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Shanghai Institute of Optics and Fine Mechanics (SIOM) , Shanghai

西湖国际聚变理论与模拟研讨会 M. Y. Yu 郁明阳 Institute for Fusion Theory and Simulation Zhejiang University Hangzhou 2008.12.26. with W. Yu, H.B. Zhuo, X. Wang, L.H. Cao, H. Xu, B.F. Shen, Z.M. Sheng, J. Zhang, etc. Shanghai Institute of Optics and Fine Mechanics (SIOM) , Shanghai

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Shanghai Institute of Optics and Fine Mechanics (SIOM) , Shanghai

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  1. 西湖国际聚变理论与模拟研讨会M. Y. Yu 郁明阳Institute for Fusion Theory and SimulationZhejiang UniversityHangzhou 2008.12.26

  2. with W. Yu, H.B. Zhuo, X. Wang, L.H. Cao,H. Xu, B.F. Shen, Z.M. Sheng,J. Zhang,etc. Shanghai Institute of Optics and Fine Mechanics (SIOM), Shanghai National University of Defense Technology (NUDT), Changsha Institute for Applied Physics and Computational Mathematics (IAPCM), Beijing Jiaotong University, Shanghai

  3. Trapping and focusing of laser light by small solid cavity targets and ion acceleration

  4. Main point Hollow sphere and cone of similar size as the short laser pulse

  5. Light pulse becomes a “nonlinear cavity mode”? Boundary modified by the light pulse Trapped light is still coherent! Need definition and analytical theory!

  6. Short-pulse laser interaction with matter • Electrons strongly driven by EM wave field • Ionization of target by pulse front • Strong light pressure on plasma electrons • Almost all affected electrons driven away • Strong space-charge field formed • Ions are driven by the space-charge field or Coulomb explode • In 2D and 3D: everything also in the transverse direction

  7. Ponderomotive force Space dependent Particles are always pushed to the lower-field region

  8. Ponderomotive force of light Taylor expand PF is independent of the sign of the charge, and dependent on the gradient of the field energy

  9. Nonlinear light-matter interaction initiated by the ponderomotive force(light-pressure force)on the electrons Relativistic: Same form as the kinetic or hydrodynamic pressure force

  10. short pulse  large force

  11. Trapping of laser light in small spherical cavityapplied toion acceleration

  12. Laser pulse and cavity are of similar dimension Solid density target Cavity Laser pulse

  13. Laser-light trapping by mircrocavity ion density electromagnetic energy density Cavity is of similar size as laser pulse 70% light energy enters cavity, the rest is reflected Light pulse remains coherent (becomes cavity mode?)

  14. Physical process 1. Laser pulse enters the cavity 2. Pulse edge ionizes the cavity surface 3. Light pressure drives out plasma electrons in surface 4. Resulting space-charge field accelerates, compresses, and heats the ions in a surface layer 5. Compressed plasma expands into the cavity 6. High-pressure ion region forms at center

  15. electrons ions EM energy

  16. In the plane z =10 ni Ey Pi Ti

  17. At cavity center Ion temperature ni Ti

  18. Ashley, et al. Fusion Technology Institute University of Wisconsin Similar to ion focusing ininertial electrostatic confinement (IEC) Anode 40-50 cm 100V ac @ 245kHz Cathode10cm - 25 to - 60 kV A neutron Source

  19. Not the same as hohlraum EM waves inside is not coherent 1 mm Our micron sized cavity is much smaller than

  20. Focusing of laser light by small hollow coneapplied toion acceleration

  21. Short laser pulse and hollow cone 2m w = 10 m D =15m a0= 4 D = 1m n=10nc  = 25T

  22. EM energy density in 30 deg cone Laser light becomes a thin high-intensity needle-like spot before defocusing

  23. Nonlinear laser-plasma interacton Electron density

  24. Radial profile of EM energy density, as the peak of light pulse passes the left and right openings The light is focused into a tiny spot of 1m radius, with large intensity enhancement!

  25. Can greatly improve the pulse contrast!

  26. Percentage of reflected and transmitted light energy Optimum-intensity regime

  27. No focusing!

  28. Ray tracing with cone wall acting like mirror Poor transmission and no focusing

  29. Ion acceleration using cone focused light

  30. Put a foil target in front of the open cone tip 2m, 10nc foil

  31. EM energy density ion density Mono-energetic ion bunch a0 = 4

  32. Ion energy density (only the highest- density parts are shown)

  33. Explains why a cone guide leads to better emission (electron heating) 2.45-MeV thermal neutrons R. Kodama et al., Nucl. Fusion 44, 276 (2004)

  34. 謝謝！

  35. Intense (>1020 watt/cm2)short-pulse (10-15 s)laser interaction with matter Short pulse (chirped) Ultra short-pulse (~ 1 fs) pulse

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