Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session P4: Cross-fertilization Between Astrophysics and Laboratory Magnetized Plasma Physics |
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Sponsoring Units: DPP GPAP Chair: Vyacheslav Lukin, Naval Research Laboratory Room: Thurgood Marshall North |
Monday, February 15, 2010 10:45AM - 11:21AM |
P4.00001: Experimental/observational overview: what laboratory can offer to astro- and vice-versa Invited Speaker: There has been a recent synergy among laboratory experiments, astrophysical observations, and computation models. Important progress can be made if specific problems in plasma physics can be addressed by targeted experiments, careful astrophysical observations, and well-designed computer models. I will review some of the areas in which collaborative progress has been made (magnetic reconnection, astrophysical dynamos, turbulence) then focus on two specific problems. First, ion temperatures in the turbulent high corona and solar wind are known to scale with the ion mass ($T_i \propto M_i$). Laboratory measurements of ion temperature during reconnection-driven events in the MST reversed field pinch have a one scaling ($T_i \propto \sqrt{M_i}$) whereas impulsive events in the SSX reconnection device have another scaling ($T_i \propto Z/M_i$). Computer simulations are being planned to help sort out the discrepancies but evidently, different physics pertains in each system. Second, solar loops can now be imaged at sub-arcsecond resolution (scales $\le 700~km$ at the solar surface). The Hinode satellite has been used to resolve structure and dynamics of solar activity to the smallest scales. Both the Caltech Solar Coronal Loop Simulation Experiment and the Princeton Solar Flux Loop Experiment on MRX employ fast framing cameras to study rapid dynamics such as filamentation and footpoint motion. These magnetized loops formed in the laboratory can also be studied with internal probes to measure stability thresholds, Alfv\'en wave activity, and plasma relaxation. Connections among these laboratory experiments, space observations, and simulations will be emphasized. [Preview Abstract] |
Monday, February 15, 2010 11:21AM - 11:57AM |
P4.00002: Large scale dynamics of laboratory and astrophysical plasmas: bridging the lab/astro scale gaps and its limitations Invited Speaker: Large scale dynamics in a high temperature plasma tend to produce strong, large scale magnetic fields in the laboratory and astrophysical settings. It underlies two types of theory. The first is the conventional magnetic dynamo, which explains how plasma energy can be transformed into large scale magnetic energy. The second is the so-called magnetic self-organization, which explains how magnetic helicity introduced at a small scale source can be self-organized into system-scale magnetic fields. Examples of the first kind include the self-generated magnetic field in an inertially confined (ICF) plasma and the magnetic field in the accretion disk of stellar objects. The second kind includes the dramatic example of the megaparsec-scale radio lobe magnetic fields which are powered by the parsec-scale accretion disk of supermassive black holes, and the laboratory formation of spheromak and reversed field pinch by electrostatic helicity injection. Despite the huge scale separation between laboratory and astrophysical cases, the underlying physics appear to be surprisingly robust. Here I will first describe the theory of magnetic self-organization, and illustrate how a radio lobe can be formed and how it relates to the spheromak experiment. Specifically, the required extremely high efficiency in transferring gravitational infall energy into large scale radio lobe magnetic fields will be understood as the result of a resonant coupling between accretion disk and radio lobe plasmas, similar to a driven oscillator. The second part of the talk concerns a new form of kinetic magnetic dynamo, which is the result of anisotropic transport when hot plasmas meet a colder boundary. I will describe the underlying physical mechanisms and its laboratory and astrophysical implications. Since kinetic transport physics plays a decisive role in determining large scale dynamics, we are confounded with the interesting and difficult question of how to most effectively incorporate such physics in macro-modeling, especially in the case of nearly collisionless astrophysical plasmas. [Preview Abstract] |
Monday, February 15, 2010 11:57AM - 12:33PM |
P4.00003: Gyrokinetics in astrophysics -- from tokamaks to galaxies Invited Speaker: Gyrokinetic is a first principles theory for the dynamics and thermodynamics of magnetized, ionized gas. It has been developed over the last three decades, primarily in the magnetic confinement fusion community, where it is widely used to interpret observations and to design experimental devices and operational scenarios. Gyrokinetic simulations of instabilities and turbulence in hot, rarefied plasma have been tested carefully in these laboratory settings. Recently, gyrokinetic ideas and codes have been successfully used to explain long-standing and otherwise puzzling observations of turbulent fluctuations in the solar wind. While magnetohydrodynamics remains the appropriate theory for {\it dynamics} in larger, truly astrophysical plasmas (such as galaxy cluster plasmas), the appropriate framework for the study of many interesting thermodynamic processes in astrophysics (such as turbulent heating and transport) is gyrokinetics. Example applications will be shown. [Preview Abstract] |
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