Helical small-scale turbulent motions lead to an enhancement of magnetic energy. First the small-scale field grows then the field of the largest scale. Due to the conservation of magnetic helicity the large-scale field grows only on resistive time scales.
left: volume rendering of the z-component of the magnetic field
right: loglog plot of the power spectrum for the magnetic energy
Simulations in a 128**3 triply periodic box with a helical forcing, which is random in time. The non-relativistic MHD equaitons for an isothermal gas are solved with the PencilCode.
Download in higher resolution: bz_128_kf_15_a.mpg
[ arxiv:1208.4529 ]
2D hydrodynamics simulation of a Kolmogorov flow with high Reynolds number. A small initial disturbance in the velocity field gets increased by the instability. The colors represent vorticity.
Simulation done in a 512*512*1 box for resistive hydrodynamics with the PencileCode.
Download in higher resolution: kolmogorov_highRe.mpg
2D hydrodynamics simulation of a Kolmogorov flow with low Reynolds number. A small initial disturbance in the velocity field gets increased by the instability. The colors represent vorticity.
Simulation done in a 256*128*1 box for resistive hydrodynamics with the PencileCode.
Download in higher resolution: kolmogorov_lowRe.mpg
Magnetic field lines in a simulation with the Borromean rings as initial magnetic field configuration. The colors represent the magnitude of the field. At the end of the simulations two separated helical structures appear. Their magnetic helicity is of opposite sign. Simulation done in a 256*256*256 box for resistive MHD with the PencileCode.
Download in higher resolution: borromean_fieldlines.mpg
[ Phys. Rev. E, 84(1):016406, 2011 ]
Magnetic field lines in a simulation with a IUCCA knot as initial magnetic field configuration. The colors represent the magnitude of the field. At the end of the simulations two separated helical structures appear. Their magnetic helicity is of opposite sign. Simulation done in a 256*256*256 box for resistive MHD with the PencileCode.
Download in higher resolution: iucaa_256a.mpg
[ Phys. Rev. E, 84(1):016406, 2011 ]
Magnetic field lines in a simulation with a 4-foil knot as initial magnetic field configuration. The colors represent the magnitude of the field. The topology of the system is preserved in form of internal twist. Simulation done in a 128*128*128 box for resistive MHD with the PencileCode.
Download in higher resolution: video_fieldlines_4foil.mpg
[ Phys. Rev. E, 84(1):016406, 2011 ]
Magnetic field lines in a simulation with a trefoil knot as initial magnetic field configuration. The colors represent the magnitude of the field. The topology of the system is preserved in form of internal twist. Simulation done in a 128*128*128 box for resistive MHD with the PencileCode.
Download in higher resolution: trefoil_128a1_fluxtubes.mpg
[ Phys. Rev. E, 84(1):016406, 2011 ]
Volume rendering of the magnetic energy for a simulation with a trefoil knot as initial magnetic field configuration. Simulation done in a 128*128*128 box for resistive MHD with the PencileCode.
Download in higher resolution: trefoil_128a1_vdf.mpg
[ Phys. Rev. E, 84(1):016406, 2011 ]
Magnetic field lines in a simulation with three interlocked flux rings and zero magnetic helicity. The colors represent the magnitude of the field. The topology of the system gets apparently destroyed. Simulation done in a 256*256*256 box for resistive MHD with the PencileCode.
Download in higher resolution: H0_256d2.mpg
[ Phys. Rev. E, 81:036401, 2010 ]
Magnetic field lines in a simulation with three interlocked flux rings and finite magnetic helicity. The colors represent the magnitude of the field. The topology of the system is conserved. Note the twist of the inner ring as the outer rings reconnect. This reflects helicity conservation. Simulation done in a 256*256*256 box for resistive MHD with the PencileCode.
Download in higher resolution: H4_256d2.mpg
[ Phys. Rev. E, 81:036401, 2010 ]
