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Two fluid models of RF glow discharges, the non-equilibrium and equilibrium, are compared. The non-equilibrium fluid model is obtained by interpolating between a kinetic and a three-moment non-equilibrium formulation of the Boltzmann equation. The three-moment non-equilibrium model is valid in the time scale of the energy moment relaxation time and all coefficients are based on the mean energy. The equilibrium model is a single-moment model in which equilibrium conditions are assumed and the mean energy and average velocity relax to the equilibrium. Consequently, the transport coefficients in the equilibrium model are obtained from formulae based on local electric field and background gas pressure. Self-consistent RF glow discharge simulations for helium gas are carried out based on these two models, and the differences between the non-equilibrium and equilibrium models are compared. Owing to the finite relaxation time in the non-equilibrium model, momentum and energy, which require time and space to change in space-time varying electric fields, cannot change as rapidly as in the equilibrium model. Consequently, the non-equilibrium model shows the transition between the alpha and gamma regimes, a higher plasma density and a reduced sheath width.

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