Experimental Investigation of Turbulence and Transport in the Helimak Configuration

Density fluctuations and transport in the Helimak device are investigated as a function of the connection length, $L_c$, and gas species. Radial equilibrium profiles for Ar and He show structure where $n$ and $T_e$ peak outside the electron cyclotron resonance radius. Due to the fact that the magnetic field on the LFS has unfavorable curvature, density fluctuation levels on this side are increased. For short $L_c$ results are consistent with the idea that these fluctuations are unstable drift waves. As $L_c$ increases, the LFS gradient becomes steeper and the fluctuation levels increase to more than $50\%$. Probability distribution functions in this region display highly non-Gaussian structure, and raw data suggests plasma here exhibits intermittency. In He plasmas a quasi-periodic oscillation occurs at longer $L_c$ which appears to consist of two or more low frequency components, $f_k<1$ kHz. Both radial and parallel transport are investigated with results indicating that at longer $L_c$ the particle fluxes are dominated by transport perpendicular to the magnetic field. Work supported by US Department of Energy grant DE-FG03-00ER54609