A. Lazurenko

Determination of the electron anomalous mobility through measurements of turbulent magnetic field in Hall thrusters

Measurements of the turbulent magnetic field in a Hall thruster have been carried out between 1kHz and 30MHz with the aim of understanding electron transport through the magnetic field. Small detecting coils at the exit of the accelerating channel and outside of the ionic plume were used to characterize various instabilities. The characteristic frequencies of the observed power spectral densities correspond to known classes of instabilities: low frequency (20–40kHz), transit time (100–500kHz), and high frequency (5–10MHz). A model of the localized electron currents through a magnetic barrier is proposed for the high-frequency instability, and is found to be in good quantitative agreement with the observations. Based on the measured high-frequency turbulent magnetic field, the turbulent electric field is estimated to be about 1V∕cm outside of the plume and ranges from 10to102V∕cm at the channel midradius at the exit of the thruster. The “anomalous” electron collision frequency, related to the high-frequenc...

Experimental investigation of high-frequency drifting perturbations in Hall thrusters

High-frequency instabilities (1–10MHz) in a Hall thruster were studied with the use of six antennas installed in the external ceramic wall of the accelerating channel of the thruster. Azimuthal modes m⩾1 were evidenced in more or less complex shape of the antenna signal, propagating with azimuthal velocity close to the drift velocity in crossed electric and magnetic fields. These instabilities have the highest level at the exit part of the thruster. They were shown to correlate with low-frequency (10–30kHz) oscillations of the discharge current. Information on axial electric field variation is derived from the instabilities properties. The instabilities were characterized as a function of thruster operating parameters—discharge voltage and magnetic field.

Physical characterization of high-frequency instabilities in Hall thrusters

High-frequency instabilities (5–10MHz) were investigated in two Hall thrusters of different scale and were shown to have the same character. Two diagnostic tools were implemented in this study: capacitive antennas, electrically isolated from plasma, and plasma immersed probes. Their corresponding signals were analyzed in terms of capacitive and charge-collecting effects. The previously suggested physical representation of these high frequency instabilities as azimuthally drifting electron density fluctuations was reinforced and significant deviations from azimuthal symmetry in the thruster plume are evidenced. Finally, data obtained by using positively biased probe evidenced lower frequency components, assigned to “ion transit time” instabilities.

Dispersion relation of high-frequency plasma oscillations in Hall thrusters

The dispersion relation of high-frequency plasma oscillations (>1MHz) in a Hall thruster is estimated from two point probe measurements. The probes are located outside the accelerating channel nearby the channel exit. The probe orientation allows us to investigate the evolution of azimuthal and axial wave numbers with the oscillation frequency. The azimuthal dispersion relation is nearly linear. The axial dispersion relation depends upon the probe position, which translates into a varying slope. The observed features of the two dispersion relations can be explained in terms of spatial structure of the high-frequency plasma instabilities.

Experimental Insights Into High-Frequency Instabilities and Related Anomalous Electron Transport in Hall Thrusters

The properties of high-frequency (HF) instabilities (f > MHz) in Hall thrusters are reviewed on the basis of a large experimental data set previously obtained with the use of antennas, probes, and magnetic coils. The phenomenological representations of their physical sources are discussed. The development of these HF instabilities results in anomalous electron transport, and the corresponding transport coefficients are evaluated from these experimental data.

Recent advances in dual-mode Hall effect thruster development

Two SNECMAs Hall-effect thrusters - the 1.5 kW class PPS/sup /spl reg//-1350G and the 5 kW class PPS/sup /spl reg//-X000ML were tested in a wide range of operation parameters. For instance, with a propellant mass-flow rate of 2.3 mg/s for the former and 5 mg/s for the latter, the discharge voltage was ramped up to 1000V. They demonstrated the flexibility in changing of operation parameters and promising performances from the point of view of the dual-mode operation. Particularities about the ion acceleration in the PPS/sup /spl reg//-X000ML are also presented and discussed in this contribution.

Laser injection of ultra-short electron bursts for the diagnosis of Hall thruster plasma

The present developments of Hall thrusters for satellite control and space mission technologies represent a new step towards their routine use in place of conventional thermal thrusters. In spite of their long R and D history, the complex physics of the E ? B discharge at work in these structures has prevented, up to now, the availability of predictive simulations. The electron transport in the accelerating layers of these thrusters is one of the remaining challenges in this direction. From the experimental point of view, any diagnostics of electron transport and electric field in this critical layer would be welcome for comparison with code predictions. Appropriate diagnostics are difficult, due to the very aggressive local plasma conditions. This paper presents the first step in the development of a new tool for characterization of the plasma electric field in the very near exhaust thruster plume and comparison with simulation code predictions.The main idea is to use very short bursts of electrons, probing local electron dynamics in this critical plume area. Such bursts can be obtained through photoelectric emission induced by a UV pulsed laser beam on a convenient target. A specific study, devoted to the characterization of the electron burst emission, is presented in the first section of the paper; the implementation and testing of the injection of electrons in the critical layer of Hall thruster plasma is described in the second section. The design and testing of a fast and sensitive system for characterizing the transport of injected bursts will be the next step of this program. It requires a preliminary evaluation of electron trajectories which was achieved by using simulation code. Simulation data are presented in the last section of the paper, with the full diagnostic design to be tested in the near future, when runs will be available in the renewed PIVOINE facility. The same electron burst injection could also be a valuable input in the present discussion on the physics of the 5?10?MHz instability observed in almost all Hall thrusters.

High-frequency instabilities and low-frequency dynamics in Hall thruster plasma

Investigation of the transients of two time scales was carried out in the SPT-100ML Hall thruster. Detailed experimental studies of the high-frequency instabilities (1-10MHz) were carried out with six antennas installed at various longitudinal and azimuthal positions into the external ceramic wall of the accelerating channel. A complex structure of the signal was observed, varying from the periodic one with clearly defined peaks and a period representing the time of single turn of the electrons rotating at the drift velocity in the crossed electric and magnetic fields, to the structure with much shorter correlation times. Correlation between these instabilities and low-frequency (10-30 kHz) transients in thruster current was studied. Features of HF signals have been investigated for different operation modes of the thruster: discharge voltage Ud=200-450V, anode mass flow rate

Search for the Frequency Content of Hall Effect Thruster HF Electrostatic Wave with the Hilbert-Huang Method

Hall Effect Thruster (HET) plasma oscillations are studied. A set of antennas and an electric probe is used to pick‐up the signals. All the detectors are located in the thruster channel exit plane, at its outer circumference, close to the zone of maximum magnetic barrier of SPT100‐ML device. Each non‐stationary signal is expanded into a finite set of intrinsic modes with the use of Empirical Mode Decomposition (EMD) method. Characteristic bands of instantaneous frequency and power are filtered out by means of Hilbert transform. The analysis is applied to signals recorded in different operating conditions of the HET. The HF oscillations in the frequency range of ∼ 1 ÷ 20 MHz are identified as an electrostatic drift wave propagating along the thruster azimuth. In this band the decrease of discharge voltage results in less defined and broadened frequency spectrum when compared to nominal operating conditions.