Using emittance measurements system for diagnostic of ion thruster
Aerospace propulsion engineering
Аuthors1, 2*, 3, 2**, 1, 1
1. Justus-Liebig Universitaet Giessen, Institut fuer Atom- und Molekuelphysik, Heinrich-Buff-Ring 16, Giessen, 35392, Germany
2. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
3. Southampton University , S017 1BJ, United Kingdom
Tracing of the ion trajectories would give a large amount of information about the ion thruster. The genuine method is introduced that an interrelation of the results of a full simulation of the ion trajectories with the results of an experiment, measuring the emittance of the source would give an access to the plasma parameters of the discharge in the ion thruster. Furthermore measuring the emittance in different distances would give valuable information about the thrust vector and its variation and also beam forming itself with prospective evaluation of the space charge. Usage of emittance measurements for optimization of basic aperture for extraction system can give reliable indication its perfection in terms of divergence and correspondingly lifetime.
The emittance of the beam is the 6D-volume which beam occupies in phase space of coordinates and impulses. For the computer modelling is the KOBRA3-INP code used. KOBRA is a Vlasov-solver. It starts with the solution of the Poisson equation. A space charge map is built during the ray-tracing. This particle distribution map is included in the following iteration step to obtain the self-consistent particle distribution.
The method is developed for measurements on a Mini Radio Frequency Ion Thruster (RIT) but can be used for any ion thruster technology. These type of thrusters are candidate for many future science and Earth Observation missions based on formation flying and fine attitude control. Although this method is well known for the high energetic ions like the ion beam injectors for the TOKAMAK heating, the method is new for such low energy ions.
Measurement of the emittance is performed using the slit-wire-method. The primary ion beam is separated into a bunch of beamlets by passing an array of slits. Behind this slit array in an appropriate distance the spatial distribution of the beamlets is scanned with a thin wire. The position of the wire is quantified with a precise potentiometer. To obtain the four-dimensional transversal beam emittance the primary beam can be splitted by two perpendicular slit arrays. To reduce distortion of the profile measurement by secondary particles, a repeller voltage can be applied on the slit system. With this method each data point is characterized by its position, divergence angle and intensity. Experimental results and comparisons with computer modeling will be presented.
Keywords:emittance, ion thruster, ion-optic system, ion beam
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