Fusion Turbulence without a Toroidal Magnetic Field

Three decades since Surko and Slusher\footnote{Surko and Slusher, {\it Science} {\bf 221}, 817 (1983).}, fusion scientists have achieved tremendous progress understanding driven turbulence and turbulent transport in tokamaks. Nonlinear gyrokinetic theory provides a workable formalism for simulating gradient-driven turbulent transport, and recent validation studies in high-power reactor-relevant regimes show important areas of agreement. The new application of nonlinear gryokinetic theory to toroidal magnetic confinement without a toroidal magnetic field is an important opportunity to extend the reach of turbulence models used for magnetic fusion to different geometries, to higher beta plasmas ($\beta \sim 1$), and to plasma confined in magnetospheres. Magnetic geometry strongly influences turbulent mixing, and low-frequency fluctuations are enturely field-aligned for a toroidal plasma confinement by a purely poloidal field. Fusion turbulence without a toroidal field eliminates coupling between parallel streaming and perpendicular decorrelation, drives either a particle pinch or a thermal pinch\footnote{Kesner, {\it et al., Phys Plasmas} {\bf 18}, 050703 (2011).}, and exhibits 2D dynamics and the inverse energy cascade\footnote{Grierson, {\it et al., Phys Plasma} 16, 55892 (2009)}