Towards 100 MeV proton generation using ultrathin targets irradiated with petawatt laser pulses

Transcription

1 IZEST_Tokyo Towards 100 MeV proton generation using ultrathin targets irradiated with petawatt laser pulses Chang Hee Nam 1,2, I J. Kim 1,3, H. T. Kim 1,3, I. W. Choi 1,3, K. H. Pae 1,3, C. M. Kim 1,3, S. K. Lee 1,3, J. H. Sung 1,3, and T. M. Jeong 1,3 1 Center for Relativistic Laser Science, Institute for Basic Science (IBS), Korea 2 Dept of Physics and Photon Science, Gwangju Inst. of S&T, Gwangju, Korea 3 Advanced Photonics Research Institute, GIST, Gwangju, Korea

2 Overview I. Experimental scheme of Proton/ion acceleration - Acceleration mechanism - Experimental scheme II. Experimental results - Linear polarization - Circular polarization - 3D PIC simulation III. PW laser upgrade

3 Mechanism of proton/ion acceleration Target normal sheath acceleration Radiation pressure acceleration Proton acceleration by the electrostatic field Balance between the charge separation and the ponderomotive force Acceleration mechanism laser Target thickness Characteristics Energy scaling TNSA I>10 18 W/cm 2 linear pol. ~ μm Broad spectrum Thermal electrons RPA I>10 20 W/cm 2 linear pol. circular pol. ~ 10 nm Quasi-monoenergetic, collective electrons

4 Target Chambers for PW Laser Experiments Target Chamber II Plasma mirror Target Chamber I Compressor II Compressor I

5 PW Plasma mirror: contrast enhancement Plasma formation on double plasma mirrors Temporal profiles measured with a third-order cross-correlator. Contrast 10-8 (w/o PM) -> (w/ PM) Contrast enhancement: 10 4

6 PW Target chamber for proton experiment Target: polymer (F8BT) Thickness: nm Intensity range w/ PM: 0.5x10 20 W/cm 2 6x10 20 W/cm 2 Polarization on target: s-pol or circular Incidence angle: deg. to normal OAP f = 60-80cm Target surface monitor CR39 Target Focal spot monitor Proton beam To Thomson Parabola

7 I. Experimental scheme of Proton/ion acceleration II. Experimental results - Linear polarization - Circular polarization - 3D PIC simulation III. Conclusion

8 Proton and C 6+ measured with Thomson parabola Energy spectra of protons and carbon ions obtained from a 10-nm-thick polymer target irradiated with I = W/cm 2. Highest proton energy: 45 MeV

9 Proton and C 6+ Generation using PW Pulses Intensity scaling from ~ I 1/2 to ~ I Proton Transition from TNSA to RPA C 6+ ion E p ~ I E p ~ I 1/ W/cm 2 (linear polarization) W/cm 2 (linear polarization)

10 Energy spectra of protons and C 6+ ions Laser intensity: 3.3x10 20 W/cm 2 Proton spectrum Exponential decay (100 nm) vs. plateau structure (10 nm) C 6+ spectrum Quasi-monoenergetic peaks (10 nm)!

11 Electron energy spectra for polymer targets I=3.3x10 20 W/cm 2 TNSA Thermal electrons RPA Collective electrons Two-component electrons are generated from 10 nm target!

12 Temporal evolution of electron & proton densities 3D PIC simulation 10-nm polymer; I=3.0 x W/cm 2 Electron Proton

13 Proton distribution in phase space Protons accelerated by RPA are faster than those accelerated by TNSA RPA TNSA x10 W/cm, 10 nm Z( m) 1.5 RPA 0.15 TNSA x10 W/cm, 10 nm Z( m) fs 0.25 RPA TNSA Z( m) 24 fs TNSA N (arb. units) Pz(/mc) 0.15 RPA x10 W/cm, 30 nm Z( m) fs TNSA Pz(/mc) W/cm2 30-nm target, 1.0 x RPA Z( m) fs 0.20 TNSA 0.10 RPA TNSA x10 W/cm, 30 nm RPA 2 3x10 W/cm, 10 nm Z( m) Maximum proton energy is determined by TNSA fs x10 W/cm, 10 nm Protons accelerated by RPA are slower than those accelerated by TNSA N (arb. units) Pz(/mc) fs N (arb. units) 24 fs N (arb. units) W/cm2 10-nm target, 3.0 x N (arb. units) 0.25 Maximum proton energy is determined by RPA x10 W/cm, 30 nm Z( m) fs TNSA RPA x10 W/cm, 30 nm Z( m)

14 Radiation Pressure Acceleration: Light Sail laser pulse electrons Protons/ ions Coulomb force

15 Temporal evolution of maximum proton energy 10-nm target; 3.0 x W/cm 2

16 Vertical position ( m) Focusing with F/3 Optics Focal spot size : 4.1 mm (FWHM) Horizontal position ( m) Energy concentration > 25% in the FWHM area Radius ( m) Laser on target: 8.5 J, 30 fs Focal spot size obtained with F/3 OAP: 4 m Energy concentration in the FWHM area: > 25% W/cm 2 for 1 PW laser + DPM

17 Proton and C 6+ spectra measured with Thomson parabola Circularly polarized, 30fs, 4.1 μm FWHM, 5.7x10 20 W/cm 2, 15 nm polymer 80 MeV (H + ) 50 MeV (H + ) 150 MeV (C 6+ ) 30 MeV (H + ) 90 MeV (C 6+ ) 20 MeV (H + ) 60 MeV (C 6+ ) 10 MeV (H + ) 30 MeV (C 6+ ) C 6+ H + Zero order Logarithmic scale Generation of 80 MeV protons!

18 Actual scaling for proton energy?

19 PW Ti:Sapphire Laser

20 Upgrade: High Contrast, 20 fs, 4 PW Laser

21 High Contrast, 20 fs, 4 PW Ti:sapphire Laser 5.2 PW Spectrum bandwidth: 84 nm Output energy: 86 J Pulse width: 16 fs Peak Power: 4 PW / 77%

22 Summary 1. Proton acceleration from ultrathin polymer targets with 30 fs, PW laser pulses has been performed, obtaining the max proton energy of 58 Mev and 80 Mev when driven by linearly and circularly polarized laser pulses, respectively. 2. The scaling of max proton energy indicates that the RPA mechanism overtakes the TNSA, especially in the max proton energy for the case of nm targets. 3. The laser upgrade to 4 PW is going on for further proton acceleration.