Satellites reveal hidden physics in plasma turbulence near Earth

<p>We investigate the magnetic (B) and electric (E) field spectra in the dissipation range of strong turbulence of a collisionless plasma. This investigation, which is relevant to turbulence studies in many astrophysical settings, is enabled by high-resolution measurements from the four-spacecraft Magnetospheric Multiscale (MMS) mission in the Earth's magnetotail. B and E spectra are derived as a function of the product of the wave number and electron skin depth (|k|d(e)) using a novel technique that employs time-delay analysis on multiple intervals of B and E. Using the MMS tetrahedral formation with close (several d(e)) spacing, velocities of B and E signals can be derived so that native frequency-based spectra can be accurately translated to k spectra. The most important finding is a mathematically significant break in the B spectral index that appears at |k|d(e )approximate to 1. In the subion range, which spans from the ion inertial length (d(iota)) to d(e), the B spectral index is -2.35, then steepens to -3.13 at sub-d(e) scales. As expected from previously derived frequency spectra, E has a particularly shallow spectral index (-0.67) in the subion range. At scales smaller than d(e) and/or the electron thermal gyroradius (rho(e)), the E spectral index steepens to -2.73. Spectral breaks in both B and E in the dissipation range indicate a change in the physical dissipation processes from ion to electron domination at |k|d(e )approximate to 1 .We also confirm that at |k|rho(e )&gt; -2 the energy density of B and E approaches equipartition, suggesting that energy transfer is near complete.</p>