Laser-driven high-energy ion sources:

1
Laser-driven high-energy ion sources state-of-the
-art and perspectives for applications
M.Borghesi,
School of Mathematics and Physics
The Queens University of Belfast
John Adams Institute for Accelerator Science
Lecture Series 22 March 2006
2
Talk outline

• Acceleration mechanism
• Present status of laser-ion accelerators
• Main applications
• (deflectometry, radiography, fast ignition,
  particle therapy)
• Requirements
• Energy increase
• Spectral tailoring and collimation

3
Main contributors
QUB Belfast (UK)L.Romagnani. C.A. Cecchetti,
S.Kar, P.A. Wilson , M.Zepf Central Laser
Facility, RAL (UK) D. Neely, R.J.Clarke,
M.Notley, P.Norreys,M.Tolley LULI, Palaiseau (F)
J.Fuchs, P.Antici, P.Audebert, E.Brambrink Univers
ity of Dusseldorf (D) T.Toncian, O.Willi,
G.Pretzler, A. Pipahl, Lawrence Livermore
National Laboratory (US) A.J.Mackinnon, P.
Patel Università di Pisa (Italy) A.Macchi, F.
Ceccherini, F .Pegoraro, T. Lysseikina Institute
de Physique Theorique (Palaiseau) P.Mora,
T.Grismayer Università di Roma "La Sapienza,
(Italy) A.Schiavi Univ. of Nevada (USA) T.
Cowan, E. DHumieres

4
Laser acceleration of ions (long pulses) was
observed from 1960s
C02 data (?10 µm)
Laser couples energy into electrons
1 MeV
Graph Gitomer or Beg
Faster electrons drag ions
E
-

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EION(KeV/AMU)

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10 KeV
-

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-
-


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-

-
-
-


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Data from 1967 to 1983


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-
Laser


-

-
I?2 (Watts cm-2 µm2)
S.J. Gitomer et al, Phys. Plasmas, 29, 2679
(1986)
A.V. Gurevich et al, Sov. Phys. JETP, 22, 449
(1966)
5
Progress of laser technology allows now
relativistic laser-matter interactions
Chirped Pulse Amplification D. Strickland and G.
Mourou, Opt. Commun. 56, 219 (1985)
Pre-CPA pulse length 100 ps -1 ns, P lt TW
Post CPA pulse length 30 fs - 1 ps, P gt PW
Relativistic interaction regimes (voscc)
Efficient and directional energy coupling into
relativistic electrons
6
Typical parameters of lasers used in these studies
LULI laser Ecole Polytechnique, France E20 J, l
1 µm, t 350 fs, Intensity 3-4 1019 W/cm2
VULCAN laser Rutherford Appleton Laboratory, UK E
100 J, l1 µm, t 1 ps Focal spot 10-15 µm
FWHM Intensity 7-8 1019 W/cm2





High intensity pulse (fs/ps)
VULCAN Petawatt l 1 µm, t 500 fs E
500 J , f.s.10 µm FWHM Intensity 1021 W/cm2
107- 108
Long pulses (ns, gt50 J)
JanUSP laser LLNL, USA E 10 J , l 0.8 µm, t
100 fs Focal spot 5 µm FWHM Intensità 2-3
1020 W/cm2
Two CPA pulses
ASE (Amplified Spontaneous Emission, ns)
7
Proton acceleration mechanism electrostatic
force due to fast electrons
Several processes can be responsible for
laser-induced acceleration of
n
e
electrons to very high energies
n
c
L
a
s
e
r
8
Proton acceleration mechanism electrostatic
force due to fast electrons
Surface contaminant (C,H,O)
Metal foil
Target Normal Sheath Acceleration (TNSA)
9
Plasma expansion driven by a Debye sheath at the
front
Virtual cathode
t0
Initial Electric Field Ez kThot/elD 1012 V
/ m

• high field
• cold surface
• neutralized beam

?
n
nion
ncold

E ?(nhotThot)0.5
nhot
z0 lD
z
?
E decreases with time, electrons transfer energy
to ions
tgt0
In expanding sheath Ez (t) kThot(t) / e
lo(t)
P.Mora, PRL,90, 185002 (2003)
Quasineutral, ambipolar expansion
10
Particle in cell simulations highlight the 3-D
structure of of proton acceleration
A.Pukhov, Dusseldorf University
3DPIC Simulations, VLPL code
B-field
Thermal expansion
E-field
Debye sheath
11
Ion beams are typically polychromatic and
divergent
Energy (MeV)
1
3
5.5
7.5
40 µm target
9
LULI 100TW
10.5
I3 1019 W/cm2
t350 fs
High intensity pulse
12
Why are laser-accelerated ion of interest?

• Extreme laminarity rms emittance lt 0.002 ?
  mm-mrad
• Short duration source 1 ps
• Low divergence 10 (can be collimated/focused)
• High energy - 60 MeV at present
• High brightness 1011 1013 protons/ions in a
  single shot (gt 3 MeV)
• High current (if stripped of electrons) kA range

13
Laser-accelerated ions maximum energy
M.Borghesi et al, Fusion Science and Technology,
49, 412 (2006)
E0 ?(nhotThot)0.5
(I?2 )0.5
Data from 2000 to 2006
(I?2 )
Conversion efficiency lt10
14
Laser driven beams have excellent emission quality
Highly laminar source (virtual point source of
µm size ltlt real source)
Ultralow emittance/ virtual source
T.Cowan et al, Phys Rev Lett, 92,204851 (2004)
eN lt 0.004 mm.mrad _at_ 10 MeV 0.015 mm-mrad
_at_ 7 MeV
Mesh with 12 µm pitch
15 MeV protons

M.Borghesi et al, Phys Rev Lett., 92, 055003
(2004))
15
Rear-surface acceleration is the key to ultra-low
emittance

• High-Te, short-duration sheath
• Extremely high field (gt TV/m), and transient (1
  ps)
• Acceleration from short scale-length, cold plasma
  (at rear, non-irradiated target surface)
• Ultra-low emittance, ultra-high quality ion
  beam (approximately neutralized)

16
Modelling of currently existing data implies
acceleration time laser pulse duration
targets 25 µm Al l1 µm
Isothermal expansion model using tacc1.3 tlaser
t variable and I constant
J.Fuchs et al, Nature physics,2, 48 (2006)
Possibility of sub-ps ion bursts!!
Evidence of ps burst duration from dynamic
plasma probing
17
PIC simulations predict an excellent longitudinal
emittance,confirmed by experimental results
Rapid acceleration produces strong DE-Dt
correlation DE-Dt lt 10-6 eV-s
Energy- or time-bunching may be possible with
post-acceleration
Pulsed Accel-section
E
18
Highly charged ions are also accelerated
E.L.Clark et al., Phys. Rev. Lett., 85, 1655
(2000))
Spectra from VULCAN 100 TW Pb target irradiated
_at_ 5 1019 W/cm2

• Most of energy goes to protons
• Energy increases with charge

Contaminants
Emittance of heavy ions is also very low
19
If contaminants are removed efficiency of
heavier ion acceleration is enhanced
M. Hegelich et al., Phys. Rev. Lett. 89, 085002
(2002)
Emax gt 5MeV/nucleon 5 of laser energy
converted into high energy ions

• Cleaning methods
• target heating
• laser ablation

20
Proposed applications

• Radiography (density detection)
• Deflectometry (field mapping)
• Isochoric heating of matter (Warm Dense Matter)
• Fusion Energy (Fast Ignition)
• Injection into conventional accelerators
• Cancer therapy
• Production of isotopes for Proton Emission
  Tomography
• Industrial application (implantation,
  lithography)
• Time-resolved (lt10-12 s) ion-matter interaction
  studies

• CHALLENGES !
• Energy increase
• Monochromatic beams
• Beam transport (divergence control)
• High repetition

21
Applications pump/probe type experiments (proton
radiography/deflectometry)
Conclusion

• Operational with current
• beam parameters
• Highly transient (ps) fields
• Slow (ns) fields
• Density detection

M.Borghesi et al, Phys. Plasmas, 9, 2214 (2002)
22
Proton probing for field detection
Proton Projection Imaging
E
Proton source
Direct measurement of proton deflections, fields
mapping
Sensitive to field gradients, charge density
mapping
23
Some considerations on the diagnostic
Within a layer
Multilayer detector
t(x)
Energy
x
E
E
Source
x
Plasma
l0
Time
Source
Bragg peak deposition Broad proton spectrum
Short burst at source Time of flight dispersion
Flight time of protons along beam axis is shorter
Multiframe detection Layer n t0(En)
Temporal distortion along axis
24
High-intensity short pulse interaction Sudden
transfer of momentum and energy to fast electrons
initiates ultrafast charge dynamics

• Underdense plasmas
• Electron-ion separation due to ponderomotive
  force produces strong space-charge fields
• Radial E-fields
• Ponderomotive channeling,
• Coulomb explosion
• Longitudinal E-fields
• Wake-field, e- acceleration

• Solid targets
• Sudden release of hot electrons at front of
  target
• Space-charge E fields at target surfaces and ion
  acceleration
• B fields due to current inside target and at
  surfaces
• Effect of E and B fields on current transport

25
Solid targets Fields driving protons acceleration
L.Romagnani et al, Phys Rev Lett, 95,195001
(2005)
CPA
Longitudinal emittance (of probe beam)
DERCF0.5 MeV
p
DEDt lt 5 10-7 eV-s
Dt ps
26
Later times expanding, bell-shaped ion front
CPA
3 ps
7 ps
13 ps
17 ps
38 ps
25 ps
time
Final front velocity 3 - 4 ? 107 m/s consistent
with proton spectrum cut-off of 6-7 MeV
27
Particle tracing simulations the initial field
3-D particle tracing has been used to model the
proton probe propagation through the fields
predicted by PIC and fluid codes
Detector
x
Target
x
Data could be best reproduced with field
vanishing at finite distance from the target
Best match for hcut-off 20 µm Emax 4-5
1011 V/m
experiment
particle tracing
Passoni et al., Laser and Particle Beams 22, 163
(2004)
28
Particle tracing simulations the late times field
t 11 ps
experiment
particle tracing
Best match for Epeak 2 109 V/m, Eplateau 108
V/m
PIC fluid
E V/m
Data could only be reproduced with field peaking
at front
X microns
29
Ion bursts can be used as pumpTime-resolved
studies of of ion-driven damage of materials
Sample
H, C
laser
Creation of lattice defects old problem of
solid-state physics, never investigated for lack
of short-enough sources (ps)
EPSRC-funded TARANIS programme at QUB
30
Applications fusion energy
Conclusion

• Compression diagnosis
• Conversion efficiency
• Beam transport/focusing
• Target disassembly

M. Roth et al., Phys. Rev. Lett. 86, 436 (2001)
31
Energy production laser-driven thernonuclear
fusion
Ignition to be demostrated 2010 at NIF (US) and
MJ (France) facilities
32
Applications proton radiography
A.J.Mackinnon, P.Patel, M.Borghesi et al, PRL,
97,045001 (2005)
Cold target
Heaters 6x50J _at_ 1ns Targets 500mm 7mm and 3mm
wall
Core
Imploded
Radiography of NIF implosions requires Eproton gt
150 MeV
Moderate density (3g/cc) implosion radiographed
at RAL with 4-7 MeV protons
33
Fast Ignitor approach employs particles
accelerated by high intensity lasers
More efficient and more promising for
real energy production
34
Present assessment of proton-FI feasibility
M. Temporal, J. Honrubia, and S. Atzeni, Phys.
Plasmas 9, 3098 (2002).
Eprotons (3-10 MeV)10-20 kJ ? Elaser_required gt
100 kJ Tprotons 3-4 MeV ? Ilaser 1020
W.cm-2 tdeliverylt20 ps tlaser3-5 ps Flaser200
µm
Curved proton rich target
MeV protons
Laser
Laser

• DT fuel at 300g/cc
• 35 ?m ignition spot

? increases with Ilaser and tlaser
35
Conversion efficiency increase
Present efficiency lt 10

• Current ideas
• Optimize energy conversion into electrons (e.g.
  velvet targets, foam layers,etc...)
• Access new regimes
• Acceleration NOT driven by hot electrons
• but ponderomotively driven
• (ponderomotive regimes, laser-piston)
• Use of circular acceleration

T.Esirkepov, et al. Phys. Rev. Lett., 92, 175003
(2004)
Macchi et al, Phys. Rev. Lett., 94, 165003 (2005)
36
Applications cancer therapy
Conclusion

• Energy increase
• Monochromaticity
• Transport/focusing

S.V. Bulanov et al, Phys. Lett. A, 299, 240 (2002)
37
Applications cancer therapy
Energy requirements 50 MeV (superficial tumors)
gt 200 MeV (deep seated tumors)
Energy spread
Tipically?E/E lt 10-2
?E/E 5 may be acceptable for Intensity
Modulated Proton Therapy (e.g. Fourkal et al,
Med. Phys., 30, 1660 (2003))
Treatment dose 2 Gy/min 1-5 X1010/s
Laser- accelerators for protontherapy are
currently being considered at Fox-Chase Center
(US) National Institute for Radiological Sciences
(Japan)
38
Challenges and advantages of laser-driven approach

• CHALLENGES
• Energy increase
• Monochromatic beams
• Beam transport (divergence control)
• High repetition, stability
• Beam purity (x-rays/g-rays, electrons)

Possible advantages Reduced cost/shielding/size
possibility to avoid gantries Flexibility
(energy, type...) In-situ diagnosis Use of short
pulses?
39
Different approaches are being investigated
S.V. Bulanov et al, Phys. Lett. A, 299, 240 (2002)
Tape target
Ion beam
Laser pulse
Target chamber
T3 laser
RF cavity for phase rotation
Laser plasma ion source
2 MeV/u p (1010/sec. ) C ion (109/sec)
Energy spread 1
Injection in synchrotron
Direct irradiation(very optimistic!)
National Institute of Radiological Sciences in
Japan
40
How to increase ion energy? Optimization of
parameters from scaling laws
J. Fuchs,...M. Borghesi et al., Nature Physics 2,
48 (2006)
Target thicknesses
Thin targets are better provided contrast is high
10
4
25 µm
F10 µm
Laser pulse
10 µm
3
Laser energy in the spot (J)
10
2 µm
Prepulse
2
10
otherwise target disassembles before pulse peak
1
10
-2
-1
0
10
10
10
tlaser (ps)
41
Scaling with target thickness
ASE disruption of rear surface
25
20
Model using tacc1.3 tlaser
15
t320 fs I4 1019 W.cm-2 l1 µm
Maximum proton energy (MeV)
10
5
0
10
100
Al thickness (µm)
Similar to Kaluza, M. et al., Phys. Rev. Lett.
93, 045003 (2004) Mackinnon, A., et al., Phys.
Rev. Lett. 88, 215006 (2002).
42
Use of plasma mirror techniques may be the key
for accessing ultra-thin target regimes
1 J on target after 2 plasma mirrors Imax
1018 W.cm-2
LULI 100 TW
P.Antici et al, Phys. Plasmas (2007, in press)
30 nm SiN
30 nm SiN50 nm Al
30 nm SiN70 nm Al
ASE
ASE
For 5 µm and 10 µm thick targets, the maximum
energy is below 0.9 MeV
target
detection threshold
Electron energy in ultrathin targets is not
damped by collisions with background (cold)
electrons
0
1
2
3
4
5
6
7
8
Proton energy (MeV)
Compare with E lt1 Mev at 1018 W/cm2 without PMs
43
PIC simulations predict novel acceleration
regimes at higher intensites
T.Esirkepov, M.Borghesi, S.V.Bulanov et al. Phys.
Rev. Lett., 92, 175003 (2004)
Laser-piston regime
Radiation pressure dominates this regime of
interaction
Proton energy GeV _at_ I 1023 W/cm2
From late 2007
GEMINI facility at RAL 15 J, 30 fs, 0.5 PW 1022
W/cm2, Contrast 1010
Interferogram
Further on RAL10PW, ELI...
50 µm
Laser
Strong jets observed 50-100 ps after interaction
( 100s KeV ions)
RAL VULCAN 3 µm Al foil I 1020 W/cm2
Some experimental evidence of similar effect at
lower irradiance?
44
How to reduce spectral width ?

• Conventional approach (RF phase-space rotation)
• Demonstrated for small spectral range, can be
  extended to whole spectrum ?
• H.Daido et al, AIP Conf. Proc., 827, 2006
• Energy selection (slicing)
• Avoiding the unwanted part
• 1. Particle selection with magnetic field
  aperture
• Fourkal et al, Med. Phys., 30, 1660 (2003)
• 2. Target engineering techniques (ultrathin
  coatings, dots)
• depleting the ion layer before all the energies
  are accelerated
• 3. Laser-triggered micro-lens
• Simultaneous energy selection and
  focusing/collimation

B. M. Hegelich et al, Nature 439, 441(2006) H.
Schwoerer et al, Nature 439, 445 (2006)
45
Target engineering techniques recent
observation of monochromatic peaks
9
1
0
Double layer target High-Z bulk low-Z
mono-layer


C
5


s
i
m
u
l
a
t
e
d

P
d
2
1


s
i
m
u
l
a
t
e
d

8
1
0
-1
Monochromatic component

msr

C
5


P
d
2
2

7
1
0

P
d
4


-1

MeV
6
1
0

N
5
1
0
4
1
0
0
1
2
3
4
5

E
n
e
r
g
y


M
e
V
/
n
u
c
l
e
o
n

Energy MeV/nucleon
T. Esirkepov et al, Phys. Rev. Lett. 89, 175003
(2002).
B. M. Hegelich et al, Nature 439, 441(2006) H.
Schwoerer et al, Nature 439, 445 (2006)
46
Laser-driven micro-lens employs ps-scale
E-fields In cylindrical geometry
T.Toncian M.Borghesi, J.Fuchs et al, Science,
312, 410 (2006)
Ion transiting soon after peak of CPA2 are focused
Al
mm
1 - 6 mm
2 - 70 cm
7.6 MeV
6.25 MeV
LULI 100 TW CPA1 10 19 W/cm2 CPA2 1018 W/cm2
47
Microlens offers simultaneously collimation and
energy selection
Spectrum obtained with magnetic spex, located at
1.5 m from source
Axis of cylinder
Proton beam
Monochromatic peak!
z
Low energies
?E/E3
High energies
48
Mesh projection confirms chromatic behaviour but
also shows that beam quality is maintained
unfocused
f mm
Focused - 1 MeV
Device also suitable as a fast-switch for a
long ion pulse
E MeV
49
Laser Induceed Beams of Radiation and their
Applications
Basic Technology programme
Duration 4 years, from June 07
Collaboration
Project aims to develop target, detector and
interaction technology required for high
repetition, high energy operation of radiation
sources.
Demonstration of ion source properties suitable
for applications Development of mass-limited
target technology, debris-reduction
techniques Biological effectiveness/dose
deposition
LIBRA
Project also covers g-ray production
50
Partners on project
Queens University Belfast M.Borghesi, M.Zepf
CCLRC-STFC, RAL D.Neely, M.Tolley, J. Collier,
R. Stevens, A. Ward Strathclyde University
P.McKenna, K.Ledingham, D.Jaroszinsky, W.
Gastler Pasley University K. Spohr Imperial
College Z.Najmudin, R.Evans Southampton
University M. Kraft Surrey University K.Kirkby,
R. Webb Birmingham University B. Jones, S.
Green NPL D. DuSautoy, H.Palmans
51
LIBRA Innovative target/detector solutions

• Ultrathin targets for high-efficiency conversion
• (silicon disks, 10-30 µm diameter, 100s nm
  thick)
• Limited mass for x-ray reduction
• Mass production of targets (Silicon)
• Electrostatic injector for high repetition
  operation
• Optical tweezers for fine target positioning
• Target tracking system
• Detectors enabling fast capture and
• high-repetition operation

52
LIBRA -Optimized interaction environment and
beam characterization

• Techniques for improved laser beam profile and
  stability
• Debris removal techniques
• Low-activation environment
• Portable chamber technology

• Beam properties demonstration
• High repetition rate (reliability,
  reproducibility and debris mitigation)
• Tuneability (Source control and purity)
• Flux delivery (high integrated flux and beam
  control)

53
LIBRA - Biomedical applications
APPLICATION TESTS Work packages Biological
effects (K.Kirkby, Surrey) Dose deposition
(B.Jones, Birmingham NPL)

• Comparative studies of biological effectiveness
  and dose deposition using laser-driven ion pulses
  and conventional ion beams (micro and nano-ion
  beams)
• Biological effects of ultrashort duration
• Dose deposition studies employing laser-driven
  beams (Montecarlo modelling, human body phantoms,
  detailed dosimetry)

First project to address quantitatively
biological applications of laser-driven ions
54
Laser-driven high-energy ion sources state-of-the
-art and perspectives for applications
Conclusion

• Unique properties of laser-driven proton beams
  suggests their use in a number of important
  applications.
• Proton deflectometry/imaging is an application
  already implemented successfully with present
  beam parameters
• Other applications require performances
  exceeding present capabilities in terms of peak
  energy, energy spread, particle density
• Recent development/ current ideas, coupled to
  facility developments and recently funded
  initiatives, suggest several routes to
  aprroaching required specs in the near/medium
  term