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STUDIES OF FAST ELECTRON TRANSPORT VIA PROTON ACCELERATION AND X-RAY EMISSION. Title. Leonida A. Gizzi. ICUIL 2010, Watkins Glen (NY) Sept 27 – Oct. 1, 2010. CONSIGLIO NAZIONALE DELLE RICERCHE. CONTENTS. Introduction and motivations; The experimental technique;

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  1. STUDIES OF FAST ELECTRON TRANSPORT VIA PROTON ACCELERATION AND X-RAY EMISSION Title Leonida A. Gizzi ICUIL 2010, Watkins Glen (NY) Sept 27 – Oct. 1, 2010 CONSIGLIO NAZIONALE DELLE RICERCHE

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

  3. THE NATIONAL INSTITUTE OF OPTICS Istituto Nazionale di Ottica (INO) Trento Milano Venezia Sesto F. Pisa FIRENZE • 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 Napoli Lecce

  4. 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 • 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 The 3TW aser The compressor The Laboratory View of Lungarni Marina di Pisa Chiesa della Spina

  5. http://ilil.ino.it On-line since 1998

  6. http://www.hiperlaser.org Main activities in progress • 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; Participation to ELI via CNR and INFN joint participation Participation to HIPER via CNR-CNISM-ENEA coordination

  7. LASER ELECTRON ACCELERATION 250 TW system @LNF Main beam (>250 TW) Vacuum transport line to SPARC linac Beam transport to sparc bunker See presentation by L. Labate on Thursday, 11.20 – ThO7 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)

  8. http://www.hiperlaser.org 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 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

  10. 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 ⊗ Acceleration of the target ions driven by the field created by fast electrons Fast Electrons LASER We use X-rays and protons to reconstruct the dynamics of fast electron propagation inside the material: here is how … 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)

  11. FAST ELECTRON PROPAGATION STUDIES Experiments performed also at the Jena (IOQ) JETI laser facility within the LASERLAB access. • WE USE LARGE AREA FOIL TARGETS • Multi-layer metal ; • Double layer metal-insulator; • Single layer metal targets; Ni 10µm Optical spectroscopy Charged particle detector Laser 80 fs; up to 0.6 J ≈ 5x1019 W/cm2 Fe 10µm Cr 1.2µm “Rear” pin hole camera “Front” pin hole camera

  12. 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.

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

  14. FORWARD 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 What about electrons inside the material?

  15. 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)

  16. MULTI-LAYER Ka IMAGING 10µm 10µm 1.2 µm LASER ≈ 5x1019 W/cm2 Ni Fe Cr 50 µm L.A. Gizzi et al., Plasma Phys. Controll. Fusion 49, B221 (2007)

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

  18. 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)

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

  20. 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 107W/m) and high adhesion to the substrate; <0.6 J, 80 fs, 5E19 W/cm2 i) single-layer, lacquer-coated ii) multi-layer, lacquer assembled iii) single-layer, uncoated Targets adopted: μm thick foils Lacquer chemical composition: C6H7(NO2)3O5

  21. 10 μm Fe + 1.5 μm Mylar + 10 μm Ti, lacquer assembled Fe, 10 μm, back-coated with lacquer Ti, 5 μm, uncoated RCF ION DATA FROM 1ST 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).

  22. PRELIMINARY OBSERVATIONS Modification of the fast electron transverse spatial distribution with inhibition of peripheral portion of the fast electron current Collimation of the proton beam Reduction of fast electron current filamentation even after propagation through an insulating layer (the lacquer) Smoothing of the proton beam L.A. Gizzi et al., NIM, A 620, 83 (2010).

  23. 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 RCF Uncoated metal

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

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

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

  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 Propagation of a fast electron beam with angular spread, normally incident on a resistivity gradient, gives rise to an intense magnetic field* SHEATH Acceleration of the target ions driven by the fast electrons ⊗ ⊗ Fast Electrons LASER X-RAY FLUORESCENCE Foil target *A. R. Bell et al., Phys. Rev. E 58, 2471 (1998)

  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, 083105 (2007).) *A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (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: Transverse coordinate [μm] Transverse coordinate [μm] 5.7 μm-thick Al foil, back-coated with a 1.5 μm-thick CH layer (no vacuum gap) 5.7 μm-thick Al foil, uncoated

  31. CALCULATED MAGNETIC FIELD Simulations using LEDA* hybrid code LASER *A. P. L. Robinson and M. Sherlock, Phys. Plasmas 14, 083105 (2007).

  32. 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;

  33. 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.

  34. THE END THANK YOU

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