No abstract

The edge region of the reversed field pinch experiment RFX has been investigated with Langmuir and calorimetric probes. The energy flux measurements reveal a spatial structure that is consistent with the presence of a superthermal tail in the energy distribution function of the electrons, as expected according to the kinetic dynamo theory (KDT). In the framework of this model, the value of the magnetic field line diffusion coefficient in the edge region has been derived. The radial electric field obtained from the plasma potential gradient is opposite in sign to the ambipolar electric field expected in a stochastic magnetic field. The discrepancy is discussed in terms of particle recycling at the wall.

Measurements of magnetic and electrostatic fluctuations in an applied field magneto-plasma-dynamic thruster have shown that a m/n=1/1 kink mode becomes unstable whenever the Kruskal-Shafranov limit is violated. A positive correlation is established between the kink and performance degradation at high current, which has until now prevented the use of this kind of thruster in space missions.

An electrostatic electron energy analyser has been inserted for the first time in the outer region of the RFX reversed-field pinch experiment, in order to investigate and characterize the presence of a superthermal electron population. It has been found that these electrons carry most of the current density parallel to the magnetic field. The time evolution during a single discharge of the superthermal electrons current density and parallel temperature indicates that the distortion of the electron distribution function is stationary during the plasma current flat-top phase. The dependence of the superthermal temperature on the plasma parameters has been investigated by varying the plasma density, and a relationship with the ratio of the on-axis applied electric field to the critical electric field for runaway generation has been identified.