New concept of light ion acceleration from low-density target A.V. Brantov, V. Yu. Bychenkov September 27, 2017

Applications of ion beams new high-time resolution diagnostic techniques, since the short ion pulse duration [Borghesi PoP2002]; ion beam radiography / imaging and lithography; applications in energy research (ion “Fast Ignitor” in the inertial fusion energy context) [Roth PRL2001, Bychenkov Sov. Plasma Phys. 2001, Guskov QE2001]; medical treatment (proton therapy [Bulanov Sov. Plasma Phys. 2002], transmutation of short lived radio-isotopes for positron emission tomography (PET) in hospitals [Fritzler APL2003]); short neutron source [Roth PRL2013]; astrophysical phenomena in the Lab; nuclear physics [Bychenkov JETP99].

Recent experiments on proton acceleration F. Wagner et.al PRL 116, 205002 (2016) I. J. Kim et.al PoP 23, 070701 (2016) Laser: ~160-200J; 500-800 fs; I ~ (0.7-2.6)×1020 W/cm2 Laser: ~1 PW; 27J; 30 fs; 8.5 J on target, 6.1×1020 W/cm2 Polymethylpentene foil, thickness165-1400 nm, gold foil, 4 μm Polymer foil, thickness of 15 nm, (2.5° from normal) Proton energy 85 МэВ Proton energy 93 МэВ

Optimal target thickness Proton energy from foil target Proton energy from double-layered target 2D PIC simulation 150 TW 300 TW 500 TW ne =100 nc ne =400 nc There is optimal thickness for given density and laser intensity ! Condition of plasma transparency Coulomb field Laser field Absorption ? Ion energy ?

Problem of laser light transmission through plasma layer L.D. Landau & E.M. Lifshitz Electrodynamics of Continuous Media reflection transmission A=1- R –T absorption T R A

PIC code for simulation of laser-plasma interaction Laser pulse 2 ρ z target 2  0.3 - 300 J, 5×1019 -5×1022 W/cm2 2 τ = 30 fs 2 ρ = 4 μm Linear/circular polarization y x l ~ 0.01 - 10 λ Target CH2 foil (ne=200 nc ) electrons heavy ions light ions (protons) x  y  z = 50   20   20  x   y   z = /100  /20  /20

3D proton acceleration by 30 J laser pulse I =5 1021 W/cm2 ,  = 30 fs, focus spot 4 m (FWHM) Target – CH2 foil 0.1 m (ne=200 nc )

Proton acceleration from ultra-thin foils Phys. Rev. ST Acc. Beams 18, 021301(2015) t = 30 fs, ρ = 2 μm t = 30 fs, ρ = 4 μm t = 30 fs, ρ = 6 μm t = 150 fs, ρ = 4 μm Laser:  = 30-150 fs, 2-6 m (FWHM) I = 5×1018 W/cm2 --5×1022 W/cm2 Target: CH2 foil (ne=200 nc ) with optimal thickness l = 0.005λ - λ

Thin foils: linear vs. circular polarization linear polarization

Thin foils: linear vs. circular polarization ponderomotive field only ponderomotive field TNSA field 30 J, 5×1021 W/cm2 target thickness 0.13 λ/0.8 λ 2 τ = 30 fs 2 ρ = 4 μm linear/circular polarization

Thin foils: linear vs. circular polarization I stage of acceleration - ponderomotive acceleration laser light reflected from target Circular polarization – 85 MeV Linear polarization – 60 MeV I III II III stage of acceleration – like TNSA Circular polarization – from 240 to 290 MeV Linear polarization – from 150 to 230 MeV II stage of acceleration – most effective laser moves together with protons Circular polarization – from 85 to 240 MeV Linear polarization – from 60 to 150 MeV Semi-transparent target – possibility to increase interaction time !

Thin foils: linear vs. circular polarization 30 J, 5×1021 W/cm2 2 τ = 30 fs 2 ρ = 4 μm linear/circular polarization 109 protons with energy > 200 MeV 1.3 times maximum energy increase 2.5×109 protons with energy > 200 MeV

Proton acceleration: maximum energy vs Proton acceleration: maximum energy vs. thickness & density of the target. 30 J New regime of acceleration – increasing acceleration time ! Laser: = 30 fs, 4 m (FWHM) I = 5×1021 W/cm2 Target: CH2 plastic& aerogel

Proton acceleration: maximum energy vs Proton acceleration: maximum energy vs. thickness & density of the target. Laser: = 30 fs, 4 m (FWHM) I = 1022 W/cm2 60 J 12 J Target: CH2 plastic& aerogel Laser: = 30 fs, 4 m (FWHM) I = 2×1021 W/cm2

Experiment to increase acceleration time S. Kar et. al Nat. Comm. 7, 10792 (2016) Laser: ~3 J, 30 fs; I~ 1020 W/cm2 Simulation 30J, 30 fs

Synchronization of ion and field velocities vg Laser pulse E σ xe Relativistic ponderomotive force MeV V. Yu. Bychenkov et al, JETP Letters104, 618 (2016)

Proton acceleration by ponderomotive potential Ponderomotive force pushed electrons Acceleration of captured protons Laser laser 1 PW 30 J 30 fс 5×1021 W/cm2 Accelerated field A. Brantov, et al Phys. Rev. Lett. 116, 085004 (2016) Innovative targets ( ρ~1÷20 mg/cm3 )

3D PIC simulation of SASL

SASL regime: linear vs. circular polarization linear polarization

SASL regime for circularly polarized laser pulse Ex

SASL regime: linear vs. circular polarization 30 J, 5×1021 W/cm2 2 τ = 30 fs 2 ρ = 4 μm linear/circular polarization 5×109 protons with energy > 200 MeV 1.6 times maximum energy increase 1.3×1010 protons with energy > 200 MeV Plasma Phys. Control. Fusion 59, 034009 (2017)

Thin foil vs. SASL regime: circular polarization Protons from low-density targets in SASL regime Protons from thin foils of optimal thickness

Innovative low-density targets for particle acceleration Thickness – 100- 200 nm SWNTs with density of 0.1 mg/cm3 SWNTs with density of 1 mg/cm3 - To enrich the films with hydrogen the nanotubes have been filled with coronene (C24H12) molecules. - 2 mass % of hydrogen can be introduced into films. SWNTs with density of 30-50 mg/cm3 Thickness – 5- 10 μm Phys.Rev. Acc. Beams 20, 061301 (2017)

Conclusion Thank you for attention New dependence of maximum proton energy from laser intensity is demonstrated. Circularly polarized laser pulse has advantage in terms of ion acceleration from thin foils and low-density targets. The new mechanism of ion acceleration from low-density targets by slow light is proposed. Thank you for attention