Observation of Electromagnetic Drift-Alfvén Waves in Increased $\beta$ Laboratory Plasmas (PhD Oral-24)

The variation of pressure-gradient driven turbulence with plasma $\beta$ (up to $\beta \approx 15\%$) is investigated in linear, magnetized plasma. The magnitude of magnetic fluctuations is observed to increase substantially with increasing $\beta$. More importantly, parallel magnetic fluctuations are observed to dominate at higher $\beta$ values, with $\delta B_\parallel / \delta B_\perp \approx 2$ and $\delta B / B \approx 1\%$. Parallel magnetic fluctuations are strongly correlated with density fluctuations and the two are observed to be out of phase. The relative magnitude of and cross-phase between density and parallel magnetic field fluctuations are consistent with dynamic pressure balance ($P+\frac{B_{\parallel}^2}{2\mu_0} = $ constant). A local theory of modified drift-Alfvén waves, including parallel magnetic fluctuations is qualitatively and quantitatively consistent with the observations.