STUDIES OF FAST ELECTRON TRANSPORT VIA PROTONACCELERATION 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

TrentoMilano

Venezia

Istituto Nazionale di Ottica (INO)Istituto Nazionale di Ottica (INO)THE NATIONAL INSTITUTE OF OPTICS

The Intense Laser Irrad. Lab @ INO-PisaThe Intense Laser Irrad. Lab @ INO-PisaThe Intense Laser Irrad. Lab @ INO-PisaThe Intense Laser Irrad. Lab @ INO-Pisa

PEOPLEPEOPLE• Antonio GIULIETTI (CNR)*Antonio GIULIETTI (CNR)*• Leonida A. GIZZI (CNR)* Leonida A. GIZZI (CNR)* • Luca LABATE (CNR)*Luca LABATE (CNR)*• Petra KOESTER (CNR & Univ. of Pisa)*Petra KOESTER (CNR & Univ. of Pisa)*• Carlo A. CECCHETTI (CNR)*,Carlo A. CECCHETTI (CNR)*,• Giancarlo BUSSOLINO (CNR)Giancarlo BUSSOLINO (CNR)• Gabriele CRISTOFORETTI (CNR)Gabriele CRISTOFORETTI (CNR)• Danilo GIULIETTI (Univ. Pisa, CNR)*Danilo GIULIETTI (Univ. Pisa, CNR)*

• Moreno VASELLI (CNR-Associato)*Moreno VASELLI (CNR-Associato)*

• Walter BALDESCHI (CNR)Walter BALDESCHI (CNR)

• Antonella ROSSI (CNR)Antonella ROSSI (CNR)• Tadzio LEVATO (now at LNF-INFN)Tadzio LEVATO (now at LNF-INFN)• Naveen PATHAK (UNIPI & CNR), PhDNaveen PATHAK (UNIPI & CNR), PhD

* Also at INFN* Also at INFN

CNR - DIPARTIMENTO MATERIALI E DISPOSITIVI (Dir. M. Inguscio)CNR - DIPARTIMENTO MATERIALI E DISPOSITIVI (Dir. M. Inguscio)Progetto: OPTICS, PHOTONICS AND PLASMAS (Resp. S. De Silvestri)Progetto: OPTICS, PHOTONICS AND PLASMAS (Resp. S. De Silvestri)Unit (Commessa): HIGH FIELD PHOTONICS (Head: Leo A. Gizzi)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 PisaChiesa della Spina

HTTP://ILIL.INO.ITHTTP://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 PROGRESSMAIN 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 targetchamber

Main beam (>250 TW)Vacuum transport lineto 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)

See presentation by L.

Labate on Thursday, 11.20

– ThO7

See presentation by L.

Labate on Thursday, 11.20

– ThO7

LASER ELECTRON ACCELERATION

250 TW system @LNF

ONGOING HIPER RELATED ACTIVITY

PARTICIPATION TO HIPER EXPERIMENTAL ROADMAP;COORDINATION OF FACILITY DESIGN

•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.Lubcke, Max Born Institute, Berlin, Germany

A. P. L. RobinsonCentral 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 ElectronsLASER

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

Fe10µm

Ni10µm

Cr1.2µm

“Front” pin hole camera

“Rear” pin hole camera

Laser 80 fs; up to 0.6 J

Optical spectroscopy

Charged particledetector

≈ 5x1019 W/cm2

WE USE LARGE AREA FOIL TARGETSa)Multi-layer metal ;b)Double layer metal-insulator;c)Single layer metal targets;

Experiments performed also at theJena (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.

FORWARD ESCAPING FAST ELECTRONS

Laser

Radiochromic film layers

Target

Forward emitted charged Particles(electrons)

FORWARD ESCAPING FAST ELECTRONS

Electron spectrum at E < 1MeV

0 1 005 1 071 1 081 .5 1 082 1 082 .5 1 083 1 0802 0 04 0 06 0 08 0 01 0 0 0E le c tro n s (e M e V -1 c m-2)E n e rg y (k e V )y = m 1 *m 0 * e x p (-(m 0 + m 2 )/m 3 )E rro rV a lu e1 .4 0 0 9 e + 1 21 .5 7 3 8 e + 0 5m 1 1 .4 3 5 e + 0 9-4 8 3 .0 2m 2 2 7 .4 4 51 6 1 .3 3m 3 N A1 .1 8 3 6 e + 1 6C h is qN A0 .8 7 8 2 2R Cr+Ni+Fe target

0 100

5 107

1 108

1.5 108

2 108

2.5 108

3 108

0 200 400 600 800 1000

Energy (keV)

y = m1*m0* exp(-(m0+m2)/m3)ErrorValue

1.4009e+121.5738e+05m1 1.435e+09-483.02m2

27.445161.33m3 NA1.1836e+16ChisqNA0.87822R

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: EEPHCNEW 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

FeLASER

≈ 5x1019 W/cm2

1.2

µm

10µ

m

10µ

m

MULTI-LAYER K IMAGING

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

50 µm

SINGLE LAYER METALLIC TARGET SINGLE LAYER METALLIC TARGET

Front and rear X-ray images

(TITANIUM target)

EVIDENCE OF DIRECTIONAL BREMSSTRAHLUNGEVIDENCE 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 emission

Calculated bremstrahlung emission

Ti k

DIELECTRIC COATED METAL FOILSDIELECTRIC 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 TARGETSIONS FROM LAYERED TARGETS

Targets adopted: μm thick foils

i) single-layer, lacquer-coatedii) multi-layer, lacquer assemblediii) single-layer, uncoated

Lacquer chemical composition: C6H7(NO2)3O5

<0.6 J, 80 fs, 5E19 W/cm2

Dielectric layers are made using lacquer, an easy to use dielectric coating characterized by a very high resistivity (1.5 x 107 /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 1RCF ION DATA FROM 1STST EXP. 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 OBSERVATIONSPRELIMINARY OBSERVATIONS

Smoothing of the proton beam

Collimation of the proton beam

Reduction of fast electroncurrent filamentation even after

propagation through an insulating layer (the lacquer)

Modification of the fast electron transverse spatial distribution with

inhibition of peripheralportion of the fast electron current

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

DEDICATED (2DEDICATED (2NDND) EXPERIMENT) 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.

TARGET

5 cm

Lacquer coating

Uncoated metal

+

+

+

+

+

+

RCF

LASER

7 mm

Without dielectriccoating

EXPERIMENTAL – RCF DATAEXPERIMENTAL – RCF DATA

Experimental results: 10 µm thick steel target

With lacquer Coating (1.5 µm thick)

With lacquer Coating (1.5 µm thick)

Without dielectriccoating

EXPERIMENTAL – RCF DATAEXPERIMENTAL – RCF DATA

Experimental results: 5 µm Ti

With lacquer Coating (1.5 µm thick)

Without dielectriccoating

EXPERIMENTAL - RCF DATAEXPERIMENTAL - RCF DATA

Experimental results: 5 µm Ti

EXPERIMENTAL OBSERVATIONSEXPERIMENTAL 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-INSULATORTHE 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 APPROACHMODELLING 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 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. PROFILECALCULATED 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 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 IMAGESEXPERIMENTAL 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

CONCLUSIONSCONCLUSIONS

Use both X-ray fluorescence (k) 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.

THANK YOUTHANK YOU

THE END