(Color online) Potential field for F b in the simulation plane. The amplitudes were assigned in the wavenumber space, with a flat modal spectrum and random phases, enforcing ∇ · F b = 0 exactly. This forcing excites magnetic fluctuations in the plane of the simulation.
(Color online) (a) Magnetic energy versus time for several forcing frequencies ωd . The two vertical lines denote the time period over which the total energy change is plotted in (b) Omnidirectional spectra for the same runs. −5/3 line and the ion inertial length scale kdi = 1 have been shown for reference purposes.
Time averaged magnetic and thermal energies in the time window t ∼ 40 to t ∼ 50 as a function of driving frequency. Near the critical frequency of 0.4, points are labeled with the corresponding values of the driving frequency in NL time units based on individual runs. The critical frequency corresponds to (vertical arrow). For frequencies higher than the critical frequency, the scaling of magnetic energy can be shown to be −2 power law which we get for forcing in the absence of a plasma. (We wish to thank the referee for this observation.) The fall off of the thermal energy follows a much steeper −5 power law in this regime. The and power laws are shown as dashed lines.
(Color) k − ω spectrum of the out-of-plane magnetic field Bz fluctuations for (a) ωd = 0.0 and (b) ωd = 13.4. Physical scales and cyclotron frequency denoted with solid white lines. Magnetosonic mode denoted with dashed white line. In (b), the first few Bernstein modes calculated from a linear Vlasov code24 shown as solid curves. (c) PDFs of magnetic field vector increments for various driving frequencies and vector increments of δs = 10Δx.
Article metrics loading...
Full text loading...