Electron magnetohydrodynamic turbulence in a high-beta plasma. I. Plasma parameters and instability conditions

The interaction of a dense discharge plasma with a weak external magnetic f ield has been studied experimentally. The electron pressure exceeds the fie ld pressure and forms a magnetic hole in the plasma interior. The ions are unmagnetized, while the electrons are in a transition regime from none to f ull magnetization. The electron confinement changes from Boltzmann equilibr ium to magnetic confinement. The pressure balance equation does not describ e the diamagnetism because ambipolar ExB drifts oppose the diamagnetic drif t. The net drift exceeds the sound speed by an order of magnitude and produ ces a strong two-stream cross-field instability. Although its spectrum is c lose to the lower hybrid instability, there are significant differences fro m the classical lower hybrid instability, e.g., the presence of strong magn etic fluctuations. These fall into the regime of electron magnetohydrodynam ics (EMHD) with unmagnetized but mobile ions. While the EMHD turbulence is the main focus of the two following companion papers, this first paper desc ribes the plasma diamagnetism and basic parameters that lead to the instabi lity. (C) 2000 American Institute of Physics. [S1070-664X(00)03111-6].