Electromagnetic turbulence in increased β plasmas in the Large Plasma Device

The variation of pressure-gradient-driven turbulence with plasma $β$ (up to $β ≈ 15 %$) is investigated in linear, magnetized plasma. The magnitude of magnetic fluctuations is observed to increase substantially with increasing $β$. More importantly, parallel magnetic fluctuations are observed to dominate at higher $β$ values, with $δ B_\parallel / δ B_\perp ≈ 2$ and $δ B / B_0 ≈ 1 %$. 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 the dynamic pressure balance ($P+{B₀^2}/{2μ _0} = \textrm {constant}$). A local slab model theory for electromagnetic, modified drift Alfvén waves, including parallel magnetic fluctuations, shows partial agreement with experimental observations.