6. Wave in space plasma and Turbulence

1. 6. Wave in space plasma and Turbulence

2. Outline: • Background: wave in medium; • Electrostatic Wave in plasma; Langmuir wave ion-acoustic wave ion-cyclotron wave • Electromagnetic wave in plasma MHD wave Type III Radio burst • Turbulence; • Summary;

3. Wave

4. Wave in solid state physics • Phonon determine the property of the materials; conductor or semi-conductor Electron-hole pairs dominate the energy transportation

5. Why do we have wave problem in plasma? • Waves transfer energy in medium; • Waves dissipate the energy to cause heating; • Waves scatter the ions; • etc;

6. Waves • Plane wave assumption Phase and group velocities: Wave propagation Velocity of energy flow

7. Dispersion relation • Light in prism

8. Dispersion relation in solid state materials

9. Dispersion relation in space plasma

10. Earth whistler wave

11. Type III Solar radio burst (Electron burst)

12. Waves in the plasma • Electrostatic waves Langmuir waves or ion cyclotron waves • Electromagnetic waves light waves, MHD waves

13. Wave frequency range in plasma fluid • Ultra-low frequency Less than 1Hz • Extremely-low frequency 1Hz to 1kHz • Very-low frequency 1kHz to 10kHz

14. High frequency case Assume ions are stationary.

15. Two condition for an existing plasma waves • Must be a solution of appropriate equations; • Amplitude of wave is great than the background thermal fluctuations in the plasma.

16. Quiz 简要文字说明或者用数学表达式分别阐述波动中群速度和相速度。

17. + - - + - + - + - + Possible electron plasma oscillation

18. Langmuir oscillation One of the electrostatic waves The waves are generated by the electric charge separation, which is caused by thermal oscillation.

19. Irving Langmuir (31 January 1881 – 16 August 1957) He was awarded the 1932 Nobel Prize in Chemistry for his work in surface chemistry.

20. Langmuir oscillation (cont.) If only consider a separation of charges, we have plasma electron frequency

21. Langmuir wave • Adding electron thermal pressure Langmuir dispersion relation

22. Dispersion relation of Langmuir Wave

23. Ion-Acoustic waves • Now consider relative low frequency, while the ions’ contribution must be included.

24. Ion-Acoustic waves (cont.)

25. Ion-Acoustic waves (cont.) • Also adding electron thermal pressure contribution Dispersion of ion-Acoustic waves at small k limit

26. Dispersion relation of Ion-Acoustic waves

27. Cyclotron Frequency • 有磁场存在的等离子体

28. Cyclotron wave generated by pickup ions

29. Electrostatic waves • Only consider the oscillation dominated by the electric field which is caused by the separation of charges.

30. Electromagnetic waves • Also include the currents caused by charges oscillation.

31. Alfvén waves (MHD waves) • The waves is named after Dr. Hannes Olof Gösta Alfvén Alfvén wrote in a letter to the journal Nature in 1942: "If a conducting liquid is placed in a constant magnetic field, every motion of the liquid gives rise to an E.M.F. which produces electric currents. Owing to the magnetic field, these currents give mechanical forces which change the state of motion of the liquid. Thus a kind of combined electromagnetic-hydrodynamic wave is produced." Alfvén waves initiated the field of magnetohydrodynamics which subsequently earned Alfvén a Nobel Prize. Nobel Prize in Physics 1970

32. 色散关系在电离层电磁波反射上的应用 • Reflection of waves A cut-off occurred at the plasma frequency Also note:

33. Two-stream instability High speed cold electron stream moves fast relative to the ions, and plasma waves are generated;

35. Solar flare is the typical case of two-stream instability; • Solar radio burst (MHz) can be observed on ground.

36. Whistler mode • Why we see a whistler?

37. High phase and group velocities correspond high frequency, vica verse.

38. Solar radio emission • In addition to the strong thermal radiation of the quiet Sun there is intense radio emission from bursts that are associated with phenomena of solar activity likeflares and coronal mass ejections (CMEs). Radio bursts cause “snow storm” on CCD

39. Solar radio bursts • Type I (Short, narrow band events that usually occur in great numbers together with a broader band continuum.) • Type II (shock front burst) • Type III (electron burst) • Type IV (Flare-related broad-band continua) • Type V (Langmuir burst)

40. Type II radio burst

41. Coronal shock

42. Type III solar radio burst • These bursts are generated when suprathermal electrons (velocity ~ 0.05 to 0.3 c, where c is the speed of light) are ejected from solar active regions and then travel outward along open magnetic field lines through the corona and interplanetary medium.

43. Scenario of Type III burst and Type U burst

46. Green Bank Solar Radio Burst Spectrometer The Green Bank Solar Radio Burst Spectrometer (GBSRBS) provides dynamic spectra of solar radio bursts during daylight hours in the western hemisphere.

47. Solar Radio Bursts Could Cripple GPS • 空间天气预报的重点之一 All satellites broadcast at the same two frequencies, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal).

48. Importance of solar radio observations • Observations of the flare related processes can help to improve the understanding of solar activity. Today, many of them are far from understood. • Monitoring the solar activity can help to minimize damage of strong CMEs on technical equipment on Earth. A better understanding of the observations can eventually lead to predictions of the effects on Earth and allow for fast provision.

49. One application: electromagnetic waves can be used to measure density of ionoshpere

50. Wave particle interaction • How do ions response the waves? Resonant absorption or resonant amplification