Alfvénic turbulence associated with density and temperature filaments

Abstract

A systematic laboratory study of controlled density and temperature filaments having transverse scale length comparable to the electron skin-depth has been performed in the large plasma device (LAPD) at UCLA. It is found that large amplitude shear Alfvén waves develop spontaneously and are localized within the filaments. As the plasma conditions change (e.g., lowering the plasma beta parameter or increasing the heating power) the highly coherent eigenmodes develop into broad band Alfvénic turbulence. A kinetic description that includes the effect of coulomb collisions has been developed to understand the linear properties of the modes. Excellent agreement with the measured eigenfunctions is found for the density filaments in the higher beta regime in which the modes remain strongly coherent. The similarity between the broad band fluctuation spectra generated in a variety of plasma configurations suggest the possibility of a universal process involving filamentary structures and spontaneously generated Alfvénic turbulence.