Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session JM10: Mini-Conference: The Magnetic Universe -- A Mini-Conference in Honor of Stirling Colgate III |
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Chair: Mark Nornberg, University of Wisconsin-Madison Room: Salon FGH |
Tuesday, October 28, 2014 2:00PM - 2:30PM |
JM10.00001: Extragalactic Jets as Electrical Circuits and Transmission Lines Philipp Kronberg I describe the first attempt to measure a current in an extended radio galaxy jet: $\sim$ 10$^{18}$A at $\sim$ 50 kpc from the elliptical galaxy's ultra-compact nucleus. This class of jet is known to transport its magnetic energy ``intact'', up to supragalactic scales. I discuss plasma parameters for 3C303 and recent attempts to measure its jet axial current. I discuss analogies with both electrical circuits, -- and transmission lines. Power is delivered into a ``load'', whose impedance, $Z$, is close to that of free space, and the jet power flow $I^{2}Z$ is $\sim$ 10$^{35}$ erg s$^{-1}$ -- broadly consistent with astronomically measured total power outputs, luminosities and lifetimes of AGN-powered radio lobes.The current and power levels are also consistent with SMBH accretion disk model predictions by Stirling Colgate, H. Li, V. Pariev, J. Finn, and others, beginning with Lovelace 1976 (Nature). A further analogy with transmission lines shows how the supragalactic power flows can be disrupted by a complex impedance in the ``circuit.'' Reactive components in space, i.e. a complex $Z$, can disrupt, reflect or deflect the power flow. This could explain the wide variety of magneto-plasma configurations seen in these systems. [Preview Abstract] |
Tuesday, October 28, 2014 2:30PM - 2:50PM |
JM10.00002: Lab experiments investigating astrophysical jet physics Paul Bellan Dynamics relevant to astrophysical plasmas is being investigated in lab experiments having similar physics and topology, but much smaller time and space scales. High speed movies and numerical simulations both show that highly collimated MHD-driven plasma flows are a critical feature; these collimated flows can be considered to be a lab version of an astrophysical jet. Having both axial and azimuthal magnetic fields, the jet is effectively an axially lengthening plasma-confining flux tube with embedded helical magnetic field (flux rope). The jet velocity is in good agreement with an MHD acceleration model. Axial stagnation of the jet compresses embedded azimuthal magnetic flux and so results in jet self-collimation. Jets kink when they breach the Kruskal-Shafranov stability limit. The lateral acceleration of a sufficiently strong kink can provide an effective gravity which provides the environment for a spontaneously-developing, fine-scale, extremely fast Rayleigh-Taylor instability that erodes the current channel to be smaller than the ion skin depth. This cascade from the ideal MHD scale of the kink to the non-MHD ion skin depth scale can result in a fast magnetic reconnection whereby the jet breaks off from its source electrode. [Preview Abstract] |
Tuesday, October 28, 2014 2:50PM - 3:10PM |
JM10.00003: Inward radial transport in differentially rotated plasma discs formed in z-pinch experiments Sergey Lebedev, M. Bennett, G.F. Swadling, L. Suttle, E. Blackman, G. Burdiak, J.P. Chittenden, A. Ciardi, R.P. Drake, A. Frank, G.N. Hall, J. Hare, S. Patankar, R.A. Smith, F. Suzuki-Vidal We will present experimental results showing the development of instabilities and an inward transport of matter in a differentially rotating supersonic plasma disc with dimensionless parameters relevant to modeling physics of astrophysical discs. The converging off-axis plasma flow forming the disc is produced by ablation of wires in a cylindrical wire array z-pinch (1.4MA, 250ns) combined with a cusp magnetic field, and the rotating disc is supported in equilibrium by the ram pressure of the flow. The radial profile of rotation velocity in the disc is measured using Doppler shifts of the ion feature of Thomson scattering spectra, while the broadening of the spectra yields the plasma temperature. The evolution of the disc structure is observed with multi-frame XUV and optical cameras, and the plasma density is measured using end-on laser interferometry. The Reynolds number in the disc is sufficiently large (\textgreater 10$^{\mathrm{5}})$ to allow development of turbulence on the time-scale of the experiment, and the observed inward transport of matter with the growth of small scale structures suggests that turbulence is responsible for the transport. [Preview Abstract] |
Tuesday, October 28, 2014 3:10PM - 3:40PM |
JM10.00004: Rossby Wave Instability in Astrophysical Disks Richard Lovelace, Hui Li A brief review is given of the Rossby wave instability in astrophysical disks. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disk surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (proportional to Exp[im$\phi$ ], m = 1,2,...) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in protoplanetary disks. The Rossby vortices in the disks around stars and black holes may cause the observed quasi-periodic modulations of the disk's thermal emission. Stirling Colgate's long standing interest in all types of vortices - particularly tornados - had an important part in stimulating the research on the Rossby wave instability. [Preview Abstract] |
Tuesday, October 28, 2014 3:40PM - 4:00PM |
JM10.00005: Challenges of Astrophysical Disk-Jet-Lobe Systems Hui Li Supermassive black holes residing at the centers of most massive galaxies are widely regarded as (the) sources of the non-thermal energy in the universe. Much of the black hole formation energy is released through an accretion disk around the (spinning) black hole and the powerful jets/lobes emanating from it. The fate of these jets and lobes could have important implications in terms of the overall magnetization of the wider inter-galactic medium. Many unsolved problems remain in trying to understand the physics of these systems and the need for more plasma physics is acute. We discuss how astronomical observations, laboratory experiments, theory and simulations are helping us to make progress. [Preview Abstract] |
Tuesday, October 28, 2014 4:00PM - 4:20PM |
JM10.00006: Accretion Disks and Cosmic Rays Ken Fowler We model accretion disks as Faraday disks with current and mass flows perpendicular to 2D mean field flux surfaces. We model jets produced by accretion disks as weakly-unstable current flows. We model cosmic ray acceleration arising from jet kink modes producing a runaway ion beam that finally accelerates itself by cyclotron resonance. All of these processes can be unified by an Ohm's Law in which Spitzer resistivity is replaced by a generalized hyper-resisitivity, ultimately yielding several predictions in rough agreement with observations. [Preview Abstract] |
Tuesday, October 28, 2014 4:20PM - 4:40PM |
JM10.00007: High Energy Plasmas Associated with Black Holes at ``Near'' and ``Far'' Distances* Bruno Coppi The radiation emission from Shining Black Holes is most frequently observed to have non-thermal features. Therefore, relevant collective processes in plasmas surrounding or emanating from black holes and containing high-energy particles with non-thermal distributions in momentum space are considered. The case where significant temperature anisotropies are present is analyzed. In plasmas close to black holes[1] these anisotropies are shown[2] to have a critical influence on: a) the existence and characteristics of stationary plasma and field configurations; b) the excitation of magneto-gravitational modes driven by temperature anisotropies and differential rotation; c) the generation of magnetic fields over macroscopic scale distances; d) the outward transport of angular momentum. The $\gamma$-ray ``bubbles'' emerging from the disk of Our Galaxy are connected to a stream of high energy protons emerging from the central massive black hole and to the excitation of plasma modes associated with the non-thermal features of the proton distributions and providing energy to the radiation emitting electron populations. *Sponsored in part by the U.S. DOE.\\[4pt] [1] B. Coppi, \textit{A\&A}. 548, A84 (2012).\\[0pt] [2] B. Coppi, MIT-LNS HEP Report 13/01 (2013), submitted \textit{Ap. J.} (2014). [Preview Abstract] |
Tuesday, October 28, 2014 4:40PM - 5:00PM |
JM10.00008: Energetics of the magnetic reconnection in laboratory and space plasmas Masaaki Yamada The essential feature of magnetic reconnection is that it energizes plasma particles by converting magnetic energy to particle energy. This talk addresses this key unresolved question; how is magnetic energy converted to plasma kinetic energy during reconnection? Our recent study on MRX [1] demonstrates that more than half of the incoming magnetic energy is converted to particle energy at a remarkably fast speed ($\sim$ 0.2$V_{A})$ in the reconnection layer. A question arises as to whether the present results should be applied to magnetic reconnection phenomena in the space astrophysical plasmas. In a reconnection region of effectively similar size in the Earth's magnetotail, the energy partition was carefully measured during multiple passages of the Cluster satellites [2]. The half length of the tail reconnection layer (L) was estimated to be 2000--4000 km namely 3--6 $d_{i}$, (ion skin depth); the scale length of this measurement is very similar to the MRX case, $L$ $\sim$ 3$d_{i}$. Reconnection in the magneto-tail is driven by an external force, i.e., the solar wind, and the boundary conditions are very similar to the MRX setup. The observed energy partition is notably similar, namely, more than 50{\%} of the magnetic energy flux is converted to the particle energy flux, which is dominated by the ion enthalpy flux, with smaller contributions from the electron enthalpy and heat flux. A broad implication will be discussed.\\[4pt] [1] M. Yamada et al, This conference, Submitted \textit{to Nature Communications} (2014).\\[0pt] [2] J. P. Eastwood \textit{et al.}, \textit{PRL }\textbf{110}, 225001 (2013). [Preview Abstract] |
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