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

2. 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].

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

4. 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 ?

5. 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

6. PIC code for simulation of laser-plasma interaction
Laser pulse
2 ρ z
target
2  J,
5× ×1022 W/cm2
2 τ = 30 fs
2 ρ = 4 μm
Linear/circular polarization y x
l ~ 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

7. 3D proton acceleration by 30 J laser pulse
I = W/cm2 ,  = 30 fs, focus spot 4 m (FWHM)
Target – CH2 foil 0.1 m (ne=200 nc )

8. Proton acceleration from ultra-thin foils
Phys. Rev. ST Acc. Beams
18, (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:  = 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

9. Thin foils: linear vs. circular polarization
linear polarization

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

11. 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 !

12. 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

13. 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

14. 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

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

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

17. 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, (2016)
Innovative targets ( ρ~1÷20 mg/cm3 )

18. 3D PIC simulation of SASL

19. SASL regime: linear vs. circular polarization
linear polarization

20. SASL regime for circularly polarized laser pulseEx

21. 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, (2017)

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

23. Innovative low-density targets for particle acceleration
Thickness – 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 mg/cm3
Thickness – μm
Phys.Rev. Acc. Beams 20, (2017)

24. 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