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Abstract: We show that in a neutral magnetized plasma there exist microscopicoscillatory modes, with wavelengths of the order of magnitude of the meaninterparticle distance, which become unstable when the electron density exceedsa limit proportional to the square of the magnetic field. The model we consideris just a linearization of the classical one for neutral plasmas, namely asystem of electrons subjected to Coulomb interactions among themselves and witha uniform positive neutralizing background. This model is here dealt with as anactual many-body problem, without introducing any averaging over the individualparticles. The expression of the density limit coincides, apart possibly from anumerical factor of order one, with the well-known Brillouin density limit fora nonneutral plasma, which has however a macroscopic origin. The density limithere found has the same order of magnitude as the operational density limitobserved in several conventional tokamak devices. We finally show that, whenthe full electromagnetic interactions are taken into account, dispersionrelations are obtained which for short wavelengths reduce to those obtainedhere in the purely Coulomb case, and for long wavelengths reproduce thefamiliar ones of MHD.

Author: M. Marino, M. Zuin, A. Carati, E. Martines, L. Galgani

Source: https://arxiv.org/


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