A possible route to spontaneous reduction of the heat conductivity by a temperature gradient driven instability in electron-ion plasmas

We have shown that there exist low-frequency growing modes driven by a global temperature gradient in electron and ion plasmas by linear perturbation analysis within the framework of plasma kinetic theory. The driving force of the instability is the local deviation of the distribution function from the Maxwell-Boltzmann distribution due to a global temperature gradient. Application of the results to the intracluster medium is being reduced to 5-7 orders of magnitude less than the mean free paths due to Coulomb collisions. This may provide a hint in explaining why hot and cool gas can coexist in the intracluster medium in spite of the very short evaporation timescale due to thermal conduction if the conductivity is the classical Spitzer value. Our results suggest that the realization of the global thermal equilibrium is postponed by the local instability, which is induced for a quicker realization of the local thermal equilibrium state in plasmas. The instability provides a new possibility to create and grow cosmic magnetic fields without any seed magnetic field.