1. Electron acceleration by Langmuir turbulence Peter H. Yoon U. Maryland, College Park

2. Outline Laboratory Beam-Plasma Experiments Beam-plasma instability & Langmuir turbulence Solar wind electrons Conclusions

3. LABORATORY BEAM-PLASMA EXPERIMENTS Part 1.

4. Alexeff et al., Hot-electron plasma by beam- plasma interaction, PRL, 10, 273 (1963). 5 keV DC electron beam interacting with plasma yields 250 keV X ray photons.

5. Tarumov et al., Investigation of a hydrogen plasma with “hot” electrons, Sov. Phys. JETP, 25, 31 (1967).

6. During the discharge phase the hot electron component was 1/10, which increased to 1/3 in the decay phase.

7. Levitskii and Shashurin, Spatial development of plasma-beam instability, Sov. Phys. JETP, 25, 227 (1967).

9. Whelan and Stenzel, Electromagnetic radiation and nonlinear energy flow in an electron beam-plasma system, Phys. Fluids, 28, 958 (1985).

11. Outline Laboratory Beam-Plasma Experiments Beam-plasma instability & Langmuir turbulence Solar wind electrons Conclusions

12. BEAM-PLASMA INSTABILITY AND LANGMUIR TURBULENCE Part 2.

13. Bump-in-tail instability Langmuir Turbulence generated by beam-plasma interaction

14. Langmuir oscillation Ion-sound wave

15. t x E(x,t)E(x,t)

16. t x E(x,t)E(x,t) Langmuir wave

18. 1D approxiation Ions (protons) are taken as a quasi-steady state, and the electrons are made of two components, one background Gaussian distribution, and a tenuous beam component.

19. Backgroun d (thermal) electrons Beam electrons

22. T Umeda, private communications

24. Bump-in-tail instability

25. Beam-plasma or bump-in-tail instability

26. Bump-on-tail instability A.A. Vedenov, E. P. Velikhov, R. Z. Sagdeev, Nucl. Fusion 1, 82 (1961). W. E. Drummond and D. Pines, Nucl. Fusion Suppl. 3, 1049 (1962).

28. Bump-in-tail instability

29. Weak turbulence theory L. M. Gorbunov, V. V. Pustovalov, and V. P. Silin, Sov. Phys. JETP 20, 967 (1965) L. M. Al’tshul’ and V. I. Karpman, Sov Phys. JETP 20, 1043 (1965) L. M. Kovrizhnykh, Sov. Phys. JETP 21, 744 (1965) B. B. Kadomtsev, Plasma Turbulence (Academic Press, 1965) V. N. Tsytovich, Sov. Phys. USPEKHI 9, 805 (1967) V. N. Tsytovich, Nonlinear Effects in Plasma (Plenum Press, 1970) V. N. Tsytovich, Theory of Turbulent Plasma (Consultants Bureau, 1977) A. G. Sitenko, Fluctuations and Non-Linear Wave Interactions in Plasmas (Pergamon, 1982)

30. Backscattered L wave

33. ~ g = 1/(n D 3 ) Discrete-particle (collisional) effect

34. Weak turbulence theory

37. P. H. Yoon, T. Rhee, and C.-M. Ryu, Self-consistent generation of superthermal electrons by beam-plasma interaction, PRL 95, 215003 (2005). Long-time behavior of bump-on-tail Langmuir instability

38. Outline Laboratory Beam-Plasma Experiments Beam-plasma instability & Langmuir turbulence Solar wind electrons Conclusions

39. SOLAR WIND ELECTRONS Part 3.

43. STEREO spacecraft

45. WIND spacecraft

46. 2007 January 9 Linghua Wang, Robert P. Lin, Chadi Salem

47. By Linghua Wang, Davin Larsen, Robert Lin fe(v)fe(v) Electron Velocity Distribution

48. Outline Laboratory Beam-Plasma Experiments Beam-plasma instability & Langmuir turbulence Solar wind electrons Conclusions

49. CONCLUSIONS Part 4.

50. Beam-plasma interaction is a fundamental problem in plasma physics. Laboratory experiment shows electrons accelerated by beam-plasma interaction. Electron beam-excited Langmuir turbulence theory adequately explains the laboratory results and predict the formation of energetic tail distribution. Solar wind electrons feature energetic tail population confirming Langmuir turbulence acceleration theory.