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Presentation on theme: "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."— Presentation transcript:


2 Introduction and motivations; The experimental technique; The experimental results; Conclusions CONTENTS

3 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

4 The Intense Laser Irrad. INO-Pisa PEOPLE 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 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

5 On-line since 1998

6 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 Participation to ELI via CNR and INFN joint participation Participation to HIPER via CNR- CNISM- ENEA coordination

7 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) See presentation by L. Labate on Thursday, – ThO7 LASER ELECTRON ACCELERATION 250 TW

8 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

9 COLLABORATION S.Höfer, T. Kämpfer, R.Lötzsch, I. Uschmann, E. Förster, IOQ, Univ. Jena, Germany F. Zamponi, A.Lu ̈ 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

10 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 (2005). S. Betti et al., Plasma Phys. Contr. Fusion 47, (2005). J. Fuchs et al. Nature Physics 2, 48 (2006). X.H.Yuan et al., New Journal of Physics (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 ⊗

11 FAST ELECTRON PROPAGATION STUDIES Fe 10µm Ni 10µm Cr 1.2µm “Front” pin hole camera “Rear” pin hole camera Laser80 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.

12 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

13 Laser Radiochromic film layers Target Forward emitted charged Particles (electrons) FORWARD ESCAPING FAST ELECTRONS

14 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?

15 NEW X-RAY IMAGING: EEPHC L. Labate et al., Novel X-ray multi-spectral imaging … Rev. Sci. Instrum. 78, (2007) Enables broad-band (≈2keV to ≈50 keV), micrometer resolution X-ray imaging

16 Cr Ni Fe LASER ≈ 5x10 19 W/cm µm 10µm MULTI-LAYER K  IMAGING L.A. Gizzi et al., Plasma Phys. Controll. Fusion 49, B221 (2007) 50 µm

17 SINGLE LAYER METALLIC TARGET Front and rear X-ray images (TITANIUM target)

18 EVIDENCE OF DIRECTIONAL BREMSSTRAHLUNG Experiment vs. model for the 5 µm thick Ti foil F. Zamponi et al., PRL 105, (2010) Spectrally resolved imaging is used to identify contribution of directional Bremstrahlung discriminating it from fluorescence k  emission Calculated bremstrahlung emission Ti k 

19 DIELECTRIC COATED METAL FOILS (RCF image taken from J. Fuchs et al., PRL 91, (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, (2002), shot on a 100 μm plastic foil).

20 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  /m) and high adhesion to the substrate;

21 Ti, 5 μm, uncoated 10 μm Fe 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, (2009).

22 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).

23 DEDICATED (2 ND ) 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

24 Without dielectric coating EXPERIMENTAL – RCF DATA Experimental results: 10 µm thick steel target With lacquer Coating (1.5 µm thick)

25 With lacquer Coating (1.5 µm thick) Without dielectric coating EXPERIMENTAL – RCF DATA Experimental results: 5 µm Ti

26 With lacquer Coating (1.5 µm thick) Without dielectric coating EXPERIMENTAL - RCF DATA Experimental results: 5 µm Ti

27 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.

28 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*

29 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 2D hybrid Vlasov-Fokker-Planck (VFP) numerical Code LEDA (A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, (2007).) *A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, (2007).

30 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]

31 CALCULATED MAGNETIC FIELD LASER Simulations using LEDA* hybrid code *A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, (2007).

32 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

33 CONCLUSIONS 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.



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