Laser-driven ion acceleration: Review of mechanisms, state of the art and applications

Transcription

1 Laser-driven ion acceleration: Review of mechanisms, state of the art and applications M.Borghesi Centre for Plasma Physics, School of Mathematics and Physics The Queen s University of Belfast Institute of Physics ASCR, ELI Beamlines institute, Prague 1 st European Advanced Accelerator Concepts Workshop La Biodola, Elba, 2-7 June 2013

2 Outline The classical mechanism Sheath acceleration (TNSA) Theoretical models/descriptions/ scaling Present status Current research trends/ developments Applications current implementation Future applications and requirements Emerging mechanisms Radiation Pressure Acceleration: Hole Boring and Light Sail Shock Acceleration Relativistic transparency regimes- Break Out Afterburner Prospects/conclusions

3 Some references / reviews A.Macchi, M. Borghesi, M. Passoni, Ion acceleration by superintense laserplasma interaction, Rev. Mod. Physics, 85, 751 (2013) H. Daido, M. Nishiuchi, and A. S. Pirozhkov, Review of laser-driven ion sources and their applications, Rep. Prog. Phys. 75, (2012) M.Borghesi, J.Fuchs, S.V. Bulanov, A.J.Mackinnon, P.Patel. M.Roth, Fast ion generation by high-intensity laser irradiation of solid targets and applications, Fusion Science and Technology, 49, 412 (2006)

4 Multi-Mev ions acceleration from the rear of thin foils was studied from ~ 2000 Clark et al, PRL, 84,670 (2000) Maksimchuk et al, PRL, 84, 4108 (2000) Snavely et al, PRL, 85,2945 (2000) Intensities rising above W/cm 2 electron acceleration to MeV energies Thin foils allow electrons to reach the rear of the target and establish a field there Protons (from contaminants) have beam features contrary to lower energy, isotropic emission previously observed from the front.

5 High density, high energy electrons lead to ultralarge field S. Wilks et al, PoP, 8, 542 (2001) n e n hot n i T hot ~ (Iλ 2 ) 0.5 At rear: ρ = en hot = en 0 exp x E = de dx = ρ 0 E(0) = ρ ε ε 0 0 dx λ D Ponderomotive electron acceleration: JxB heating From P. Gibbon, Ultraintense laser interaction with matter Typical values: λ D ~ 1 µm T h ~ MeV (Imperial College, 2005) E(0) = KT h eλ D = n hkt h ε 0 E(0) = 10 6 V 10 6 m ~ TV /m

6 Maximum TNSA energies: state of the art in 2008 M.Borghesi et al, Plasma Phys. Control.Fus., 50, (2008) Maximum proton energy [MeV] fs - 1 ps fs fs (Iλ 2 ) 0.5 Yokohama Tokyo Osaka Saclay JAEA VULCAN VULCAN MPQ Tokyo (Iλ 2 ) Lund CUOS Tokyo ASTRA VULCAN LULI LOA JanUSP NOVA PW TRIDENT RAL PW JKAREN GEMINI DRACO HERCULES GEMINI Laser, CLF, RAL: E ~ 12 J, λ = 0.8 µm, τ = 50 fs Focal spot : 3 µm FWHM Intensity~ W/cm 2 Rep rate : 1-10 second VULCAN Petawatt, λ = 1 µm, τ ~ 500 fs E = 500 J, f.s.~10 µm FWHM Intensity ~ W/cm 2 Rep rate 30 minutes LOA Salle Jaune, 800 mj, 40 fs W/cm Irradiance [W cm -2 µm 2 ] Conversion efficiency ~ few %

7 TNSA ion beam properties Low emittance: rms emittance < 0.01 π mm-mrad (0.004 mm-mrad - Cowan, PRL 2004) Short duration source: ~ 1 ps (ΔEΔt < 10-6 ev-s) High brightness: protons/ions in a single shot (> 3 MeV) High current (if stripped of electrons): ka range Divergent (~ 10s degrees) Broad spectrum Very compact: E~1-10 TV/m Acceleration lengths: ~ µm Ion beam from TARANIS facility, QUB E ~10 J on target in 10 µm spot Intensity: ~10 19 W/cm 2, duration : 500 fs Target: Al foil 10um thickness

8 Current applications of TNSA ions Ultrafast proton radiography H.Ahmed et al. Phys. Rev. Lett, 110, (2013) N.L. Kugland et al, Nature Phys, 8, 809 (2012) K.Quinn et al, Phys. Rev. Lett., 108, (2012). Warm dense matter production (isochoric heating) Ultrafast radiobiology S.D. Kraft et al, NJP, 12, (2010) A. Yogo et al, APL, 98, (2011) D. Doria et al, AIP Advances, 2, (2012) Y. Bin et al, APL,101, (2012) Interaction of ion beams with plasmas (charge exchange, stopping, etc) A.Mancic et al, Phys. Rev. Lett, 104, (2010) A. Pelka et al, Phys. RevLett., 105, (2010).. M. Gauthier, et al., Phys. Rev. Lett. 110, (2013) (Talk by S. Chen, WG2 today)

9 Prospective application requirements Fast Ignition (Inertial Confinement Fusion) 7-19 MeV protons 2-4 GeV carbon ions MeV protons Particle therapy of cancer 2-4 GeV carbon ions Typical dose fraction: 2-5 Gy 1 Gy ~ p+, ~10 9 C Particle physics applications

10 Model predictions for energy increase Fluid models (plasma expansion) P.Mora, PRL, 90, (2003) 200 Quasistatic models (test particles) J. Schreiber et al, PRL, 97, (2006) M.Passoni and M. Lontano, PRL, 101, (2008) φ * = ε e,max i ε max Maximum trapped electron energy = ZKT hot (I) ϕ 0 (ϕ * ) Empirical expression of φ*: φ * = A + Bln E L i ε max = f E L,I [ ( J) ] ( ) M.Passoni et al, New J. Phys, 12, (2010) L.Robson et al, Nature Phys.,3, 58 (2007)

11 TNSA optimization - what else can one do apart from ranking up the intensity? E(0) = n hkt h ε 0 T h ~m e c 2 1+ a ~ For a 0 >>1 Increase intensity I Aims: Increase energy Increase conversion efficiency/ion flux Strategies: Reduction of foil thickness Reduced mass targets Enhanced coupling by target structuring Enhanced electron acceleration - matching of plasma profile - grazing incidence on conical targets Enhance energy coupling into electrons Increase electron density (concentration)

12 Reduced mass target : Transverse confinement of electrons S. Buffechoux et al, Phys Rev Lett.,105, (2010) 200 µm LULI, 100 TW, I~ W/cm 2 Targets as small as 20 µm x 20 µm were used L.Romagnani et al, PRL, 95, (2005) Confirmed by O. Tresca et al PPCF, 53, (2011) (also F. Kroll s talk- WG2)

13 Enhanced acceleration from conical target S. Gaillard et al, Phys. Plasmas, 18, (2011) T.Kluge et al, NJP, 14, (2012) Principle magnetized plasma More efficient coupling into hot electrons due to interaction with walls (direct electron acceleration) Reference planar foil Best conical target results Trident laser, 80 J, 700 fs

14 Optimized TNSA in structured targets D. Margarone et al, PRL,109, (2012) I ~ W/cm 2 30 fs, 2 µm f.s. High Contrast: 5 -10ps Other approaches: Foam layers, controlled preplasmas Best results at intermediate diameter of spheres (535 nm) which optimize absorption

15 Emerging acceleration mechanisms Radiation Pressure Acceleration Hole Boring Light Sail T. Esirkepov et al, PRL (2004) Shock acceleration L. Silva et al, PRL (2004) Break-out Afterburner Relativistic transparency L. Yin, et al., Phys. Rev. Lett. 107, (2011)

16 Radiation pressure in laser matter interaction Radiation pressure upon light reflection from a mirror surface: p R = 2I L c In a plasma the effect is felt by the electrons via the ponderomotive force f p = m 4 x v 2 os(x) ( 1 cos2ω 0 t) P L = Wcm -2 Non-oscillating term Oscillating term Steady pressure, JXB heating, transferred to ions via space-charge hot electrons compression region E ~ 2I/nc depletion region 30fs 60fs Ions are pushed into overdense plasma Hole boring S. Wilks et al,prl 68, 1383 (1992)

17 Monochromatic proton beams due to HB acceleration C.A. Palmer et al, Phys. Rev. Lett, 106, (2011) IC/BNL collaboration C0 2 laser, 0.5 TW, 5 ps, I ~ W/cm 2 Circularly polarized Hydrogen gas jet, n ~ cm W/cm 2 Liquid hydrogen target A.Robinson PPCF 2009

18 Shock acceleration L.Silva et al, PRL 92, (2004) D.Haberberger et al, Nature Phys., 8, 95 (2012) Laser piston launches high Mach number electrostatic shock into an overdense plasma The propagating electrostatic structure reflects ions in the target to v ~2 v s Monochromatic proton peaks observed in experiments using overdense gas jet with C W/cm 2 (UCLA) Theory suggests plasma heating is a requirement in stable shock formation: see also A.Macchi et al, Phys. Rev. E,2012

19 Alternative approach: collisionless shocks in exploding foils Thin foils exploded by ASE Controlled prepulse TITAN LLNL Courtesy of J. Fuchs (unpublished)

20 Radiation Pressure applied to thin foils - light sail Z + e- Cyclical re-acceleration of ions Narrow-band spectrum (whole-foil acceleration) Fast scaling with intensity Issues at present intensities Competition with TNSA Hot electron heating cause foil disassembly (ultrathin foils are needed for moderate a 0 ) F R = (1+ R)A I L c (1+ R)τ I v i = L m i n i d c Iτη 1 η = m i n i d Areal density Use of circular polarization: No JxB acceleration No TNSA No target heating Quasi-static pressure drive E ions ~ ( I τ η) 2 T.Esirkepov, et al. Phys. Rev. Lett., 92, (2004) APL Robinson et al, NJP, 10, (2009)

21 Radiation pressure acceleration with 10 PW pulses: GeV energies at W/cm 2 B. Qiao et al, Phys Rev Lett,102, (2009) Unstable case 30 n c 100 n Stable acceleration requires smooth transition c between Unstable hole case boring phase and LS phase W/cm 2 RP A.P.L. in phase Robinson 1: 2I/c et Χ (1-v al, b /c)/(1+v b /c) RP NJP in phase (2009) 2: 2I/c Χ (1-v i /c)/(1+v i /c) Need to drive target quite hard to achieve a h ILLUMINATION hole-boring 2D PIC velocity code (M. (v b ~c) Geissler) before transition

22 In multi-species targets the acceleration of the lighter species is inherently more stable B. Qiao et al, PRL, 105, (2010) T.Pu Yu et al, PRL, 105, (2010) Nanofoil target: electron density n e0 =200n c, thickness l 0 =8nm<l s C 6+ and H + : n ic0 =32.65 n c, n ip0 =4.1n c with n ic0 :n ip0 =8:1 I 0 ~ W/cm 2, 40 laser cycles, λ= 1 µm Electrons C6+ H+ The C 6+ layer has insufficient charge-balancing electronsdebunching the proton layer moves ahead of the C 6+ layer. Debunching of the electron layer - complete separation of the C 6+ and proton layers. Strong electron leakage Proton layer is surrounded by an excess number of electrons--->stable bunching

23 RPA features emerging on VULCAN Petawatt experiments using thin metallic targets S. Kar et al, Phys. Rev. Lett, 109, (2012) 100nm Cu Linear Pol I = 3 x W/cm 2 Protons 700 fs, 400 J, I > W/cm 2 Solid line: TP1 spectrum (laser axis) Dotted line: TP2 spectrum (13º) Targets thicker than 0.5 µm show standard continuous, exponential spectra Peaks observed regardless of laser polarization - Hybrid scheme where TNSA and RPA cohesist Theory descrived in B. Qiao et al, PRL, 108, (2012)

24 Scaling of carbon peak with Light sail parameter ( I τ η) 2 ( I τ η) 2 Energy of peak scales ~ I τ η ( ) 2 Henig, PRL (2009) Up to 20 Mev/nucleon in more recent campaigns Multispecies acceleration with RPA features also investigated by S.Steinke et al, Phys. Rev. ST,16, (2013) B. Aurand et al, NJP,15, (2013) (talk WG2)

25 Scaling highly promising for progress toward ion energies on 10 PW systems S. Kar et al, Phys. Rev. Lett, 109, (2012) Inset : PIC simulation scaled up from VULCAN data (2 X I, 1/2.5 target areal density) Red dots: 2D and 3D PIC results from multispecies simulations of stable RPA taken from literature

26 Slides from D.Jung Target Laser Ions t 1 t 2 Talk by D. Jung, WG2 Yin, et al., Laser and Particle Beams 24 (2006), 1 8 Albright, et al., Phys. Plasmas 14, (2007) Yin, et al., Phys. Plasmas 14, , (2007) Yin, et al., Phys. Rev. Lett. 107, (2011) Yin, et al., Phys. Plasmas 18, (2011) LA-UR

27 Thickness scan carbon C 6+ Thickness scan carbon H + Application to neutron production (talk by M. Roth, WG2) M.Roth et al, PRL,110, (2013) Optimum diamond thickness for Trident at ~200nm will change with intensity & contrast level B. Hegelich, et al., Nucl. Fusion 51, (2011) D.Jung et al, NJP, 15, (2013) Conversion Collimated efficiency: neutron flux 6=8% at high energy LA-UR

28 Summary / perspective Taking 200 MeV/nucleon as projected milestone: TNSA: scaling predictions (PIC): 200 Iλ 2 ~ mid W/cm 2 for ps pulses ~ for 30 fs pulses Endpoint in the spectrum - not many particles. BOA: More efficient heating, 200 MeV may be Iλ 2 ~ W/cm 2 for 0.5 ps pulses (?) Endpoint in the spectrum few particles. RPA HB: E ion ~ Iλ 2 /n. decreasing density helps- operating below γn c, may make 200 few W/cm 2 feasible --- dense ion bunch, monochromatic (e.g. A.P.L. Robinson, PoP, 18, , 2011) RPA LS: E ion ~ (Iτ /(nd)) 2, multispecies for better stabilization 200 MeV possible at few W/cm 2 if drive on suitably thin foil can be stabilized (loose focusing, multi PW beam) Dense bunch, monochromatic Conclusion.PW systems with ultrafast focusing or, even better, multi PW systems (Apollon, ELI ) needed for further progress

29 Acknowledgements Contributions from: A. Macchi, Pisa University M. Passoni, Politecnico Milano D. Jung, Queen s University Belfast J. Fuchs, LULI- Ecole Polytechnique