In the BLAAMA" device a wealdy ionized hydrogen plasma is produced by electrons accelerated from a hoL negatively biosed tungsten filament and confined in a toroidal magnetic field of strength up to 0.4 T. The plasma is turbulent, with relative fluctuation levels in ne, # and Tc of 10% or more. The time-averaged state exhibits nested toroidal surfaces of constant potential and pressure, which requires an anomalous cross-field cumeat to remove the spacecharge injected by the cathode and the charge accumulated due to the VB-and C U N ~U E drifts. Typical plusma parameters me n, -10l6 m-3, T, .. 1-20 eV, Z -I eV. The cross-field diffusion coefficient is typically DI -30 m2 s-' -IO4 x Of"""' -10' x DY". Evidence is presented in support of the hypothesis that the placma goes turbulent beuuse it needs to develop an anomalous current channel. nnd this turbulence in tum determines the plasma transport and the time-averaged state.
An experimental study of low-frequency electrostatic fluctuations is presented for a plasma produced by a steady-state discharge in a magnetized toroidal plasma device without a rotational transform. A significant intermittency of the fluctuations is observed. Thus the evolution and propagation of large coherent vortical structures is demonstrated by a conditional sampling technique. The flutelike nature of the structures is explicitly demonstrated. The analysis includes measurements of fluctuations in plasma density, electric potential, and electron temperature. The relevance of the observations to anomalous transport in the device is pointed out. The performance of the conditional sampling technique is compared to a simple correlation analysis by a Monte Carlo simulation.
An experimental study of low frequency electrostatic fluctuations is presented for a plasma produced by a steady state discharge in a toroidal device. The evolution and propagation of large coherent vortical structures is demonstrated by a conditional sampling technique.The brutelike nature of the structures is explicitly demonstrated.PACS numbers: 52.35. Ra, 52.25.Fi, 52.25.Gj A toroidally magnetized, collisionless plasma without a rotational transform does not possess a nontrivial ideal MHD equilibrium [1]. A quasi-steady-state plasma distribution can nevertheless be produced by maintaining a discharge to balance losses of plasma and electric charge. A thorough description and discussion of this type of discharge was given in [1]. It was observed that the plasma state was strongly influenced by the charge injected via the filament cathode. Estimates show that classical transport (in our case dominated by ion-neutral collisions) is not sufficient to provide the cross-field current necessary to compensate the charge injected into the toroidal magnetic fIux tube intersecting the filament.It was also shown that classical transport is insufficient to compensate the charge accumulation due to guiding center drift of electron and ions (VB and curvature drift), although the latter accumulation is small compared to that arising from electron injection. Hence, for nontrivial, inhomogeneous plasma states the radial cross-field current is anomalous in nature. The radial pressure force on the plasma is balanced by the j~X B force which arises from the poloidal diamagnetic current jg, and the radial anomalous current component is balanced by a poloidal anomalous viscous force V T, where T = p vv is the Reynolds turbulent stress tensor arising from the inclusion of ion inertia in the momentum equation [1].Here p is the fluid mass density and v is the Quid velocity. These ideas were recently formulated into a complete single fIuid model for the turbulent state of the axisymmetric torus by Rypdal [2]. Numerical simulations based on this model will be presented in forthcoming papers. Reference [2] also presented a generalization of the proof for nonexistence of an MHD equilibrium given in [3]. Their nonexistence theorem was generalized to a turbulent equilibrium and to include plasma source terms. It was shown that, even though turbulence could provide sufficient cross-field current to provide charge balance, a plasma source term would be necessary to maintain such a turbulent equilibrium.An interesting aspect of these developments is that some degree of magnetic confinement is shown to be possible even in the absence of an MHD equilibrium. Although the confinement may be insufficient for fusion applications, we believe that many naturally occurring plasmas belong to this class, and an increasing number of laboratory devices are designed for the study of such plasmas.In this Letter we describe experimental studies in the Blaamann device at the University of Tromsp, Norway, emphasizing the role of large scale electrostatic vor...
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