Microturbulence has been implicated in anomalous transport at the exit of the Hall thruster, and recent simulations have shown the presence of an azimuthal wave which is believed to contribute to the electron axial mobility. In this paper, the 3D dispersion relation of this E Â B electron drift instability is numerically solved. The mode is found to resemble an ion acoustic mode for low values of the magnetic field, as long as a non-vanishing component of the wave vector along the magnetic field is considered, and as long as the drift velocity is small compared to the electron thermal velocity. In these conditions, an analytical model of the dispersion relation for the instability is obtained and is shown to adequately describe the mode obtained numerically. This model is then fitted on the experimental dispersion relation obtained from the plasma of a Hall thruster by the collective light scattering diagnostic. The observed frequency-wave vector dependences are found to be similar to the dispersion relation of linear theory, and the fit provides a non-invasive measurement of the electron temperature and density. V C 2013 AIP Publishing LLC.

The transition scenario from stability to drift wave turbulence is experimentally investigated in a magnetized low-b plasma with cylindrical geometry. It is demonstrated that the temporal dynamics is determined by the interaction and destabilization of spatiotemporal patterns, in particular, traveling waves. The analysis of the temporal and the spatiotemporal data shows that the bifurcations sequence towards weakly developed turbulence follows the Ruelle-Takens scenario. [S0031-9007(97)04530-4] PACS numbers: 52.35. Kt, 05.45. + b, 52.35.Ra It is an essential feature of bounded plasmas to establish edge localized gradients in the density, the space charge potential, and the particle temperatures. The magnetized plasma is then subjected to a class of low-frequency electrostatic fluid drift instabilities, the collisional drift waves. The dynamics of collisional drift waves is based on the tight coupling of fluctuations caused by E 3 B and diamagnetic drifts perpendicular to the magnetic field and a resistive parallel electron response. Linear drift waves travel predominantly in the transverse direction with electron diamagnetic drift velocity, have a radial eigenmode structure, and tend to establish axially standing modes. Despite important recent progress in theory [1] and experiment [2], the nature of the drift wave turbulence is still far from being understood. In particular, little is known of the strongly nonlinear regime in between the linear instability onset and the fully developed turbulence. In this paper, we describe an experimental study of the transition from a stable state to weakly developed drift wave turbulence in a bounded cylindrical low-b plasma. When the control parameter is increased, the transition follows a well-defined scenario, analogously to the already classical observations in neutral fluids [3]. Of high general interest in spatially extended, dissipative systems is the relationship between the temporal dynamics and spatiotemporal patterns [4], for instance, traveling waves, and we thus devote special attention to this important subject.The drift wave experiment was performed in a triple plasma device with a magnetized central chamber [5]. In one chamber a thermionic argon discharge is operated as plasma source (gas pressure P 8 3 10 24 mbar). The weakly ionized plasma diffuses into the central section and forms a magnetized column (magnetic field B 70 mT) of length l 1.6 m with a Gaussian radial density profile n͑r͒ n 0 exp͑2r 2 ͞2r 2 0 ͒ of width r 0 2.0 cm. The plasma column is bounded on both ends by transparent grids separating it from the source chambers. In the center of the column the electron temperature is T e 1.2 eV and the electron density is n e 2 3 10 16 m 23 . From laser diagnostics in thermionic discharges an ion temperature close to gas temperature was inferred [6], i.e., T e ͞T i ഠ 40. The drift wave characteristic length scales are set by the reduced gyroradius r s 1.0 cm and the inverse density gradient length L 21 n d͑ln n͒͞dr 1͞r 0.5 cm 21 [7]. The time scale is ...

Experiments on spatiotemporal open-loop synchronization of drift wave turbulence in a magnetized cylindrical plasma are reported. The synchronization effect is modeled by a rotating current profile with prescribed mode structure. Numerical simulations of an extended Hasegawa-Wakatani model show good agreement with experimental results.

Both ion and electron temperatures in the scrape-off layer (SOL) of the Tore Supra tokamak were measured by a retarding field analyzer during an ohmic density scan. SOL T i was found to be higher than T e by a factor of 4-7. The ion-to-electron temperature ratio τ decreases with increasing density. Core T i and T e measurements in Tore Supra combined with a multi-machine database of τ measurements show that τ > 1 also in the edge of the confined plasma and increases with radius.