Abstract

On the basis of a variational formulation of the Vlasov-Maxwell theory it was recently shown that, for instance, all magnetically confined plasmas allow the existence of negative energy waves. Such waves can become nonlinearly and dissipatively unstable and might therefore be of importance in explaining anomalous transport. The proof of this result uses infinitely strongly localized perturba tions. This is, however, not necessary: in this paper it is shown by discussing general, homogeneous, magnetized plasmas that the necessary localization is related to the average gyroradius rg of the relevant particle species. For unstable plasmas the extent or wavelengths of negative energy waves can be of the order of rg, whereas for linearly stable plasmas the extent can be a small fraction of rg.