Density limits and scaling laws in reversed field pinchs

High and low density limits observed in RFP are discussed. An optimum density is found which scales with the plasma current amplitude. These observations, along with the fact that in RFP experiments #betta#sub(THETA)approx.=0.1 is obtained fairly independently on the plasma current, are consistent with a linear temperature-current dependence and a classical energy confinement time scaling. A comparison with tokamak and, in particular, with the behaviour of #betta#sub(THETA) evidences that tokamak scalings do not apply to RFP experiments. However in larger higher current devices, similar temperatures and energy confinement times could be obtained in RFP's and ohmically heated tokamaks. (orig.)