Evidence of a Subkinetic Spectral Break in a Strongly Turbulent Collisionless Plasma
Year: 2026
Type: article
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.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
OpenAlex ID: W7154231899