
3 / 2
   E  L deph  n p n p
1/ 2
log(γ)
• scaling
1
 np
favours low plasma density
separatrix
note logarithmic
energy scale
electron
orbit
pulse
intensity
 /c (fs)
Energy spread
• 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
at injection
at dephasing
wake
energy
density
bunch
density
accelerating
wakefield
 /c (fs)
• 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
ALPHA-X
Advanced Laser Plasma Highenergy Accelerators towards X-rays
TOPS laser: 1 J @ 10 Hz; l = 800 nm; 30 fs
LASER IN
PLASMA
ACCELERATOR
ELECTRON ENERGY
SPECTROMETER
UNDULATOR
BENDING
MAGNET
210
8m
Jaroszynski et al., (Royal Society Transactions, 2006)
RADIATION
SPECTROMETER
25
20
Counts
Experimental Results:
energy stability
30
15
10
5
0
130
135
140
145
150
Energy [MeV]
100 consecutive shots
Mean E0 = (137  4) MeV
2.8% stability
Electron Spectrometer: 200 consecutive shots (spectrum on 196 shots)
69
90
Energy (MeV)
124
Highest energy achievable at Strathclyde: 360 MeV in 2 mm
185
Narrow energy spread beams
63 MeV
Charge/unit energy [a.u.]
18000
16000
170 MeV


 0.75%
Absolute energy
spread < 600 keV
14000
12000
10000
8000
100
110
120
130
Energy [MeV]
140
150
Strathclyde
Experimental Results – emittance
• Second generation mask with hole  ~ 25 m and improved detection system
4
3
2
10
-0.75
-0.50
-0.25
0
0.00
-1
Count
1
0.25
0.50
10
(a)
Count
x' [mrad]
• 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
5
(b)
5
0.75
x[mm]
0
0
-2
1
2
3
nx [ mm mrad]
-3
0
5000
10000
arb. counts
15000
0
0
1
2
3
ny [ mm mrad]
 Y [mrad]
Experimental results:
beam pointing
20
10
5 mrad
•
•
•
•
500 consecutive shots at Strathclyde
narrow divergence (~2 mrad) beam
wide divergence low energy halo
X = (7  3) mrad, Y = (3  2) mrad
0
-10
0
-10
10
20
 X [mrad]
• 8 mrad acceptance angle for EMQs
• 25% pointing reduction with
PMQs installed
no PMQs
PMQs in
Experimental results:
Bunch length measurements
Coherent Transition Radiation
0.000035
Measured TR signal
1 fs
1.5 fs
2 fs
2.5 fs
3 fs
4 fs
0.000030
0.000025
TR (J/m)
0.000020
0.000015
2 fs bunch
measured at 1
m from source
Peak current
several
kiloAmperes
0.000010
0.000005
0.000000
0
2
4
6
8
10
12
Wavelength (m)
14
16
18
Strathclyde
experiments in spring
2010
ALPHA-X
Advanced Laser Plasma Highenergy Accelerators towards X-rays
Compact R&D facilities to develop and apply
femtosecond duration particle, synchrotron,
free-electron laser and gamma ray sources
CTR: electron
bunch duration:
1-3 fs
TR (J/m)
0.3
0.2
0.1
0.0
0
5
10
15
Wavelength (m)
electron beam spectrum
1000
No. electrons
/ MeV [a.u.]
Measured TR signal
1 fs
1.5 fs
2 fs
2.5 fs
3 fs
4 fs
750
(b)

500


 0.7%
250
0
70
75
80
85
90
95
100
Electron energy [MeV]
1019 cm-3
(a)
1J 30 fs
beam emittance: <1  mm mrad
l = 2.8 nm – 1 m
(<1GeV beam)
FEL
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
E0 = 610 MeV, / MEAS ~ 4.5%
E0 = 690 MeV, / MEAS ~ 4%
Gas Cell
10 J, 50 fs
E0 = 770 MeV, / MEAS ~ 4%
RAL GEMINI:
Measurements limited by spectrometer
4 cm
resolution – maximum energy measured 850 MeV
First undulator radiation
demonstration with LWFA
• Strathclyde, Jena,
Stellenbosch
collaboration
• 55 – 70 MeV electrons
• VIS/IR synchrotron
radiation
• Measured  / ~ 2.2 – 6.2%
• Analysis of undulator spectrum and
modelling of spectrometer
 / closer to 1%
Schlenvoigt .., Jaroszynski et al., Nature Phys. 4, 130 (2008)
Gallacher, ….Jaroszynski et al. Physics of Plasmas, Sept. (2009)
Recent VUV radiation
measurements at Strathclyde
Recent VUV radiation
measurements at Strathclyde
Recent VUV radiation
measurements at Strathclyde
Q = 3.1 pC;
σγ/γ = 3.5% (limit of the
spectrometer)
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
Betatron radiation emission
during LWFA
SCALING LAWS
•
•
•
•
•
Betatron frequency:     p / 2
Transverse momentum: a    n e r
  a /
Divergence:
Critical photon energy: E c   2 n e r
N
  a
Efficiency:
• Wavelength:

phot / cycle
lh 
l
h 2 e
2
2


a
3 c
2
1


(


)



e
3/ 2
2
h


p e


2


a
2
 (  e ) 
1 
2


Synchrotron,
betatron and FEL
radiation peak
brilliance
I(k) ~ I0(k)(N+N(N-1)f(k))
lu
 1.5 cm
n
FEL = spontaneous
emission x 107
= 1  mm mrad
te
= 1-10 fs
Q
= 1 – 20 pC
I
= 1-25 kA
d/
betatron source
< 1%
FEL: Brilliance 5 – 7
orders of magnitude larger
ALPHA-X ideal 1GeV bunch
The Scottish Centre for the Application
of Plasma Based Accelerators: SCAPA
Strathclyde Technology and Innovation Centre
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.
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, d/ < 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
ALPHA-X project
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, ....
Current Support:
EPSRC, E.U. Laserlab, STFC, University of Strathclyde
consortium
Thank you