Turbulence and particle confinement in a reversed-field pinch plasma

Abstract

The confinement properties of a reversed-field pinch (RFP) device are limited by the high level of magnetic stochasticity produced by the interaction of tearing modes in the plasma core. A way to reduce the core magnetic stochasticity is the application of the pulsed poloidal current drive (PPCD) technique. By applying the PPCD, tearing modes are stabilized, magnetic stochasticity and turbulence are reduced and hence the confinement is enhanced. In the TPE-RX device, standard RFP plasmas are characterized by magnetic and electrostatic edge turbulence dominated by intermittent phenomena; on the contrary, the improved confinement regime generated by the PPCD is characterized by turbulence with a self-similar nature. We show that the increase in τp is well correlated with the change in the nature of both the magnetic and the electrostatic turbulence. While plasmas with low confinement are dominated by intermittent events and by magnetic and electrostatic activity with a non-self-similar nature, plasmas with high confinement show turbulence with a self-similar character.