Transcript Diapositiva 1

STUDIES OF FAST
ELECTRON
TRANSPORT VIA
PROTON
ACCELERATION AND
TITLE
X-RAY EMISSION
Leonida A. Gizzi
ICUIL 2010,
Watkins Glen (NY)
Sept 27 – Oct. 1, 2010
CONSIGLIO NAZIONALE
DELLE RICERCHE
CONTENTS
• Introduction and motivations;
• The experimental technique;
• The experimental results;
• Conclusions
THE NATIONAL INSTITUTE OF OPTICS
Istituto Nazionale di Ottica (INO)
Trento
Milano
Venezia
Sesto F.
Pisa
FIRENZE
Napoli
Lecce
U.O.S. INO-CNR
 Firenze, Polo Scientifico Sesto
Fiorentino
 Trento, “BEC centre”
 Pisa, “Adriano Gozzini”
Area della Ricerca CNR di Pisa
 Napoli, Area della Ricerca CNR di
Pozzuoli
 Lecce, Arnesano
The Intense Laser Irrad. Lab @ INO-Pisa
CNR - DIPARTIMENTO MATERIALI E DISPOSITIVI (Dir. M. Inguscio)
Progetto: OPTICS, PHOTONICS AND PLASMAS (Resp. S. De Silvestri)
Unit (Commessa): HIGH FIELD PHOTONICS (Head: Leo A. Gizzi)
High field photonics for the generation of ultrashort radiation pulses
and high energy particles;
Development of broadband laser amplifiers for stategic studies on
Inertial Confinement Fusion;
PEOPLE
•
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•
•
•
•
•
•
Antonio GIULIETTI (CNR)*
Leonida A. GIZZI (CNR)*
Luca LABATE (CNR)*
Petra KOESTER (CNR & Univ. of Pisa)*
Carlo A. CECCHETTI (CNR)*,
Giancarlo BUSSOLINO (CNR)
The 3TW aser
Gabriele CRISTOFORETTI (CNR)
Danilo GIULIETTI (Univ. Pisa, CNR)*
Moreno VASELLI (CNR-Associato)*
The compressor
The Laboratory
• Walter BALDESCHI (CNR)
• Antonella ROSSI (CNR)
• Tadzio LEVATO (now at LNF-INFN)
• Naveen PATHAK (UNIPI & CNR), PhD
* Also at INFN
View of Lungarni
Marina di Pisa
Chiesa della Spina
HTTP://ILIL.INO.IT
On-line since 1998
MAIN ACTIVITIES IN PROGRESS
•ICF-RELATED AND RADIATION AND PARTICLE
SOURCES
Participation
Participation
to ELI via
to HIPER via
CNR and
CNRINFN joint
CNISMparticipation
ENEA
coordination
http://www.hiperlaser.org
• High-gradient, laser-plasma acceleration in gases;
• Ultrafast optical probing of plasma formation at ultra-high intensities;
• X-ray diagnostics for advanced spectral/spatial investigation;
• Ultraintense laser-foil interactions for X-ray and ion acceleration;
LASER ELECTRON ACCELERATION
250 TW system @LNF
Main beam (>250 TW)
Vacuum transport line
to SPARC linac
Beam transport
to sparc bunker
Radiation
protection walls
GeV Electron
spectrometer
Main target
chamber
Compressor
vacuum chamber
Off-axis
parabola
Goal: 0.9 GeV in 4 mm
See: L.A. Gizzi et al., EPJ-ST, 175, 3-10 (2009)
ONGOING HIPER RELATED
ACTIVITY
PARTICIPATION TO HIPER EXPERIMENTAL ROADMAP;
COORDINATION OF FACILITY DESIGN
http://www.hiperlaser.org
•Fast electron generation and transport measurements;
•Laser-plasma interaction studies in a shock-ignition relevant conditions;
ILIL Experiments (PI) at RAL(UK), PALS (CZ), JETI(IOQ, D)
+ collaborations at TITAN, OMEGA-EP - F. Beg
COLLABORATION
L.A. Gizzi, S. Betti, A. Giulietti, D. Giulietti, P. Koester, L. Labate, T. Levato*
ILIL, IPCF-CNR and INFN, Pisa, Italy, * LNF-INFN, Frascati, Italy
S.Höfer, T. Kämpfer, R.Lötzsch, I. Uschmann, E. Förster,
IOQ, Univ. Jena, Germany
F. Zamponi, A.Lübcke,
Max Born Institute, Berlin, Germany
A. P. L. Robinson
Central Laser Facility, RAL, UK
THE SIMPLE PICTURE
Laser-foil interactions creates huge currents of relativistic eletrons propagating
in the solid and giving rise to intense X-ray emittion and, ultimately, ion
emission from the rear surface of the foil
TNSA acceleration
⊗
LASER
Fast
Electrons
X-RAY
FLUORESCENCE
Foil target
R.A.Snavely et al., Phys. Rev. Lett. 85, 2945 (2000)
L. Romagnani et al., Phys. Rev. Lett. 95 195001 (2005).
S. Betti et al., Plasma Phys. Contr. Fusion 47, 521-529 (2005).
J. Fuchs et al. Nature Physics 2, 48 (2006).
X.H.Yuan et al., New Journal of Physics 12 063018 (2010)
Acceleration of the target
ions driven by the field
created by fast electrons
We use X-rays and
protons to reconstruct
the dynamics of fast
electron propagation
inside the material:
here is how …
FAST ELECTRON PROPAGATION STUDIES
Experiments performed also at the
Jena (IOQ) JETI laser facility within the
LASERLAB access.
Ni
10µm
WE USE LARGE AREA FOIL TARGETS
a)Multi-layer metal ;
b)Double layer metal-insulator;
c)Single layer metal targets;
Optical spectroscopy
Charged particle
detector
Laser
80 fs; up to 0.6 J
≈ 5x1019 W/cm2
Fe
10µm
“Rear”
pin hole camera
Cr
1.2µm
“Front”
pin hole camera
FORWARD ESCAPING FAST ELECTRONS
Target
Radiochromic
film layers
Laser
Spectrum is obtained
matching dose released in
each layer with predictions of
MC (GEANT4) through an
iterative process.
FORWARD ESCAPING FAST ELECTRONS
Target
Radiochromic
film layers
Laser
Forward
emitted
charged
Particles
(electrons)
FORWARD ESCAPING FAST ELECTRONS
Electron spectrum at E < 1MeV
-2
Electrons (e MeV cm )
Cr+Ni+Fe target
3 108
2.5 108
-1
y = m1*m0* exp(-(m0+m2)/m3)
Value
Error
m1
1.5738e+05
1.4009e+12
m2
-483.02
1.435e+09
m3
161.33
27.445
Chisq
1.1836e+16
NA
R
0.87822
NA
2 108
1.5 108
Fit with a “relativistic Maxwellian”
8
1 10
5 107
Yields a fast electron temperature of 160 keV
0 100
0
200
400
600
800
1000
Energy (keV)
What about electrons inside the material?
NEW X-RAY IMAGING: EEPHC
Enables broad-band (≈2keV to ≈50 keV), micrometer
resolution X-ray imaging
L. Labate et al., Novel X-ray multi-spectral imaging …
Rev. Sci. Instrum. 78, 103506 (2007)
10µm
10µm
Ni
Fe
LASER
≈ 5x1019 W/cm2
Cr
1.2 µm
MULTI-LAYER Ka IMAGING
50 µm
L.A. Gizzi et al., Plasma Phys. Controll. Fusion 49, B221 (2007)
SINGLE LAYER METALLIC TARGET
(TITANIUM target)
Front and rear X-ray images
EVIDENCE OF DIRECTIONAL BREMSSTRAHLUNG
Spectrally resolved imaging is used to identify contribution of directional
Bremstrahlung discriminating it from fluorescence ka emission
front
Ti ka
rear
Calculated
bremstrahlung
emission
Experiment vs. model for the 5 µm thick Ti foil
F. Zamponi et al., PRL 105, 085001 (2010)
DIELECTRIC COATED METAL FOILS
Plastic coatings have been found to induce filamentation of the fast
electron current. Such effect has a strong detrimental influence on the ion
bunch cross section by increasing its size and depleting its uniformity:
(RCF image taken from J. Fuchs et
al., PRL 91, 255002 (2003), shot on a
100 μm glass foil)
Experimentally, fast electron current filamentation has been observed to
occur with plastic coatings thicker than 0.1 μm (M. Roth et al., PRST-AB 5,
061301 (2002), shot on a 100 μm plastic foil).
IONS FROM LAYERED TARGETS
Dielectric layers are made
using lacquer, an easy to use
dielectric coating characterized
by a very high resistivity (1.5 x
107 W/m) and high adhesion to
the substrate;
<0.6 J, 80 fs, 5E19 W/cm2
i) single-layer, lacquer-coated
Targets adopted: μm thick
ii) multi-layer, lacquer
foils
assembled
iii) single-layer, uncoated
Lacquer chemical composition: C6H7(NO2)3O5
RCF ION DATA FROM 1ST EXP.
Ti, 5 μm,
uncoated
10 μm Fe + 1.5 μm Mylar + 10
μm Ti, lacquer assembled
Fe, 10 μm,
back-coated with
lacquer
Given their more favourable charge-to-mass ratio, ion bunch mainly consists
of protons;
Energy ranges between 1.2 and 3.5 MeV (from a radiographic image of a Ta
grid & SRIM calculations), confirmed by 1D, PIC model simulations;
Dielectric coatin collimates and smooths proton beam;
Protons consistently originate from the lacquer layer, even if lacquer is buried
in the target;
S. Betti et al., On the effect of rear-surface dielectric coatings on laser-driven
proton acceleration Phys. Plasmas, 16, 100701 (2009).
PRELIMINARY OBSERVATIONS
Collimation of the
proton beam
Smoothing of the
proton beam
Modification of the fast electron
transverse spatial distribution with
inhibition of peripheral
portion of the fast electron current
Reduction of fast electron
current filamentation even after
propagation through an
insulating layer (the lacquer)
L.A. Gizzi et al., NIM, A 620, 83 (2010).
DEDICATED (2ND) EXPERIMENT
Systematic comparison between the ion bunches
emitted from uncoated and lacquer-coated metal foils.
Same experimental setup of the first campaign
Targets: 10 μm thick steel and 5 μm thick Ti foils, either
uncoated or back-coated with 1.5 µm thick lacquer.
7 mm
LASER
TARGET
+
+
+
+
+
+
Lacquer coating
5 cm
Uncoated metal
RCF
EXPERIMENTAL – RCF DATA
Experimental results: 10 µm thick steel target
Without dielectric
coating
With lacquer
Coating (1.5 µm thick)
EXPERIMENTAL – RCF DATA
Experimental results: 5 µm Ti
Without dielectric
coating
With lacquer
Coating (1.5 µm thick)
EXPERIMENTAL - RCF DATA
Experimental results: 5 µm Ti
Without dielectric
coating
With lacquer
Coating (1.5 µm thick)
EXPERIMENTAL OBSERVATIONS
Dielectric coating increases collimation and uniformity of the proton
beam;
In contrast with previous experiments that show that dielectric coatings
thicker than 0.1 μm induce fast electron current filamentation with
detrimental effect on uniformity of the accelerated proton bunch;
As in the TNSA scenario (which is here the key mechanism) ion
acceleration is driven by the fast electron current, the observations
suggest that modification in the fast electron transport regime;
The different quality/type of dielectric coating (plastic vs. lacquer) and
the quality of the coating-metal interface adopted here might played a
role. Indeed, standard plastic-coated foils (vacuum deposition) may
include uncontrolled vacuum gaps and loose interfaces.
THE MODEL FOR A METAL-INSULATOR
Propagation of a fast electron beam with angular spread, normally incident on a
resistivity gradient, gives rise to an intense magnetic field*
⊗
LASER
⊗
SHEATH
Fast
Electrons
X-RAY
FLUORESCENCE
Foil target
*A. R. Bell et al., Phys. Rev. E 58, 2471 (1998)
Acceleration of
the target ions
driven by the
fast electrons
MODELLING APPROACH
A full modeling of our proton acceleration conditions, including
fast electron generation and transport is well beyond the possibility
of presently available numerical codes.
Since the emphasis is on the comparison of two configurations
with identical laser-target interaction conditions, we can focus
on the fast electron transport stage in order to find the possible
origine of differences observed between uncoated and lacquercoated targets.
Fast electron transport is thus investigated with the help of the 2D
hybrid Vlasov-Fokker-Planck (VFP) numerical Code LEDA (A. P. L.
Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (2007).)
*A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (2007).
CALCULATED F.E. PROFILE
LEDA results for the fast electron distribution on the
back of the target after the laser-matter interaction stage:
Transverse coordinate [μm]
5.7 μm-thick Al foil,
uncoated
Transverse coordinate [μm]
5.7 μm-thick Al foil, backcoated with a 1.5 μm-thick
CH layer (no vacuum gap)
CALCULATED MAGNETIC FIELD
Simulations using LEDA* hybrid code
LASER
*A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (2007).
EXPERIMENTAL PROTON IMAGES
Simulation predict a fine scale filamentation of the fast electron beam – similar
features are observed in our experimental data; with the dielectric layer on, the
filamentation is suppressed and the f.e. beam is strongly modified
Ti foil, 5 µm, no coating
Ti foil, 5 µm, 1.5 µm back coating
Effect may originate from the onset of a large scale quasi-static B-field
at the interface due to the resistivity gradient in the dielectric;
CONCLUSIONS
Use both X-ray fluorescence (ka) and ion emission to
investigate fast electron transport inside layered targets;
Evidence of directional Bremstrahlung from fast electrons
using novel broad-band spectrally resolved X-ray imaging;
Proton bunch collimation and better uniformity observed from
lacquer-coated metal targets;
Resistivity gradient leads to a magnetic field that appears to
collimate f.e. and suppress fine scale filamentation.
THE END
THANK YOU