A Preliminary Basic Experiment on the Production and Identification of ETG Modes

The Electron Temperature Gradient (ETG) mode is believed to be a possible candidate for anomalous electron energy transport. The high frequency (few MHz) and short wave length $(k_\perp \rho_e <1)$ make the direct observation of ETG modes difficult in experiments. We have fairly succeeded in producing the parameter regime appropriate for ETG modes in the Columbia Linear Machine (CLM). The requisite electron temperature gradient is obtained via dc acceleration (via a biased screen) and subsequent thermalization in the core of the plasma. The resulting electron temperature of $\sim 20 eV$ in the center and $\sim 1 eV$ in the edge are obtained. This allows us to vary $\eta_e = d ln T_e / d ln N$ from 1 to 6. Fluctuations at $\sim 2 MHz$ correlated with high $\eta_e$ are seen. Much wider and deeper parametric study of these fluctuations is necessary for its identification as ETG modes.