Cylindrical Langmuir probe measurements in a Helium plasma were performed and analysed in the presence of a magnetic field. The plasma is generated in the ALINE device, a cylindrical vessel 1 m long and 30 cm in diameter using a direct coupled RF antenna (ν RF = 25 MHz). The density and temperature are of the order of 10 16 m −3 and 1.5 eV, respectively, for 1.2 Pa Helium pressure and 200 W RF power. The axial magnetic field can be set from 0 up to 0.1 T, and the plasma diagnostic is a RF compensated Langmuir probe, which can be tilted with respect to the magnetic field lines. In the presence of a magnetic field, I(V) characteristics look like asymmetrical double probe ones (tanh-shape), which is due to the trapping of charged particles inside a flux tube connected to the probe on one side and to the wall on the other side. At low tilting angle, high magnetic field amplitude, power magnitude and low He pressure, which are the parameters scanned in our study, a bump can appear on the I(V) in the plasma potential range. We then compare different models for deducing plasma parameters from such unusual bumped curves. Finally, using a fluid model, the bump rising on the characteristics can be explained, assuming a density depletion in the flux tube, and emphasizing the role of the perpendicular transport of ions.

中文翻译：

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圆柱形朗缪尔探针在磁化氦等离子体中获得的碰撞特性的实验和理论研究

在存在磁场的情况下执行和分析氦等离子体中的圆柱形朗缪尔探针测量。等离子体是在 ALINE 装置中产生的，这是一个长 1 m、直径 30 cm 的圆柱形容器，使用直接耦合射频天线 (v RF = 25 MHz)。对于 1.2 Pa 氦气压力和 200 W RF 功率，密度和温度分别约为 10 16 m -3 和 1.5 eV。轴向磁场可以设置为 0 到 0.1 T，等离子体诊断是一个射频补偿朗缪尔探头，它可以相对于磁场线倾斜。在存在磁场的情况下，I(V) 特性看起来像不对称的双探针（tanh 形状），这是由于带电粒子被困在连接到一侧探针和连接壁的通量管内另一边。在低倾角时，高磁场幅度、功率大小和低 He 压力是我们研究中扫描的参数，在等离子体电位范围内的 I(V) 上可能会出现凸起。然后，我们比较了从这种不寻常的凹凸曲线推导出等离子体参数的不同模型。最后，使用流体模型，可以解释特性上的凸块上升，假设通量管中的密度耗尽，并强调离子垂直传输的作用。