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 XR0: Celebration of Plasma Physics Plenary Presentations IV |
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Chair: Ian Hutchinson, Massachusetts Institute of Technology Room: Landmark A/B |
Friday, November 21, 2008 8:00AM - 8:36AM |
XR0.00001: Building on the Legacy of John Greene: The Transition to Chaos in Volume-Preserving Maps Invited Speaker: In 1968 John Greene began a thirty year odyssey that lead to a detailed understanding of, and precise computational tool for, the onset of chaos in two degree-of-freedom Hamiltonian systems and area-preserving maps. By all mathematical insight of the day, Greene's residue criterion---based on the stability of periodic orbits with rational winding numbers---should have dramatically failed to detect the breakdown of invariant tori. However, it not only worked, but also led to the discovery of self-similarity and renormalization for Hamiltonian dynamics. The residue criterion can be applied, for example, to toroidal magnetic configurations to accurately determine where tori exist and also to develop strategies for enlarging the volume with good surfaces. How much of Greene's vision can be applied to higher dimensional systems? While progress in the Hamiltonian case has been slow, in this talk I will discuss related phenomena for volume-preserving flows and maps. Again a natural application is to magnetic field configurations; however, magnetic nulls now preclude the use of two-dimensional cross sections. Mathematically, families of tori generically arise though a simple bifurcation that leads to the creation of a spheromak or Hill's vortex-like configuration. These tori can be subsequently destroyed by other bifurcations when there are resonances between the toroidal and poloidal winding numbers. Concepts similar to twist, or rotational transform, can be defined for these systems, and transport properties can be computed using a form of lobe dynamics. However, we do not know, as of yet, if there is a residue criterion. [Preview Abstract] |
Friday, November 21, 2008 8:36AM - 9:12AM |
XR0.00002: Perspectives on High-Energy-Density Physics Invited Speaker: Much of 21st century plasma physics will involve work to produce, understand, control, and exploit very non-traditional plasmas. High-energy density (HED) plasmas are often examples, variously involving strong Coulomb interactions and few particles per Debeye sphere, dominant radiation effects, strongly relativistic effects, or strongly quantum-mechanical behavior. Indeed, these and other modern plasma systems often fall outside the early standard theoretical definitions of ``plasma''. This presentation will focus on two types of HED plasmas that exhibit non-traditional behavior. Our first example will be the plasmas produced by extremely strong shock waves. Shock waves are present across the entire realm of plasma densities, often in space or astrophysical contexts. HED shock waves (at pressures $>$ 1 Mbar) enable studies in many areas, from equations of state to hydrodynamics to radiation hydrodynamics. We will specifically consider strongly radiative shocks, in which the radiative energy fluxes are comparable to the mechanical energy fluxes that drive the shocks. Modern HED facilities can produce such shocks, which are also present in dense, energetic, astrophysical systems such as supernovae. These shocks are also excellent targets for advanced simulations due to their range of spatial scales and complex radiation transport. Our second example will be relativistic plasmas. In general, these vary from plasmas containing relativistic particle beams, produced for some decades in the laboratory, to the relativistic thermal plasmas present for example in pulsar winds. Laboratory HED relativistic plasmas to date have been those produced by laser beams of irradiance $\sim $ 10$^{18}$ to 10$^{22}$ W/cm$^{2}$ or by accelerator-produced HED electron beams. These have applications ranging from generation of intense x-rays to production of proton beams for radiation therapy to acceleration of electrons. Here we will focus on electron acceleration, a spectacular recent success and a rare example in which simplicity emerges from the complexity present in the plasma state. [Preview Abstract] |
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