Finite $\beta$ Effects on TEM Turbulence

This work explores the $\beta$ dependence of trapped electron mode turbulence and associated electron thermal energy and particle transport, using the GS2 (continuum), GEM (particle), and GYRO (continuum) codes. Leadership class computing facilities enable us to extend to shorter wavelengths that contribute significantly to electron thermal transport, which can increase with $\beta$ in ITG dominated cases.\footnote{J. Candy, Phys. Plasmas {\bf 12}, 072307 (2005). See posters by R. Waltz and W. Nevins, this conference.} Analytic work on zonal flow modulational instabilities with finite $\beta$ suggests interesting and non-monotonic $\beta$ dependence, arising from competition between drift wave and drift-Alfv\'{e}n wave pumps.\footnote {P. N. Guzdar {\em et al.}, Phys. Plasmas 8(9) 3907 (2001).} Finally, our previous TEM zonal flow studies\footnote{D. R. Ernst, J. Lang, W. M. Nevins {\em et al.}, Phys. Plasmas 16, 055906 (2009).} found that convergence was poor for $\eta_e> 3$, despite including wavenumbers $k_\alpha\rho_s\le 4$. Additional physics, such as electromagnetic effects, could potentially resolve this.