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Time-resolved proton probing of laserinduced front and rear side plasma expansion phenomena M. Amin1, M. Borghesi2, C. A. Cecchetti2, J. Fuchs3, M. Kalashnikov4, P. V. Nickles4, A. Pipahl1, G. Priebe5, E. Risse4, W. Sandner4,6, M. Schnürer4, T. Sokollik4, S. TerAvetisyan4, T. Toncian1, P. A. Wilson2, and O. Willi1 1Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany 2School of Mathematics and Physics, The Queen’s University Belfast BT7 1NN, UK 3Laboratoire pour l’Utilisation des Lasers Intenses, UMR 7605 CNRS-CEA-École Polytechnique-Université Paris VI, 91128 Palaiseau, France 4Max-Born-Institut, Max-Born-Str. 2a, 12489 Berlin, Germany 5CCLRC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, UK 6Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany Introduction (1) ● Short pulse (~1 ps) high power (~1018 W/cm2) laser ● Thin (~10 µm) metal target Plasma expansion on the target surface Munib Amin – ILPP Düsseldorf 2 Introduction (2) – Example ● 50 µm Ta wire, ~ 10 J, 0.4 ps 100 µm 0 ps / 3.0 ps 5.9 ps 10.1 ps ● Plasma expansion covers an area of a few square millimeters is accompanied by strong electric fields spreads along the surface on the picosecond timescale Munib Amin – ILPP Düsseldorf Experiment performed at the LULI 100TW facility 3 Introduction (3) – Benefits ● Electric fields in an expanding plasma can be used to control charged particle beams. Example: The laser proton lens* Laser pulse Focusing, energy selection Proton beam (polyenergetic, divergent) Metal foil cylinder ● A better understanding of the field evolution could allow to design new targets for beam focusing, collimation or displacement. Munib Amin – ILPP Düsseldorf *T. Toncian, et al., Science 312, 410-413 (2006). 4 How to accelerate protons ● To accelerate protons using a laser you need Thin foil target (~10 µm) A laser • with short pulse duration (about 1 ps or less) • with a high intensity (about 1019 W/cm2 or more) • that will not perturb or even burn the target before the main pulse arrives (high contrast) ● You get Proton • • • • emission from the rear side of the target Up to 1013 protons Proton energies of up to about 60 MeV A divergent proton beam of high longitudinal and transversal laminarity Small virtual source size (less than 10 µm) Munib Amin – ILPP Düsseldorf A. Maksimchuk, et al., Phys. Rev. Lett., 84, 4108-4111 (2000). R. A. Snavely, et al., Phys. Rev. Lett., 85, 2945-2948 (2000). S. P. Hatchett, et al., Phys. Plasmas 7, 2076-2082 (2000). 5 Laminarity ● Longitudinal laminarity: a class of a certain energy cannot overtake another one ● Transversal laminarity: Trajectories do not cross Proton generation foil Slow protons Fast protons Virtual source Munib Amin – ILPP Düsseldorf M. Borghesi, et al., Phys. Rev. Lett., 92, 055003 (2004). T. E. Cowan, et al., Phys. Rev. Lett., 92, 204801 (2004). 6 Probing – principle Object moving downwards ● An object varying in time can be probed by a laser generated proton beam (point projection). Munib Amin – ILPP Düsseldorf M. Borghesi, et al.,Plasma Phys. Control. Fusion 43, A267–A276 (2001). 7 Probing – electric field Higher density Displacement ++ + ● Each proton is displaced by the electric field depending on its direction of emission and its initial kinetic energy. ● The density distribution of a class of protons having the same energy is influenced in a specific way. ● Thus the temporal evolution of the electric field can be mapped. Munib Amin – ILPP Düsseldorf Lower density Higher density Proton trajectories 8 Probing – deflectometry (1) ● In proton deflectometry a mesh is projected to the detector plane. ● The green arrow identifies a certain grid node. Munib Amin – ILPP Düsseldorf 9 Probing – deflectometry (2) ● The electric fields in the plasma deflect the protons and the projection of the mesh appears distorted. ● The grid nodes can still be identified. Their displacement can be measured. Munib Amin – ILPP Düsseldorf 10 2D proton imaging – with MCP ● TiSa: 40 fs, ~ 1019 W/cm2 ● Nd:glass 1.5 ps ~1018 W/cm2 Graphics by Th. Sokollik ● magnification: ~10 ● observed area: ~3 mm ● proton energy: 1.4 - 2 MeV ● exposure time: ≤ 400 ps Munib Amin – ILPP Düsseldorf Experiment performed at the Max-Born-Institut Berlin 11 Results Region of widened mesh Image editing by Th. Sokollik Direction of the incoming laser Cross section seen by the spectrometer Shadow of the target Displaced target edge No interaction laser Munib Amin – ILPP Düsseldorf Increase of proton density along horizontal line 5J shot to the target 12 Proton Streak Camera A slit cuts out a one dimensional cross section of the obtained proton density distribution. This cross section is dispersed into a second dimension concerning the kinetic energy of the protons. Graphics by Th. Sokollik Munib Amin – ILPP Düsseldorf Experiment performed at the Max-Born-Institut Berlin 13 Image obtained using the spectrometer Glass laser shot: 0.3 J in focus, 6 x 1017 W/cm2, 1.5 ps Proton energy Slow decrease Region of high field strength No widening Protons hitting the front Munib Amin – ILPP Düsseldorf Region of increased intensity and mesh line density 14 Temporal and spatial field evolution on the target surface Laser pulse 2 RCF stack (detector) Laser pulse 1 Proton beam Metal foil cylinder Proton generation foil ● A proton beam is used to probe the electric field on the surface of a laser irradiated metal foil cylinder. ● The density distribution of the electron beam is recorded by a stack of radiochromic films. Munib Amin – ILPP Düsseldorf Experiment performed at the Vulcan Laser of the 15 Rutherford Appleton Laboratory Images obtained using the radiochromic film stack Glass laser shot: 20 J, 1.7 x 1019 W/cm2, 1.2 ps 7.32 MeV 6.48 5.55 4.48 3.14 1.06 120 300 38 ps 49 63 84 ps Munib Amin – ILPP Düsseldorf --160 12 38 2.3 18 11ps ps ps -6.8 75 ps 72 67 61 48 ps RCF calibration by Toma Toncian 16 Reconstruction of the electric field – an iterative method Experiment 1: Streaking Experiment 2: Imaging Modelling Imaging Streaking Experimental result Experimental result Parameter fit Simulation Munib Amin – ILPP Düsseldorf Parameter transfer Parameter fit Simulation 17 Comparison – simulation and experiment (1) Time of flight/ns Energy/MeV Energy/MeV Deflection on MCP/mm Time of flight/ns ● Target charge up: 10-4 C/m2 ● Decay time: 600 ps Munib Amin – ILPP Düsseldorf ● Velocity of front propagation: 1.4 x 106 m/s ● Maximum field strength: 3.75 x 108 V/m ● Decay time: 3 ps [decay ~ (1 + t / τ)-1] Image editing by Th. Sokollik 18 Comparison – simulation and experiment (2) ● Maximum field strength: 1.1 x V/m ● Propagation velocity over target surface: 0.3 x speed of light 1010 Munib Amin – ILPP Düsseldorf 7.32 MeV 6.48 5.55 4.48 3.14 1.06 19 Outlook ● Future work will concentrate on conceiving a model that bases on simulations reconstructing the plasma processes of this special phenomenon. ● Such a model might also apply to the plasma expansion inside a hollow target that is used to manipulate charged particle beams. Munib Amin – ILPP Düsseldorf 20 Thank you. Munib Amin – ILPP Düsseldorf Projects were funded by DFG TR18, GRK 1203 and 21 Laserlab Europe Modelling ● Setting up a one dimensional field configuration from simulations or previously published models or experimental results ● Setting reasonable starting parameters for the analysis of the experimental results ● Generalizing to three dimensions according to the experimental geometry Munib Amin – ILPP Düsseldorf 22 The electric field configuration ● The fraction of laser energy absorbed by hot electrons and the hot electron temperature are estimated depending on laser intensity and wave length according to Fuchs[2006]. ● The electric field is supposed to build up in a plasma expanding into vacuum as described by Mora[2003]. ● Spatial dependence in one dimension and temporal evolution are given by PIC and MHD-simulations conducted by Romagnani[2005]. Munib Amin – ILPP Düsseldorf J. Fuchs, et al., Nature Physics 2, 48-54 (2006). P. Mora, Phys. Rev. Lett. 90, 185002 (2003). L. Romagnani, et al., Phys. Rev. Lett. 95, 195001 (2005). 23 Electric field strength/(V/m) Electric field evolution – Mora field 8 3.5x10 6 0 ps 8 3.0x10 8 5 ps 8 10 ps 2.5x10 2.0x10 8 1.5x10 8 1.0x10 7 5.0x10 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 4.0x10 6 3.5x10 6 3.0x10 6 2.5x10 6 2.0x10 6 1.5x10 6 1.0x10 5 5.0x10 0.0 0.0 250 ps 500 ps 750 ps 0.2 0.4 0.6 0.8 1.0 1.2 Distance from target surface/mm Munib Amin – ILPP Düsseldorf 24 Electric field strength/(V/m) Electric field evolution – charge up 250 ps 6 8x10 6 7x10 6 6x10 6 5x10 6 4x10 6 3x10 6 2x10 6 1x10 0 0.0 500 ps 750 ps 0.2 0.4 0.6 0.8 1.0 1.2 Distance from target surface/mm Munib Amin – ILPP Düsseldorf 25 Electric field strength/(V/m) Total electric field 8 7 3.5x10 1.2x10 0 ps 8 3.0x10 250 ps 7 1.0x10 5 ps 8 2.5x10 8.0x10 10 ps 8 2.0x10 500 ps 6 750 ps 6 8 6.0x10 8 4.0x10 7 2.0x10 1.5x10 6 1.0x10 6 5.0x10 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Distance from target surface/mm Munib Amin – ILPP Düsseldorf 26 One dimensional electric field Field strength / (V/m) Position / m Time / s The field distribution according to Mora[2003] and Romagnani[2006] is modelled in one dimension. Munib Amin – ILPP Düsseldorf 27 Generalizing to more dimensions Front E E x x y Weaker and retarded The field distribution can be generalized to two or three dimensions by assuming the expansion to start later and the electron density to be lower at larger distances from the centre of the interaction. Munib Amin – ILPP Düsseldorf 28 The target geometry The one dimensional field distribution is applied along the dashed lines x t3 t2 t1 y Plain target Munib Amin – ILPP Düsseldorf Curved or cylindrical target 29 Overview ● Quasi monoenergetic particles can be generated by A special treatment of the foil target (thin layer or dots containing the particles to be accelerated on the rear surface) A second target that selects one velocity class of protons: a laser irradiated hollow metal foil cylinder ● The proton beam can be focused by using A hemispherical proton generation foil A second target that focuses the divergent proton beam: a laser irradiated hollow metal foil cylinder Munib Amin – ILPP Düsseldorf B. M. Hegelich, et al., Nature, 439, 441-444 (2006). H. Schwoerer, et al., Nature, 439, 445-448 (2006). P. K. Patel, et al., Phys. Rev. Lett. 91, 125004 (2003). T. Toncian, et al., Science 312, 410-413 (2006). 30 Overview – applications ● Medical applications Maybe one day Tumour therapy Production of radioisotopes ● ● ● ● Fast ignition Ion source for conventional particle accelerators Isochoric heating: creation of warm dense matter Diagnostics for dense plasmas: proton probing Munib Amin – ILPP Düsseldorf Routine F. Pegoraro, et al., Laser and Particle Beams, 22, 19–24 (2004). M Roth, et al., Plasma Phys. Control. Fusion, 47, B841–B850 (2005).31 P. K. Patel, et al., Phys. Rev. Lett. 91, 125004 (2003). K. W. D. Ledingham, et al., Science 300, 1107 (2003). How to accelerate protons – hot electrons + + ++ + ++ + + + + ++ + ++ + + Munib Amin – ILPP Düsseldorf Hatchett, et al., Phys. Plasmas 7, 2076 (2000). A. Pukhov, Phys. Rev. Lett., 86, 3562-3565 (2001). 32 How to accelerate protons – TNSA (Target Normal Sheath Acceleration) Munib Amin – ILPP Düsseldorf 33 Detection – radiochromic film stack RCF stack ● The density distribution of the proton beam is recorded by a stack of radiochromic films. ● Since protons deposit most of their energy in the Bragg peak, one film shows the distribution corresponding to only one specific energy. Munib Amin – ILPP Düsseldorf 34 Detection – proton streak camera (1) Top view Slit Side view Permanent magnet Detector (MCP) Munib Amin – ILPP Düsseldorf Back side – detector T. Sokollik, et al., to be published 35 Detection – proton streak camera (2) Top view ● The spectrometer setup can be used map the time evolution of an electric field in one dimension. ● In contrast to a film stack this setup provides a high energy resolution for lower energetic protons (up to ca. 5 MeV). Munib Amin – ILPP Düsseldorf Side view Back side – detector 36