Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session MR0: Celebration of Plasma Physics Plenary Presentations III |
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Chair: Eugene Parker, University of Chicago Room: Landmark A/B |
Wednesday, November 19, 2008 8:00AM - 8:36AM |
MR0.00001: Waves in Space Plasmas Invited Speaker: Although low-frequency radio waves of extra-terrestrial origin were known over a century ago, it wasn't until the beginning of the space era fifty years ago that the origin of these waves could be adequately investigated. Since then spacecraft-borne instruments have shown that space plasmas exhibit an almost bewildering variety of wave phenomena, sometimes referred to as the plasma wave zoo. In this talk I will focus on two types of waves that occur in the magnetospheres of the strongly magnetized planets. They are whistler mode emissions and cyclotron maser radiation. Whistler mode emissions are generated in the now famous plasma wave mode known as the whistler mode, and cyclotron maser radiation is emitted mainly in the right-hand polarized free space mode. Both involve a cyclotron resonant interaction and require a perpendicular anisotropy to achieve wave growth. However, the origin of the anisotropy is different in the two cases. Whistler mode emissions occur in planetary radiation belts and are driven by the loss-cone anisotropy imposed by the planet. The resulting waves play a major role in the scattering and loss of radiation belt electrons. In contrast, the cyclotron maser radiation is generated in the auroral regions where parallel electric fields accelerate down-going electrons to high energies. The wave growth is driven by the shell distribution that arises from a combination of the parallel electric field and the magnetic mirror force. The resulting radiation is extremely intense and can be detected at great distances as an escaping radio emission. Both the whistler mode emissions and the cyclotron maser radiation display an amazing amount of fine structure. This structure is thought to be due to nonlinear trapping of the resonant electrons. The exact nonlinear mechanisms involved are still a topic of current study. [Preview Abstract] |
Wednesday, November 19, 2008 8:36AM - 9:12AM |
MR0.00002: Magnetic Islands in Plasmas Invited Speaker: Tearing modes are ubiquitous plasma instabilities whose final nonlinear stage involves the disruption of magnetic flux surfaces via the formation of magnetic islands. Over the years, a great deal of research has been performed on this subject within the magnetic fusion community, because an understanding of the dynamics of narrow magnetic islands is key to predicting under what circumstances such islands grow wide enough to adversely affect plasma confinement. The dynamics of magnetic islands which are sufficiently wide is well described by the celebrated single-fluid MHD theory of Rutherford. According to this theory, a magnetic island is essentially a three-dimensional plasma equilibrium which locally flattens the plasma pressure and grows on a resistive time-scale. Moreover, all of the free energy available to drive this growth comes from regions of the plasma well away from the island. On the other hand, the dynamics of a narrow magnetic island is influenced by a whole host of two fluid non-MHD effects. Some of these effects can prevent the complete flattening of the pressure profile across the island. Others lead to local sources of free energy which may greatly modify the island growth. This talk will describe the continuing efforts of plasma theorists to understand these effects, and hence to develop a fully comprehensive theory of magnetic island dynamics. [Preview Abstract] |
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