Evidence of a Subkinetic Spectral Break in a Strongly Turbulent Collisionless Plasma
Journal Article
Overview
abstract
Abstract; ; 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; ; ; ≈; 1; ; ; . In the subion range, which spans from the ion inertial length (; d; ; ι; ; ) 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 (; ρ; ; 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; ; ; ≈; 1; ; ; . We also confirm that at; ; ; ; ; ; ; ; ; k; ; ; ; ; ; ρ; ; ; e; ; ; >; ~; 2; ,; ; ; ; the energy density of; ; B; ; and; ; E; ; approaches equipartition, suggesting that energy transfer is near complete.;
