Modeling of Anomalous Transport in ECRH Plasmas at HSX

The Weiland ITG/TEM anomalous transport model [1] is used to predict density and temperature profiles in ECRH plasmas at HSX. The local geometry approximation in [1] is replaced by the local geometry in the low-field, bad curvature region of HSX, where curvature/$\nabla $B scale lengths ($\sim $R/3) and magnetic ripple ($\varepsilon _{H})$ differ from those of a tokamak (R {\&} $\varepsilon _{T}$, respectively). This is justified by GS2 3D [2] calculations, which demonstrate that the dominant linear instabilities (TEM) in HSX are spatially localized in this region. Growth rates from the Weiland model in this limit agree within 30{\%} of growth rates predicted by GS2 for 3D HSX plasmas. Predicted profiles agree with a number of experimental profiles. Predicted confinement times agree within $\sim $20{\%} of experimental confinement times. Confinement times predicted without the local geometry approximation of HSX ($\kappa $/$\nabla $B, $\varepsilon _{H})$ are 2-3$\times $ larger. This work is supported by DOE grant number DE-FG02-93ER54222. [1] H. Nordman et al., Nucl. Fusion \textbf{30}, 983 (1990) [2] E.A. Belli et al., Bull. Am. Phys. Soc. \textbf{46}, No. 8, 232 (2001)