J. Kurzyna

Spectral analysis of Hall-effect thruster plasma oscillations based on the empirical mode decomposition

Hall-effect thruster plasma oscillations recorded by means of probes located at the channel exit are analyzed using the empirical mode decomposition (EMD) method. This self-adaptive technique permits to decompose a nonstationary signal into a set of intrinsic modes, and acts as a very efficient filter allowing to separate contributions of different underlying physical mechanisms. Applying the Hilbert transform to the whole set of modes allows to identify peculiar events and to assign them a range of instantaneous frequency and power. In addition to 25kHz breathing-type oscillations which are unambiguously identified, the EMD approach confirms the existence of oscillations with instantaneous frequencies in the range of 100–500kHz typical for ion transit-time oscillations. Modeling of high-frequency modes (ν∼10MHz) resulting from EMD of measured wave forms supports the idea that high-frequency plasma oscillations originate from electron-density perturbations propagating azimuthally with the electron drift v...

Closed-loop control of ionization oscillations in Hall accelerators

Feedback control of ionization oscillations in Hall accelerators is investigated with a proportional-integral-derivative controller acting on the discharge voltage. The stability of the current is found to systematically improve with proportional control, whereas integral and derivative control have in most cases a detrimental or insignificant impact. At low discharge voltages, proportional control eliminates at the same time ionization breathing oscillations as well as a coexisting low frequency mode. A progressive deterioration of the stability is observed at higher voltage, presumably attributable to the limited output voltage range of the controller. The time-averaged characteristics of the discharge such as average current, thrust and efficiency, remain unchanged within measurement uncertainties.

Plasma inside a small Hall thruster for satellites

The plasma properties inside the channel of a small Hall effect thruster (petit propulseur innovant) equipped with permanent magnets are analysed by the fluid numerical code HETMAn. The local variables of electron density, electron and ion currents, and parallel and perpendicular electron temperatures are calculated as functions of time. The time-dependent and averaged values of the thruster performance (thrust: 13 mN, specific impulse: 1328 s) are obtained. The global efficiency is 34%.

Chaotic waves in Hall thruster plasma

The set of hyperbolic equations of the fluid model describing the acceleration of plasma in a Hall thruster is analyzed. The characteristic feature of the flow is the existence of a trapped characteristic”; i.e. there exists a characteristic line, which never intersects the boundary of the flow region in the thruster. To study the propagation of short wave perturbations, the approach of geometrical optics (like WKB) can be applied. This can be done in a linear as well as in a nonlinear version. The nonlinear version describes the waves of small but finite amplitude. As a result of such an approach one obtains so called transport equation, which are governing the wave amplitude. Due to the existence of trapped characteristics this transport equation appears to have chaotic (turbulent) solutions in both, linear and nonlinear versions.

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.

High Frequency Oscillations In 2‐D Fluid Model Of Hall Effect Thrusters

2‐D linearised plasma dynamics equations for Hall Thruster plasmas are examined with special attention focused on the effect of spatial non‐uniformity of the unperturbed state. Introducing fast and slow (separated) scales of plasma parameter variation, the stability conditions for HF modes are discussed.