Large scale magnetic fields and coherent structures in nonuniform unmagnetized plasma

Abstract

The properties of streamers and zonal magnetic structures in magnetic electron drift mode turbulence are investigated. The stability of such large scale structures is investigated in the kinetic and the hydrodynamic regime, for which an instability criterion similar to the Lighthill criterion for modulational instability is found. Furthermore, these large scale flows can undergo further nonlinear evolution after initial linear growth, which can lead to the formation of long-lived coherent structures consisting of self-bound wave packets between the surfaces of two different flow velocities with an expected modification of the anomalous electron transport properties.

On the modulational stability of magnetic structures in electron drift turbulence

“…It is also noted that the resulting criterion is very similar to the one previously found in Ref. 23 for the case of a monochromatic wave spectrum. However, because of its more general nature, it shows that the monochromatic case underestimates the increment by a factor of 4 and it also yields a higherorder correction to this increment.…”

“…The latter result is exactly the same as was found for the case of a monochromatic wave spectrum in Ref. 23. In fact, if we compare the increments directly with the corresponding definitions of the coefficients used, we find that in the limit k Ӷ1, the increment of the modulational instability is four times as high as the one for the hydrodynamic regime.…”

“…[17][18][19][20][21][22] Furthermore, two regimes of large-scale magnetic field generation have recently been investigated in Ref. 23 and yielded a general criterion concerning the local form of the wave spectrum in the case of the kinetic regime ͑where resonance was assumed͒ and an explicit result for the hydrodynamic regime, where a monochromatic wave spectrum allowed the integration over all modes. Also, a sufficient criterion for large-scale structure generation was found in the form of Nyquist's criterion in Ref.…”

On the kinetic stability of magnetic structures in electron drift turbulence

“…Another reason for this example is its similarity with the case of a monochromatic distribution, which was investigated earlier in Ref. 13.…”

“…Two regimes of large-scale magnetic field generation have recently been investigated in Ref. 13 and yielded a general criterion concerning the local form of the wave spectrum in the case of the kinetic regime ͑where resonance was assumed͒ and an explicit result for the hydrodynamic regime, where a monochromatic wave spectrum allowed the integration over all modes. In this paper, the goal is to find an instability criterion using a wave kinetic equation similar to the case of kinetic wave theory, where we have the so-called Nyquist criterion.…”