Inhibition of electron thermal conduction by electromagnetic instabilities

Heat flux inhibition by electromagnetic instabilities in a hot magnetized plasma is investigated. Low-frequency electromagnetic waves become unstable due to anisotropy of the electron distribution function. The chaotic magnetic field thus generated scatters the electrons with an effective mean free path λ^eff. Saturation of the instability due to wave-wave interaction, nonlinear scattering, wave propagation, and collisional damping is considered. The effective mean free path is found self-consistently, using a simple model to estimate saturation level and scattering, and is shown to decrease with the temperature gradient length, L. The results, limited to the assumptions of the model, are applied to astrophysical systems. For interstellar clouds with β ≫ 1 and whose sizes are well below 10²¹ cm, the instability is found to be important, keeping the value of ε = λ_eff/L near 10^-3. For dense plasma such as laser-produced plasma it is argued that collisional damping stabilizes the plasma even if ε is of order unity and in this case the heat conduction may be dominated by superthermal electrons. Several as yet unresolved issues are discussed.