NG44A-01

The inverse cascade of magnetic helicity

* Müller, W Wolf.Mueller@ipp.mpg.de, Max-Planck-Institut für Plasmaphysik, Boltzmannstr.2, Garching, 85748, Germany
Malapaka, S slm@ipp.mpg.de, Max-Planck-Institut für Plasmaphysik, Boltzmannstr.2, Garching, 85748, Germany

The inverse cascade of magnetic helicity in three-dimensional magnetohydrodynamic turbulence is studied by means of high-resolution direct numerical simulations (DNS) of decaying and small-scale-driven turbulent flows. The observed self-similar inertial-range behavior of the magnetic helicity spectrum is significantly different from the results of earlier two-dimensional studies based on statistical closure models. The findings are explained by a model based on the statistical eddy-damped quasi-normal Markovian closure theory (EDQNM). It is shown that the inverse cascade of magnetic helicity is governed by the chirality of the turbulent velocity field.

NG44A-02

Self - Organization of Zonal Flows Driven by Drift Mode Turulence in Space and Astrophysical Plasmas

* Bingham, R r.bingham@rl.ac.uk, University of Strathclyde, 16 Richmond Street, Glasgow, G1 1XQ, United Kingdom
* Bingham, R r.bingham@rl.ac.uk, Science and Technology Facilities Council, Rutherford Appleton Laboratory Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom
Trines, R R.M.G.Trines@rl.ac.uk, Science and Technology Facilities Council, Rutherford Appleton Laboratory Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom
Mendonca, J T titomend@ist.utl.pt, lnstituto Superior Tecnico, Avenida Rovisco Pais, 1, Lisboa, 1049-001, Portugal
Silva, L O luis.silva@ist.utl.pt, lnstituto Superior Tecnico, Avenida Rovisco Pais, 1, Lisboa, 1049-001, Portugal
Shukla, P K ps@tp4.ruhr-uni-bochum.de, Institut fur Theoretische Physik IV, Ruhr Universitat Bochum, Bochum, D-44780, Germany
Dunlop, M W M.W.Dunlop@rl.ac.uk, Science and Technology Facilities Council, Rutherford Appleton Laboratory Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom
Vaivads, A Andris.Vaivads@irfu.se, Swedish Institute of Space Physics, Box 812, Kiruna, SE-981 28, Sweden
Davies, J A J.A.Davies@rl.ac.uk, Swedish Institute of Space Physics, Box 812, Kiruna, SE-981 28, Sweden
Davies, J A J.A.Davies@rl.ac.uk, Science and Technology Facilities Council, Rutherford Appleton Laboratory Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom
Bamford, R A r.a.bamford@rl.ac.uk, Science and Technology Facilities Council, Rutherford Appleton Laboratory Harwell Science and Innovation Campus, Didcot, OX11 0QX, United Kingdom
Mori, W mori@physics.ucla.edu, University of California, Los Angeles, 405 Hilgard Avenue., Los Angeles, 90095, United States
Tynan, G gtynan@ucsd.edu, Jacobs School of Engineering, University of California, 9500 Gilman Drive La Jolla,, San Diego, CA 92093-0, United States

The interaction between broadband drill mode turbulence and zonal flows is an important topic associated with transport at plasma boundaries. The generation of zonal flows by the modulational instability of broad band drift waves has resulted in the observation of self organized solitary wave structures at the magnetopause. To understand these structures and their importance in space and astrophysical plasmas we have developed a unique numerical simulation code that describes drift wave - zonal flow turbulence. We show that observations by cluster space craft confirms the role of drift wave zonal Mow turbulence at the Earth's magnetopause and further demonstrates that the magnetopause boundary acts in a similar manner to transport barriers in tokamak fusion devices. Applications to other plasmas will also be presented.

NG44A-03

Particle Diffusion in Chaotic Magnetic Fields Generated by Asymmetric Current Configurations

* Ram, A K abhay@mit.edu, Plasma Science and Fusion Center, Massachusetts Institute of Technolgoy, Room NW16-260, 167 Albany Street, Cambridge, MA 02139-4307, United States
Dasgupta, B dasgupta@ucr.edu, Institute of Geophysics and Planetary Physics, University of California at Riverside, 900 University Avenue, Riverside, CA 92521, United States

The observed cross-field diffusion of charged particles in cosmic rays is assumed to be due to the chaotic nature of the interplanetary/intergalactic magnetic fields. Among the classic works on this subject have been those of Parker [1] and Jokipii [2]. Parker considered the passage of cosmic ray particles and energetic solar particles in a large scale magnetic field containing small scale irregularities. In the context of cosmic ray propagation, Jokipii considered a small fluctuating component, added on to a uniform magnetic field, to study the spatial transport of particles. In these studies the irregular component of the magnetic field is prescribed in an ad hoc fashion. In contrast, we consider asymmetric, nonlinear, steady-state magnetic fields, in three spatial dimensions, generated by currents flowing in circular loops and straight lines [3]. These magnetic fields are completely deterministic and, for certain range of parameters, chaotic. We will present analytical and numerical studies on the spatial characteristics of these fields. The motion of charged particles in the nonlinear and chaotic magnetic fields is determined using the Lorentz equation. A particle moving in a deterministic chaotic magnetic field superposed on a uniform background magnetic field is found to undergo spatial transport. This shows that chaotic magnetic fields generated by simple current configurations can produce cross-field diffusion. A detailed analysis of particle motion and diffusion along with application to space plasmas will be presented. [1] E.N. Parker, Planet. Space Sci. 13, 9 (1965). [2] J.R. Jokipii, Astrophys. J. 146, 480 (1966), and J.R. Jokipii, Astrophys. J. 149, 405 (1967). [3] A.K. Ram and B. Dasgupta, Eos Trans. AGU 87 (52), Fall Meet. Suppl. Abstract NG31B-1593 (2006); and Eos Trans. AGU 88 (52), Fall Meet. Suppl. Abstract NG21B-0522 (2007).

Authors (2008), Title, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract xxxxx-xx