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STUDIES OF FAST
ELECTRON
TRANSPORT VIA
PROTON

ACCELERATION AND
X
-
RAY EMISSION

Leonida A. Gizzi

ICUIL 2010,

Watkins Glen (NY)

Sept 27


Oct. 1, 2010

CONSIGLIO NAZIONALE
DELLE RICERCHE


TITLE



Introduction and motivations;



The experimental technique;



The experimental results;



Conclusions

CONTENTS

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

FIRENZE

Napoli

Lecce

Sesto F.

Pisa

Trento

Milano

Venezia

Istituto Nazionale di Ottica (INO)

THE NATIONAL INSTITUTE OF OPTICS

The Intense Laser Irrad. Lab @ INO
-
Pisa

PEOPLE


Antonio GIULIETTI (CNR)*


Leonida A. GIZZI (CNR)*


Luca LABATE (CNR)*


Petra KOESTER (CNR & Univ. of Pisa)*


Carlo A. CECCHETTI (CNR)*,


Giancarlo BUSSOLINO (CNR)


Gabriele CRISTOFORETTI (CNR)


Danilo GIULIETTI (Univ. Pisa, CNR)*


Moreno VASELLI (CNR
-
Associato)*


Walter BALDESCHI (CNR)


Antonella ROSSI (CNR)


Tadzio LEVATO (now at LNF
-
INFN)


Naveen PATHAK (UNIPI & CNR), PhD

* Also at INFN

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;

The Laboratory

The compressor


The 3TW aser

View of Lungarni

Marina di Pisa

Chiesa della Spina



HTTP://ILIL.INO.IT

On
-
line since 1998




ICF
-
RELATED AND RADIATION AND PARTICLE
SOURCES








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;

MAIN ACTIVITIES IN PROGRESS

http://www.hiperlaser.org

Participation
to ELI via
CNR and
INFN joint
participation

Participation
to HIPER via
CNR
-
CNISM
-
ENEA
coordination

Compressor

vacuum chamber

Main target

chamber

Main beam (>250 TW)

Vacuum transport line

to
SPARC

linac

Beam transport
to sparc bunker

Radiation
protection walls

GeV Electron
spectrometer

Off
-
axis
parabola

Goal: 0.9 GeV in 4 mm

See: L.A. Gizzi et al., EPJ
-
ST, 175, 3
-
10 (2009)

LASER ELECTRON ACCELERATION

250 TW system @LNF

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

S.Höfer
, T. Kämpfer,
R.Lötzsch,

I. Uschmann, E. Förster,

IOQ, Univ. Jena, Germany


F. Zamponi,
A.
Lü
bcke
,

Max Born Institute, Berlin, Germany


A. P. L. Robinson

Central Laser Facility, RAL, UK

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

Acceleration of the target
ions driven by the field
created by fast electrons

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)

Foil target

TNSA acceleration

Fast

Electrons

LASER

X
-
RAY

FLUORESCENCE

THE SIMPLE PICTURE

We use X
-
rays and
protons to reconstruct
the dynamics of fast
electron propagation
inside
the material:
here is how …

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



FAST ELECTRON PROPAGATION STUDIES

Fe

10µm

Ni

10µm

Cr

1.2µm

“Front”

pin hole camera

“Rear”

pin hole camera

Laser

80
fs; up to
0.6
J

Optical spectroscopy

Charged particle

detector

≈ 5x10
19

W/cm
2

WE USE LARGE AREA FOIL TARGETS

a)
Multi
-
layer metal ;

b)
Double layer metal
-
insulator;

c)
Single layer metal targets;

Experiments performed also at the

Jena (IOQ) JETI laser facility within the
LASERLAB access.



Laser

Radiochromic

film layers

Target

Spectrum is obtained
matching dose released in
each layer with predictions of
MC (GEANT4) through an
iterative process.

F
ORWARD ESCAPING FAST ELECTRONS



Laser

Radiochromic

film layers

Target

Forward

emitted

charged

Particles

(electrons)

F
ORWARD ESCAPING FAST ELECTRONS



Electron spectrum at E < 1MeV

Cr+Ni+Fe target

Fit with a “relativistic Maxwellian”

Yields a fast electron temperature of 160 keV

FORWARD ESCAPING FAST ELECTRONS

What about electrons inside the material?

NEW X
-
RAY IMAGING: EEPHC



L. Labate et al.,

Novel X
-
ray multi
-
spectral imaging …

Rev. Sci. Instrum.
78
, 103506 (2007)

Enables broad
-
band (≈2keV to ≈50 keV), micrometer
resolution X
-
ray imaging

Cr

Ni

Fe

LASER

≈ 5x10
19

W/cm
2



1.2
µm

10µm

10µm

MULTI
-
LAYER K
a

䥍䅇䥎G

L.A. Gizzi et al., Plasma Phys. Controll. Fusion
49
, B221 (2007)

50 µm

SINGLE LAYER METALLIC TARGET

Front and rear X
-
ray images

(TITANIUM target)

EVIDENCE OF DIRECTIONAL BREMSSTRAHLUNG

Experiment vs. model for the 5 µm thick Ti foil

F. Zamponi et al., PRL
105
, 085001 (2010)

Spectrally resolved imaging is used to identify contribution of directional
Bremstrahlung discriminating it from fluorescence k
a

emission

front

rear

Calculated
bremstrahlung
emission

Ti k
a

DIELECTRIC COATED METAL FOILS

(RCF image taken from J. Fuchs et
al., PRL 91, 255002 (2003), shot on a
100 μm glass foil)


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:













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

Targets adopted: μm thick
foils

i) single
-
layer, lacquer
-
coated

ii) multi
-
layer, lacquer
assembled

iii) single
-
layer, uncoated

Lacquer chemical composition: C
6
H
7
(NO
2
)
3
O
5


<0.6 J, 80 fs, 5E19 W/cm
2


Dielectric layers are made
using
lacquer
, an easy to use
dielectric coating characterized
by a very high resistivity (
1.5 x
10
7

W
/m)

and
high adhesion
to
the substrate;

Ti, 5 μm,
uncoated

10 μm Fe + 1.5 μm Mylar + 10
μm Ti, lacquer assembled

Fe,
10
μm,

back
-
coated with
lacquer

RCF ION DATA FROM 1
ST

EXP.


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

Smoothing of the

proton beam

Collimation of the

proton beam

Reduction of fast electron

current filamentation even after

propagation through an

insulating layer (the lacquer)

Modification of the fast electron
transverse spatial distribution with
inhibition of peripheral

portion of the fast electron current

L.A. Gizzi et al., NIM, A
620
, 83 (2010).

DEDICATED (2
ND
) EXPERIMENT


S
ystematic
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.

TARGET

5 cm

Lacquer coating

Uncoated metal

+

+

+

+

+

+

RCF

LASER

7 mm

Without dielectric

coating

EXPERIMENTAL


RCF DATA

Experimental results:
10 µm thick steel target

With lacquer

Coating (1.5 µm thick)

With lacquer

Coating (1.5 µm thick)

Without dielectric

coating

EXPERIMENTAL


RCF DATA

Experimental results:
5 µm Ti

With lacquer

Coating (1.5 µm thick)

Without dielectric

coating

EXPERIMENTAL
-

RCF DATA

Experimental results:
5 µm Ti

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

Foil target

SHEATH

Acceleration of
the target ions
driven by the
fast electrons

Fast

Electrons



LASER

X
-
RAY

FLUORESCENCE



*A. R. Bell et al., Phys. Rev. E

58
, 2471 (1998)

Propagation of a fast electron beam with angular spread, normally incident on a
resistivity gradient, gives rise to an intense magnetic field*

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 lacquer
-
coated targets.



Fast electron transport is thus investigated with the help of the
2
D
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:

5.7 μm
-
thick Al foil,

uncoated

5.7 μm
-
thick Al foil, back
-
coated with a 1.5 μm
-
thick
CH layer (
no vacuum gap
)

Transverse coordinate [μm]

Transverse coordinate [μm]

CALCULATED MAGNETIC FIELD

LASER

Simulations using LEDA* hybrid code

*A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (2007).

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;

Ti foil, 5 µm, 1.5 µm back coating

EXPERIMENTAL PROTON IMAGES

Ti foil, 5 µm, no coating

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

CONCLUSIONS


Use both X
-
ray fluorescence (k
a
⤠慮搠楯渠敭楳獩潮o瑯t
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.

THANK YOU

THE END