Featured Researcher
UC Los Angeles: F. S. Tsung
Wave Particle Interactions in Magnetized Plasmas
Along with Dr. J. W. Tonge and Professor G. J. Morales of UCLA, we are currently using the DataStar computer at SDSC to investigate the interactions between low frequency electromagnetic waves and particles in magnetized plasmas. These interactions are important in a wide range of disciplines in plasma physics, including fusion plasmas, laboratory plasmas, and space plasmas. Computationally, this problem is complex because of the many timescales involved in the problem. On the one hand, the applied EM waves have frequencies which have the same timescales as the massive ions, and these waves are capable of accelerating electrons through wave-particle resonance. The large separation of scales, and the importance of keeping track of the detailed orbits of the particles make this problem a well suited for large parallel computers. Using DataStar, and our own cluster of Apple G5 servers called Dawson, we have been studying the interaction between particles and Alfvén waves in magnetized plasmas for the past four years and these simulations have led to the publication of several publications.[1,2]
Currently, we are using DataStar to investigate the conversion of perpendicular propagation (the so-called "Ordinary" and "Extraordinary" modes) to waves which propagate parallel to the applied magnetic field (Alfvén waves). This conversion is important in many areas of plasma physics. Specifically, we are motivated by the ongoing research in the Basic Plasma Science Facility (BAPSF). Our simulations suggest that this conversion occurs near the reflection point of the perpendicularly propagating waves, where the plasma density is modified by the reflection of the wave. The density modification in turn accelerate electrons along the field line near the reflection point, and these fast electrons are responsible for the generation of the Alfvén waves. These simulation observations agree well with experiments (see Fig (1)).
For more information, please visit the following web-sites:
References:
[1] F. S. Tsung, Phys. Rev. Lett 90, 055004 (2003).
[2] F. S. Tsung, J. Tonge, and G. J. Morales, Phys. Plas., 12, 012508 (2005).
Figure 1. The top left panels show the plasma device at BAPSF, located at UCLA. The top right panel shows the density the circular magnetic field (as arrows) form as a result of the density modification near the reflection layer (or the critical layer).
Figure 2: A movie of the density modification and magnetic field generation due to the interaction near the critical surface. The panel on the right is the ion density, and the left panel shows the excited magnetic field. The reflection layer is near 1/3 of the way from the left edge of the box. In this simulation, the wave modifies the density near the reflection layer and an Alfvén wave is excited from the reflection layer, moving parallel to the applied magnetic field (in the up/down direction in this movie).
