Is a Plasma Diamagnetic?

Classical plasmas in thermodynamic equilibrium should be neither para- nor diamagnetic due to the action of the Lorentz force. Magnetic confinement, however, is based on the observed diamagnetism of laboratory plasmas. The apparent paradox is investigated on the basis of the resistive magneto-hydrodynamic equations. It is found that, at least in simple plasma configurations, these equations do not permit a solution, i. e. the paradox cannot be resolved. It seems that the Lorentz force is a test-particle approximation which is not suitable to describe the interaction of moving particles in agreement with the conservation of energy.