MAGNETIC FLUCTUATION DRIVEN CROSS-FIELD PARTICLE-TRANSPORT IN THE REVERSED-FIELD PINCH

Electrostatic and electromagnetic fluctuations generally cause cross-f ield particle transport in confined plasmas. Thus core localized turbu lence must be kept at low levels for sufficient energy confinement in magnetic fusion plasmas. Reversed-field pinch (RFP) equilibria can, th eoretically, be completely stable to ideal and resistive (tearing) mag netohydrodynamic (MHD) modes at zero beta. Unstable resistive intercha nge modes are, however, always present at experimentally relevant valu es of the poloidal beta beta(theta). An analytical quasilinear, ambipo lar diffusion model is here used to model associated particle transpor t. The results indicate that core density fluctuations should not exce ed a level of about 1% for plasmas of fusion interest. Parameters of e xperimentally relevant stationary states of the RFP were adjusted to m inimize growth rates, using a fully resistive linearized MHD stability code. Density gradient effects are included through employing a parab olic density profile. The scaling of particle diffusion [D(r)proportio nal to lambda(2)n(0.5)T/aB, where lambda is the mode width] is such th at the effects of particle transport are milder in present day RFP exp eriments than in future reactor-relevant plasmas. (C) 1997 American In stitute of Physics.