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Turbulence, reconnection and particle acceleration. W. H. Matthaeus, P. Dmitruk, N. Seenu Bartol Research Institute, University of Delaware M. R. Brown Swarthmore College SSX team members: C. Cothran. M. Landreman, D. Schlossburg.
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Turbulence, reconnection and particle acceleration W. H. Matthaeus, P. Dmitruk, N. Seenu Bartol Research Institute, University of Delaware M. R. Brown Swarthmore College SSX team members: C. Cothran. M. Landreman, D. Schlossburg 7th International Workshop on the Interrelationship between Plasma Experiments in Laboratory Space, Whitefish, Montana, June 29-July 3, 2003.
Test particles in 3D MHD turbulence • Test particle strategy (Ambrosiano et al, JGR 1988)
Acceleration of Charged Particles by Turbulence • Test particle approximation • Turbulent reconnection (2D) • Coherent and random contributions: • Coherent interaction with single reconnection site • Random v x b due to waves/nonlinearities • 2D turbulence • 3D turbulence Ambrosiano et al, JGR 1988 Gray and Matthaeus, PACP, 1992 Also see: Brown et al, ApJL, 2002 Lab. Exp. (SSX) Observation of Acceleration
2D MHD turbulence • Magnetic field lines as contours • Electric current density as gray shades • Random reconnection events • 512 x 512 resolution spectral method code
Test particle acceleration by turbulent reconnection Ambrosiano et al, Phys. Fluids, 1988 • 2D MHD reconnection • Not equilibrium • Broadband fluctuations • - fast reconnection Particle speed distribution High energy particles Particles are accelerated (direct and velocity diffusion) in region between X- and O-points. Powerlaw/exponential distributions.
Acceleration by 2D turbulence • In addition to acceleration by large scale 2D reconnection (with small scale turbulence), particles are accelerated in a very similar way by 2D homogeneous turbulence Test particles in 2D turbulence Gray and Matthaeus, PACP, 1992
Scaling of particle energy: • Scaling of energy depends upon testparticleA L/ (c/pi) Max energy Va B L 219 B2 L/n1/2 (ev) Goldstein et al. GRL, 1986 Note that: Energy containing scale/ ion inertial scale bandwidth of the inertial range
“V-B-L” scaling of charged particle energies SSX From K. Nakishima, Astron. Nachr, 1999
Reconnection in SSX M. Brown, PI C. Cothran M. Landremann
Reconnection in driven 3D RMHD turbulence • A nice example of a randomly occurring reconnection event in nearly standard geometry
Electric field in 3D MHD turbulence Electric field Magnetic field magnitude
Statistics of the induced electric field Milano et al, PRE, 2002 • For Gaussian v, b Induced E is exponential or exponential-like • Ind. E is localized but not as localized as the reconnection zones themselves. • Kurtosis 6 to 9 Dashed lines are theoretical Values for Gaussian v, b Spectral MHD simulation t = 3 30 years of 1 hour Solar Wind data
3D • 1283or 2563 pseudospectral method compressible MHD code (parallel implementation) • MPI load balanced test particle code • 50,000 particles with a= 100 to 100,000 and accuracy of 10-9 • Nonrelativistic particles intially at rest
Particle trajectories • 300 trajectories • Compare to locations of strong |E|
Acceleration of test particles by turbulent electric field a = tAlfven/tgyro • Particles start • with v=0 • Distribution after • 0.5 tAlfven • Two powerlaws
Scaling of particle energies Maximum energy Mean energy
Scaling of mean and maximum particle energy with alpha Energy ~ vBL or, a l E (alpha * E-correlation * typical electric field)
Conclusions • Charged test particles are accelerated by electric fields associated with turbulence and reconnection. • Phenomenon is very similar in • 2D turbulence • 3D turbulence • Reconnection in presence of small scale turbulence and large scale reconnection in the presence HD cascade produces transverse structure, associated with localized shear and reconnection sites. • V-B-L scaling seen in each case • SSX experimental results are consistent with the simulations. • Space and Astrophysical energy scalings are also consistent, including • Solar wind • Magnetosphere • Solar flares • Broad band test particle distributions are produced, with characteristic energies increasing with a= A