An experimental analysis of magnetic fluctuations is performed in the plasma produced by a modified MPD thruster, equipped with passive systems for the control of magneto-hydrodynamic (MHD)instabilities, and in particular of the virulent kink instability. The development of the helical kink mode, due to a violation of the Kruskal-Shafranov criterion, is indeed known to be responsible for the increased power losses and the unstable operating behaviour, associated to the so called ‘onset’ phenomenon observed in this kind of devices when a critical current level is exceeded. The thruster was operated both in self-field and in applied-field configurations, with a maximum axial magnetic field of 100 mT induced by an external coil on the axis of the thruster. The effect of the passive control system on plasma instability is analysed in terms of the levels of the magnetic field fluctuations and of their axial, azimuthal and time periodicities, the diagnostic set up consisting of a system of magnetic coils located in the interelectrode and in the external plume regions. Different geometries of the control system have been tested and the effectiveness of each of them in reducing plasma instabilities at different plasma current levels are analysed.
Magnetic Fluctuations in an MPD Thruster with Passive Systems for the Control of MHD Instabilities
PAGANUCCI, FABRIZIO;ANDRENUCCI, MARIANO;
2007-01-01
Abstract
An experimental analysis of magnetic fluctuations is performed in the plasma produced by a modified MPD thruster, equipped with passive systems for the control of magneto-hydrodynamic (MHD)instabilities, and in particular of the virulent kink instability. The development of the helical kink mode, due to a violation of the Kruskal-Shafranov criterion, is indeed known to be responsible for the increased power losses and the unstable operating behaviour, associated to the so called ‘onset’ phenomenon observed in this kind of devices when a critical current level is exceeded. The thruster was operated both in self-field and in applied-field configurations, with a maximum axial magnetic field of 100 mT induced by an external coil on the axis of the thruster. The effect of the passive control system on plasma instability is analysed in terms of the levels of the magnetic field fluctuations and of their axial, azimuthal and time periodicities, the diagnostic set up consisting of a system of magnetic coils located in the interelectrode and in the external plume regions. Different geometries of the control system have been tested and the effectiveness of each of them in reducing plasma instabilities at different plasma current levels are analysed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
