1. Enhancement of electron injection using two auxiliary interfering-pulses in LWFA Yan Yin ( 银燕 ) Department of Physics National University of Defense Technology

2. Outline Laser Wakefield Accelerator (LWFA) Trapping, Acceleration & Injection of Electrons Enhancement of Electron Injection by Using two Auxiliary Interfering-Pulses in LWFA Stage 1: Moving Electron Density Grating Formation in the Beating Field of Auxiliary Pulses Stage 2: The Interfering-pulses Auxiliary LWFA (IPA-LWFA) scheme

3. LWFA: Background & Progress E. Esarey, C. B. Schroeder, and W. P. Leemans, Rev.Mod.Phys., 81,001229(2009) PBWA:

4. S. P. D. Mangles et al., NATURE, 431, 535, 2004. C. G. R. Geddes et al., NATURE, 431, 538, 2004. J. Faure, Y. Glinec, A. Pukhov et al., NATURE, 431, 541, 2004. J. Faure, C. Rechatin, A. Norlin et al., NATURE, 444, 737, 2006. W. P. Leemans, B. Nagler, A. J. Gonsalves et.al., Nature Phys., 2. 418, 2006. I. Blumenfeld, C. E. Clayton, F. J. Decker et.al., Nature, 445,741, 2007. N. A. M. Hafz, T.M. Jeong, I. W. Choi et.al., Nature Photonics, 2, 571, 2008. H.-P. Schlenvoigt, K. Haupt, A. Debus et.al., 4, 130, 2008. S. F. Martins, R. A. Fonseca, W. Lu et al., NATURE Phys., 6, 311, 2010. List but a few…..

5. Trapping & Acceleration of Electrons Rayleigh diffraction Pump depletion, instability, … Dephasing length: E. Esarey and M. Pilloff, Phys. Plasmas, 2, 1432 (1995)

6. Effects limiting acceleration Dephasing length Rayleigh diffraction Pump depletion, beam loading, instability, … Electron boosted Wake slow down How does the election enter the acceleration phase of wakefield?

7. Injection of Electrons Self-injection Optical injection  Ponderomotive injection  Cold optical injection Ionization injection Injection by density transition

8. Self-injection in bubble regime S. Kalmykov et.al., Phys. Rev. Lett., 103, 135004 (2009) V.Malka et.al., Nature Phys. 4,447(2008)

9. Ponderomotive injection by colliding pulses D. Umstadter, J. K. Kim, and E. Dodd, Phys. Rev. Lett., 76, 2073(1996) E. Esarey et. al., Phys. Rev. Lett., 79, 2682(1997) H. Kotaki et.al., Phys. Plasmas, 11, 3296(2004)

10. J. Faure, C. Rechatin, A. Norlin et al., Nature, 444, 737, 2006.

11. H.Kotaki et.al., Phys. Rev. Lett., PRL 103, 194803 (2009)

12. Cold optical injection by using circularly polarized colliding pulses X. Davoine et.al., Phys. Rev. Lett., 102, 065001(2009)

13. Enhanced self-injection of electrons by using two auxiliary interfering-pulses in LWFA Auxiliary laser intensity: nonrelativistic ~10 16 W/cm 2

14. Stage 1 Moving Electron Density Grating Formation in the Beating Field of Auxiliary Pulses

15. From the set of two-stream fluid equations, the electron density modulation equation is obtained [1] : [1] Z. M. Sheng, J. Zhang and D. Umstadter, Appl. Phys. B 77, 673 (2003).

16. Standing field Quasi-charge-neutrality Small velocity modulation Z. M. Sheng, J. Zhang and D. Umstadter, Plasma density gratings induced by intersecting laser pulses in underdense plasmas. Appl. Phys. B 77, 673 (2003).

17. Beating field Especially, when Spatial period: Moving velocity:

18. 1D PIC simulation: 0 50 150 200

19. theoretical prediction simulation results 0.57λ 0 t=140T 0 theoretical prediction simulation results 0.113c 0.09c

20. Large velocity modulation of electrons Pre-accelerated electrons are more easily trapped in the wakefield excited by the pump laser

21. Stage 2 The Interfering-pulses Auxiliary LWFA (IPA-LWFA) scheme

22. 1D PIC simulation: 0 50 150 200 Perpendicularly- polarized

23. It is the initial status of plasmas when the short intense pump laser is incident.

24. IPA-LWFALWFA

25. 2D PIC simulation

29. Summary Efficient injection schemes are desired for electron acceleration Moving electron density gratings can be generated by two low-intensity interfering pulses Enhanced self-injection of electrons is obtained in the IPA-LWFA scheme.