1. Physical Mechanism of the Transverse Instability in the Radiation Pressure Ion Acceleration Process Yang Wan Department of Engineering Physics, Tsinghua University Aug 2, 2016

2. Collaborators 2 THU – C. J. Zhang,, F. Li, Y. P. Wu, J. F. Hua, C.-H. Pai, W. Lu UCLA – X. L. Xu, C. Joshi, W. B. Mori GoLP – L. O. Silva CAEP – Y. Q. Gu

3. 3 Background of laser ion acceleration Physical analysis of transverse instability in the RPA process Physical picture Theoretical analysis Simulation and comparison Summary Outline

4. Laser ion acceleration 4 Juan C. Fernández. PPT @ LINAC08 Conference Victoria,British Columbia, Canada Sept. 29 –Oct. 3 (2008)

5. Laser ion acceleration 5 Heating Radiation pressure … Charge separation

6. Applications 6 Probing of strong electric fields in dense plasma on ps timescale Picosecond injectors for conventional accelerators Fast Ignition for ICF ~1um resolution 50μm Ta wire Imaging with 6-7MeV protons M. Borghesi, Phys. Plasmas (2002) Cowan, Phys. Rev. Lett. (2004) Cancer Therapy M. Roth et al., Phys. Rev. Lett. (2001) S. V. Bulanov et al., Phys. Lett. A (2002)

7. 7 Radiation Pressure Acceleration (RPA) Hole boring process (HB) (thick foil) A.Macchi, et al, Phys. Rev. Lett. 94, 165003 (2005). High contrast Circular polarization Radiation Pressure Acceleration

8. 8 the whole foil is accelerated Light Sail X. Zhang et al., Phys. Plasmas 14, 073101 (2007). X.Q. Yan et al., Phys. Rev. Lett. 100, 135003 (2008). A. P. L. Robinson et al., New J. Phys. 10, 013021 (2008). O. Klimo et al., Phys. Rev. ST Accel. Beams 11, 031301 (2008). A. Macchi et al, Phys. Rev. Lett. 103, 085003 (2009). Light sail process (LS) (ultrathin foil)

9. 2D/3D physical effects make RPA much challengeable Various mechanisms have been proposed to explain the transverse ripples Rayleigh-Taylor like instability; Weibel like instability; … Transverse instability related work 9 Electron heating Transverse instability

10. Related papers 10 All these models have not been able to give accurate predictions of mode structure and its growth rate in a large range of parameters

11. Physical picture 11 Sanmarti.Jr, Physics of Fluids 13, 1533 (1970). V. P. Silin, Soviet Physics Jetp-Ussr 21, 1127 (1965).

12. Analysis In the co-moving frame of high density layer only electrostatic fluctuations along the laser electric field will be considered. The cold, two fluid equations for ions and electrons Theoretical analysis 12

13. Theoretical analysis 13

14. Matrix Form equations Theoretical analysis 14

15. 15

16. 16 Parametervalue 800nm laser 0.2 pulse duration plane wave- density thickness Laser Proton densityFFT(Proton density) FFT Simulation and comparison: mode structure

17. Mode structure Simulation and comparison: mode structure 17 Good agreement

18. Growth rate 18 ++ + + - - - - new slice of fluid element moving in old slice of fluid element moving out High density layer

19. Growth rate Simulation and compare: growth rate 19 relatively good agreement

20. 20

21. Simulation and comparison: thick foil 21 Proton densityFFT(Proton density)

22. Simulation and comparison: thick foil 22 relatively good agreement

23. 23 Simulation and comparison: ultrathin foil

24. Two examples Simulation and comparison: ultrathin foil 24 Proton density FFT(Proton density)

25. Gaussian laser pulse test for different regimes Simulation: Gaussian profile test 25 Parametervalue 800nm laser 0.8 pulse duration density thickness Parametervalue 800nm laser 5 pulse duration density thickness

26. Transverse instability is a very vital problem in RPA process and also a fundamental physical problem in the laser solid interaction field. Fortunately, we have obtained a reasonable explanation to clarify the physical mechanism within it. It is shown that the density ripples are more likely induced by the coupling between the transverse oscillating electrons and quasi-static ions within this layer. The predictions of the mode structure and its growth rates have good agreements with the results obtained from the PIC simulations Brief summary 26 RegimeConditionMode structure (k) SA HB LS

27. 27 Thanks