In the past, Ion beam diagnostics on FEEP thrusters was performed by means of simple electrostatic wire probes, which yield qualitative information on the ion current density distribution in the beam, integrated over the length of the probe. As these probes are neither suited to local investigation, nor capable of electron temperature and plasma potential measurement, some tests with double Langmuir probes have been recently carried out at Centrospazio. The aim of the activity was to develop a simple but nonetheless effective diagnostic tool for the investigation of phenomena occurring in the plasma plume of a FEEP thruster. To this end, the classical theory of electrost:ltic Langmuir probes was reviewed and adapted to the specific case of a plume with high directed ion velocities. In this modified theory the thruster plume is modelled as a collisionless and quasi-neutral plasma without external magnetic fields; the complex phenomena occurring in the immediate proximity of the probe are simplified and represented through the model of a wake region downstream of the probe. Secondary electron emission from the probe surface due to high-energy impacts of ions is taken into account through a constant current amplification factor. The experlmental part of this work comprised the construction of two double filament Langmuir probes and their integration in an existing FEEP test facility. A subsequent series of tests demonstrated, for the first time, the feasibility of Langmuir probing in a rarefied, high-velocity FEEP ion beam. Data obtained during these tests was analyzed and compared with theoretical previsions. It is shown that this technique is capable of providing conclusive results for two major quantities such as the specific plasma density and the electron temperature.
FEEP Thruster Plume Investigation with Langmuir Probes
MARCUCCIO, SALVO;ANDRENUCCI, MARIANO
1995-01-01
Abstract
In the past, Ion beam diagnostics on FEEP thrusters was performed by means of simple electrostatic wire probes, which yield qualitative information on the ion current density distribution in the beam, integrated over the length of the probe. As these probes are neither suited to local investigation, nor capable of electron temperature and plasma potential measurement, some tests with double Langmuir probes have been recently carried out at Centrospazio. The aim of the activity was to develop a simple but nonetheless effective diagnostic tool for the investigation of phenomena occurring in the plasma plume of a FEEP thruster. To this end, the classical theory of electrost:ltic Langmuir probes was reviewed and adapted to the specific case of a plume with high directed ion velocities. In this modified theory the thruster plume is modelled as a collisionless and quasi-neutral plasma without external magnetic fields; the complex phenomena occurring in the immediate proximity of the probe are simplified and represented through the model of a wake region downstream of the probe. Secondary electron emission from the probe surface due to high-energy impacts of ions is taken into account through a constant current amplification factor. The experlmental part of this work comprised the construction of two double filament Langmuir probes and their integration in an existing FEEP test facility. A subsequent series of tests demonstrated, for the first time, the feasibility of Langmuir probing in a rarefied, high-velocity FEEP ion beam. Data obtained during these tests was analyzed and compared with theoretical previsions. It is shown that this technique is capable of providing conclusive results for two major quantities such as the specific plasma density and the electron temperature.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
