Laser trigged proton acceleration from ultrathin foil

Transcription

1 Laser trigged proton acceleration from ultrathin foil A.V. Brantov 1, V. Yu. Bychenkov 1, D. V. Romanov 2, A. Maksimchuk 3 1 P. N. Lebedev Physics Institute RAS, Moscow , Russia 2 All-Russia Research Institute of Automatics, Moscow , Russia 3 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA

2 Applications of ion beams new high-time resolution diagnostic techniques, since the short ion pulse duration; ion beam radiography / imaging and lithography; applications in energy research (ion Fast Ignitor in the inertial fusion energy context); medical treatment (proton therapy, transmutation of short lived radio-isotopes for positron emission tomography (PET) in hospitals); short neutron source. astrophysical phenomena in the Lab

3 Experiments on proton acceleration from ultrathin foils by ultra-short laser pulses ASTRA-Gemini (~2 J) I = W/cm 2, τ = 50 fs, λ= 800 nm, focused in 3 μm(fwhm) HERCULES laser (~1 J) I = W/cm 2, τ = 30 fs, λ= 800 nm, focused in 1.2 μm (FWHM) Target Al, 35 R. Prasad et. al APL11, NIMA11 Target CH, Si 3 N 4 S.A. Reeds et. al. IFSA 2011 Best shot 20 MeV 20Mev/J record!

4 PIC code for simulation of laser-plasma interaction Kinetic equation particle method Maxwell equation differential mesh schema 3D relativistic parallel particle-in-sell code interaction of powerful ( W/cm 2 ) ultra-short laser pulses with plasma. Restriction - ionization and particle collision do not take into account - computational power

5 PIC code Mandor for simulation of laser-plasma interaction 3D3V relativistic electromagnetic massively parallel particle-incell code Key technologies are developed and tested in Novosibirsk during last 25 years Last 8 years it was intensively used in LPI to solve practical problems: Weibel and electromagnetic instabilities, laser particle acceleration Code is regularly benchmarked against similar foreign codes (PICLS code by Sentoku, etc) and shows comparable result Runs on Russia largest supercomputer Lomonosov (18 th in Top500) 1373 Tflops, CPU

6 Mandor advantages - sophisticated domain decomposition - massively parallel Example of domain decomposition in Mandor -quiet start (without any noise) -arbitrary shape of target (example of target created by Mandor) - varies initial distribution function of plasma particle - realization of tightly focusing laser pulse - varies diagnostics and visualization

7 PIC code for simulation of laser-plasma interaction Laser pulse 2 ρ target z 2 τ L x y Target electrons ions x y z = 20 λ 16 λ 16 λ Δx Δy Δz = λ/100 λ/20 λ/20 - different target forms (foil, disk, spherical clusters ) - pre-plasma modeling with linear or exponential densities profiles

8 Optimal target thickness 2D simulations ( p - polarization) 2D simulations ( s - polarization) 3D simulations I = W/cm 2 (a 0 =12.8), τ = 45 fs, focused in 4 μm (FWHM) 8 Target CH foil with n e =200 n c 2D simulation overestimates times proton energy. 2D simulation results are different for s- and p- polarization

9 3D simulation of laser pulse interaction with thin foil of optimal thickness Proton density Proton spectrum I = W/cm 2 (a 0 =12.8), τ = 45 fs, focused in 4 μm (FWHM) Most energetic protons Target CH foil with n e =200 n c

10 Optimal target thickness for tightly focused laser pulse I = W/cm 2 focused in 2 μm (FWHM) (f # = 1.3) I = W/cm 2 focused in 1 μm (FWHM) (f # = 0.55) E max = 64 MeV E max = 67 MeV

11 Proton acceleration for HERCULES parameters I = W/cm 2 (a 0 =30), τ = 30 fsec, focused in 1.2 μm (FWHM) Target CH foil (50% Н, n e =210 n c ) Expanded foil with linear density gradient l 0

12 Targets with pre-plasma I = W/cm 2 (a 0 =30), τ = 30 fsec, focused in 1.2 μm (FWHM) t=25 t=50 t=75 t=100 t=125 fsec Front side pre-plasma results in some increase of proton energy

13 Ion acceleration from thin foil Target shape Density profile Proton spectra Front-side expansion small pre-plasma

14 Ion acceleration from thin foil modified by pre-pulse Target shape Density profile Proton spectra Front-side expansion large pre-plasma (artificial model case) Two-side symmetrical expansion

15 Angular distribution of energetic protons Plain foil Both side expansion Angle, Plain foil Angle, ɛ, MeV Front-side expansion Spectra of protons propagating in the cone with Angle, the opening angle of 1 o ɛ, MeV Both side expansion ɛ, MeV

16 Comparison with experimental data Plain foil Experimental proton spectrum obtained with Thomson Parabola ion spectrometer (TP). The solid angle covered by the TP is 10 7 in the target normal direction.

17 Optimal target thickness of thin foil irradiated by powerful laser pulse I = W/cm 2 focused in 4 μm (FWHM), 15 fsec I = W/cm 2 focused in 2 μm (FWHM) (f # = 1.3), 30 fsec 2D simulations ( p - polarization) 3D simulations 2D simulations ( s - polarization) E max = 220 MeV E max = 254 MeV

18 Optimal condition to maximize proton energy T. Esirkepov et al., Phys. Rev. Lett. 96, (2006) Plasma transparency condition Is proton energy ε proportional a (square root from laser intensity)?

19 Conclusion Based on 3D simulation with code MANDOR it has been shown that utilization ultra-thin foils and high-contrast laser beams may results in generation of proton beams with thermal spectrum and maximum energy of the order of 50 MeV for 2J laser energy and more than 200 MeV if energy on the target exceeds 20 J. The comparison of 3D results vs. 2D results has been presented. 2D simulation overestimate maximum proton energy in times. Sharp laser focusing in a focal spot with a size of the order of 2 wavelength seems have advantage in terms of generation of protons beam with maximum energy for given laser energy. The proper pre-plasma density profile can help to reproduced experimental data. Thank you to all of you for listening