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Laser-Ion Acceleration with the Leaky Light Sail

Laser-Ion Acceleration with the Leaky Light Sail. Bin Qiao , Anupam Karmakar , Paul Gibbon , J ü lich Supercomputing Centre. EMMI Workshop, Speyer, 27 September 2010. Forschungszentrum Jülich (FZJ). TEXTOR. JSC. COSY. Plasma Simulation Lab at JSC. Staff Lukas Arnold

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Laser-Ion Acceleration with the Leaky Light Sail

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  1. Laser-Ion Acceleration with the Leaky Light Sail Bin Qiao, AnupamKarmakar, Paul Gibbon, Jülich Supercomputing Centre EMMI Workshop, Speyer, 27 September 2010

  2. Forschungszentrum Jülich (FZJ) TEXTOR JSC COSY

  3. Plasma Simulation Lab at JSC • Staff • Lukas Arnold • AnupamKarmakar • Bin Qiao (AvH) • Paul Gibbon • Students • Benjamin Berberich (Ph.D., IEF-4) • Andreas Galonska (Ph.D.) • HelgeHübner (Master) • Robert Speck (Ph.D.) • Mathias Winkel (Ph.D.) • Andreas Breslau (Dipl., U. Köln)

  4. Target normal sheath acceleration (TNSA) Wilks et al., PoP (2001) • Linearly polarized laser • Electrons heated to MeV temperature via j xB force • Ions accelerated mainly off target rear • Low beam density, large divergence, broad energy spread ! • Variations: microdots; double layers; oblique incidence; BOA; …

  5. A B Radiation pressure acceleration (RPA) Macchi et al., PRL (2005,2009) • Circularly polarized or high-intensity LP lasers • No oscillating jxB, so electrons pile up as compressed layer • Ions are accelerated by the charge-separation, forming bunched layer. • Pressure balance Pes = Plaser: ion and electron layers accelerated together as quasi-neutral slab. • High beam density& efficiency; monoenergeticspectrum

  6. RPA scenarios l Leaky Light Sail Hole-Boring Light Sail

  7. Hole-boring (HB) regime: semi-infinite foil, d0 Acceleration via repeated reflections from HB surface ne compression region HB velocity ni Maximum proton velocity acquired depletion region ELx Robinson et al., PPCF (2009)

  8. Light-Sail (LS) RPA for micron-scale foil • Condition: • d0 ≈(/)(nc/n0) a0 > c/p • Electrons pile up at the foil rear side in a very thin layer, but are held insidebecause the laser field vanishes at its rear. • Leading edge of Ez bunches ions at the rear (d1<<d0) • Remaining ions are accelerated by the trailing edge of Ez, undergoing Coulomb explosion. • Later, the electron and ion layers combine together as a quasi-neutral plasma slab. compression region depletion region

  9. 1D PIC simulations seem to show that it is easy to get mono-energetic proton beam by CP lasers

  10. Rayleigh-Taylor –like instability!! BUT: stability of light-sail in multi-dimensional geometry problematic! decompression !! A. P. L. Robinson et al., New J. Phys. 10, 013021 (2008) B. Qiao et al., PRL 102, 145002 (2009). The slab loses electrons due to transverse instabilities, therefore becomes positively charged and debunches via Coulomb explosion F. Pegoraro et al., PRL 99, 065002 (2007)

  11. 100nc 30nc Unstable cases Stable LS RPA can be achieved by accelerating ions rapidly (> 1022W/cm2) B. Qiao et al., PRL 102, 145002 (2009).

  12. Can we get RPA to work at lower intensities? 1. By decreasing the foil thickness, an enhancement in both the peak energy and conversion efficiency of ion RPA can be achieved due to the limited mass. =nsls~n0l0 2. Efficient acceleration of protons are observed from nanometer diamond-like carbon (DLC)foil targets, which shows a great increase in proton energy. A. Andreev et al., PRL 101, 155002 (2009); A. Henig et al., PRL 103, 245003 (2009) 3. Progress in DLC atLMU (Habs et al.) thickness : 1nm~100nm, mass density: 2.7g/cm3, ratio C:H~10:1

  13. quasi-neutral region leakage region depletion region Leaky Light-Sail (LS) RPA for Nanofoils Condition: • The laser field does not completely decay within the foil (d0 < c/p) • => imperfect pressure balance • All foil electrons are accelerated and those near the rear side leak out into vacuum since the laser field does not vanish there. d0 ≈(/)(nc/n0) a0 < c/p

  14. 2D high-resolution PIC simulations with PIC code “ILLUMINATION” • Nanofoil target: density ne0=nip0=200nc (skin depth ls=11.3nm) thickness l0=8nm<ls • CP Laser pulse: intensity I0=3.41019 W/cm2(wavelength =1.0m) flattop with 40-cycle plateau and 1-cycle rise and fall times • Simulation box (15x12 m2) : 300003000 cells (0.54 nm); 800 particles/cell

  15. Proton nanofoil Plasma slab experiences RPA by the leading edge of Ez but leaks electrons from rear side Initial phase: Electrons pile up from front side and leak from rear side, forming three regions Coulomb explosion by the trailing edge of Ez

  16. Proton nanofoil Initial phase: Electrons pile up from front side and leak from rear side, forming three regions Coulomb explosion by the trailing edge of Ez Plasma slab experiences RPA by the leading edge of Ez but leaks electrons from rear side

  17. So why doesn’t it work? local netcharge Q • Leakage of electrons from the slab • => net positive charge locally • => Coulomb explosion by trailing edge of Ez. • Stable RPA needs accelerated proton layer to be surrounded by an excessof electrons • This keeps locally negative charge – hence leading edge Ez. leading edge (RPA) trailing edge (Coulomb explosion)

  18. LLS with multi-species target • A heavy ion with high charge state Z is accompanied with Z times more electrons than a proton for charge balance. • The accelerating proton layer may acquire charge-balancing electrons via the leakage from the heavy ion layer, so that it remains surrounded by an excess number of electrons • => avoid Coulomb explosion and preserve stable RPA ?

  19. Multi-species nanofoil Nanofoil target: electron density ne0=200nc, thickness l0=8nm<ls C6+ and H+ : nic0=32.65 nc, nip0=4.1nc with nic0:nip0=8:1 e- C6+ H+

  20. Proton layer poaches electrons from the C6+ layer, maintaining stable RPA • Separation of C6+ and proton layers – cf HB regime (Robinson, PPCF09) • The C6+ layer has insufficient charge-balancing electrons • => Coulomb explosion • Proton layer is surrounded by excess electrons • => Stable RPA

  21. Proton energy spectrum and time history typical for RPA A quasi-monoenergetic proton beam is obtained with density about 0.25nc,peak energy 18MeV, and particle number 108 Typical accelerating curves of RPA The conversion efficiency is 10%

  22. Scaling • Density ratio of C6+:H+can be changed from nic0:nip0=8:1 to 1:6 (above which cannot “borrow” any longer – optimum?) • The upper limit of the proton energy : • 100MeV proton beam can be obtained by CP laser at intensity 1020W/cm2 • B. Qiao et al., Phys. Rev. Lett., in press (October 2010) Up = 22L2/(2L+imic2)Ni L=I0SL laser pulse energy

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