Experimental Studies of High-Frequency Oscillations in Hall Thrusters (original) (raw)
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A numerical study of low-frequency discharge oscillations in Hall thrusters
& Proceedings 저널· 프로시딩즈| 기술 …
A 2D numerical model has been constructed for use in modeling Hall thruster plasma dynamics. An important feature is a detailed electron-insulator interaction model which has yielded improved predictions of electron temperature. The complete simulation is used here as a ...
Experimental studies of high-frequency azimuthal waves in Hall thrusters
Physics of Plasmas, 2004
High-frequency oscillations ͑1-100 MHz͒ are drawing significant attention in the recent research of Hall thrusters. A diagnostic setup, consisting of single Langmuir probe, special shielded probe connector-positioner, and electronic impedance-matching circuit, was successfully built and calibrated. Through simultaneous high-frequency probing of the Hall-thruster plasma at multiple locations, high-frequency plasma waves have been successfully identified and characterized.
Discharge Oscillations in a Permanent Magnet Cylindrical Hall-Effect Thruster
Measurements of the discharge current in a cylindrical Hall thruster are presented to quantify plasma oscillations and instabilities without introducing an intrusive probe into the plasma. The time-varying component of the discharge current is measured using a current monitor that possesses a wide frequency bandwidth and the signal is Fourier transformed to yield the frequency spectra present, allowing for the identification of plasma oscillations. The data show that the discharge current oscillations become generally greater in amplitude and complexity as the voltage is increased, and are reduced in severity with increasing flow rate. The 'breathing' mode ionization instability is identified, with frequency as a function of discharge voltage not increasing with discharge voltage as has been observed in some traditional Hall thruster geometries, but instead following a scaling similar to a largeamplitude, nonlinear oscillation mode recently predicted in for annular Hall thrusters. A transition from lower amplitude oscillations to large relative fluctuations in the oscillating discharge current is observed at low flow rates and is suppressed as the mass flow rate is increased. A second set of peaks in the frequency spectra are observed at the highest propellant flow rate tested. Possible mechanisms that might give rise to these peaks include ionization instabilities and interactions between various oscillatory modes.
Suppression of Discharge Current Oscillations in a Hall Thruster
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2005
Results of controlling a discharge current oscillation in Hall thrusters at a frequency range of 10-100 kHz are presented. To understand the discharge current oscillation mechanism, the plasma behavior in the acceleration channel was observed with a high-speed camera using a 1-kW class, anode layer type Hall thruster. The emission intensity oscillates equably in the acceleration channel at the same period of the discharge current oscillation; the number density of excited xenon ions oscillates at the same oscillation period and is proportional to the discharge current. These results indicate that the discharge current oscillation is caused by the ionization instability and the number density of plasma oscillates equably in the acceleration channel. Furthermore, the oscillation amplitude was sensitive to the applied magnetic flux density, indicating that this oscillation is affected by electron mobility. The proposed oscillation model based on the experimental results demonstrated that the momentum transfer corresponding to a plasma fluctuation is crucial to achieving stability. Thus, the oscillation amplitude for various acceleration channel configurations-parallel and convergent-was measured, because channel configuration could affect the momentum transfer. The oscillation was successfully suppressed by adopting the convergent configuration, as shown by this model.
2018
The development and propagation of the electron cyclotron drift instability are experimentally characterized in the acceleration region and near field plume of a 9kW magnetically shielded Hall thruster. High speed measurements of ion saturation current are related to plasma density oscillations in the thruster and analyzed to create spatially resolved dispersion relations. Along channel centerline, and between the exit plane of the thruster and 2.5 cm downstream, spectral power is primarily concentrated at distinct bands in the 3-20 MHz domain, indicative of electron cyclotron resonance peaks. Beyond 2.5 cm a linear ion-acoustic like dispersion is seen up to at least 12 cm downstream. The linear wave is dominant in the E × B direction at frequencies ranging from 70-300 kHz, wavelengths between 12-53 mm, and with a phase speed of 3700 m/s. Spatially resolved power spectra show a correlation between the emergence of the linear wave and changes in wave energy at high frequencies as the...
Characterization of plasma in a Hall thruster operated at high discharge voltage
2005
The electron-wall interaction and its dependence on the discharge voltage and channel width are studied through measurements of the electron temperature, plasma potential and density in a 2 kW Hall thruster. Experimental results are compared with theoretical predictions for different thruster configurations and operating conditions. The channel width is shown to have a more significant effect on the axial distribution of the plasma potential than the discharge voltage.
Numerical and Experimental Investigation of Longitudinal Oscillations in Hall Thrusters
Aerospace
One of the main oscillatory modes found ubiquitously in Hall thrusters is the so-called breathing mode. This is recognized as a relatively low-frequency (10–30 kHz), longitudinal oscillation of the discharge current and plasma parameters. In this paper, we present a synergic experimental and numerical investigation of the breathing mode in a 5 kW-class Hall thruster. To this aim, we propose the use of an informed 1D fully-fluid model to provide augmented data with respect to available experimental measurements. The experimental data consists of two datasets, i.e., the discharge current signal and the local near-plume plasma properties measured at high-frequency with a fast-diving triple Langmuir probe. The model is calibrated on the discharge current signal and its accuracy is assessed by comparing predictions against the available measurements of the near-plume plasma properties. It is shown that the model can be calibrated using the discharge current signal, which is easy to measu...
Spatial evolution of small wavelength fluctuations in a Hall Thruster
Physics of Plasmas, 2019
The spatial evolution of small wavelength (< 1 cm) fluctuations in the Hall direction of a 9-kW class magnetically shielded Hall effect thruster is experimentally characterized. High-speed electrostatic probes are used to measure plasma density perturbations in the acceleration region and near field plume of this cross-field device. Two types of waves are observed: broadband turbulence in the low hundreds of kilohertz and megahertz oscillations characterized by distinct peaks in the measured power spectrum. The lower frequency content is shown to be commensurate with linear ion acoustic-like waves while the higher frequency oscillations are indicative of cyclotron resonances. It is found that the higher frequency content dominates the power spectrum in the upstream acceleration zone and saturates at a fraction (<0.002) of the thermal energy. Downstream of this region, the lower frequency content becomes dominant, growing until the total wave energy again saturates. It is proposed that both the upstream and downstream modes are the same oscillation, the electron drift instability, but in different limits. The transition from upstream to downstream dispersion may be explained by the electron drift instability undergoing an inverse energy cascade as it forms and propagates with the ion drift in the discharge.
Eastern-European Journal of Enterprise Technologies
The object of research reported in this work is the fluctuations of the discharge current in Hall thrusters. The presence of significant fluctuations in the discharge current in Hall thrusters causes a significant deterioration of the thruster parameters – thrust, specific impulse, and efficiency. The task addressed in the current work relates to determining the main factors that affect the conditions for the occurrence of discharge current fluctuations, finding ways to reduce them, and obtaining optimal values of the parameters of the Hall thruster. The review of literary sources revealed that the specified problem is typical and has not yet been solved. In order to solve this problem, studies of the ST-40M Hall thruster were carried out in order to determine the main factors that have the greatest influence on the occurrence of oscillations and means of reducing the oscillations of the discharge current. The result of the research determined that the fluctuations of the discharge ...