The linear theory for plasma stability in a Hall-type thruster shows that high frequency oscillations are generated inside the thruster. These oscillations generate waves propagating along the channel. The frequencies depend on the value of different discharge parameters and the direction of propagation depends on the studied region. Here, two approaches will be proposed according to the value of the radial magnetic field and the sign of its gradient. An experimental detection performed outside the channel shows agreement between the models and the experiments. These waves appear as being “quasilongitudinal” inside the channel and azimuthal outside the channel.
The design improvements of future plasma thrusters require the investigation of the physical phenomena occurring during the thruster operation. We have investigated a small, Hall-type thruster (or stationary plasma thruster). The different currents and the thrust of the thruster will be reported. Plasma parameters have been measured with Langmuir probes located outside the thruster. Finally, an electrostatic ion energy analyzer located in the plume has permitted the determination of the ion energy distribution function.
The electron energy distribution function measured at the channel exit of a small Hall-type thruster is interpreted as a beam–plasma electron distribution function with electron beam energy of several tens of electronvolts. Though unstable, the distribution function does not correspond to the completely quasilinear relaxed beam function. Comparison with the measured function in the vicinity of the channel exit shows that the electron beam energy is about 30 eV for the total voltage applied ∼200 V. The contribution of the electron beam is shown to be essential in the ionization of the working gas, even when only the single ionization processes are considered.
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