Non-Maxwellian Electron Energy Probability Functions in the plume of a SPT-100 Hall thruster

We present measurements of the electron density, the effective electron temperature, the plasma potential, and the electron energy probability function (EEPF) in the plume of a 1.5 kW-class SPT-100 Hall thruster, derived from cylindrical Langmuir probe measurements. The measurements were taken on the plume axis at distances between 550 and 1550 mm from the thruster exit plane, and at different angles from the plume axis at 550 mm for three operating points of the thruster, characterized by different discharge voltages and mass flow rates. The bulk of the electron population can be approximated as a Maxwellian distribution, but the measured distributions were seen to decline faster at higher energy. The measured EEPFs were best modelled with a general EEPF with an exponent alfa between 1.2 and 1.5, and their axial and angular characteristics were studied for the different operating points of the thruster. As a result, the exponent alfa from the fitted distribution was seen to be almost constant as a function of the axial distance along the plume, as well as across the angles. However, the exponent alfa was seen to be affected by the mass flow rate, suggesting a possible relationship with the collision rate, especially close to the thruster exit. The ratio of the specific heats, the gamma factor, between the measured plasma parameters was found to be lower than the adiabatic value of 5/3 for each of the thruster settings, indicating the existence of non-trivial kinetic heat fluxes in the near collisionless plume. These results are intended to be used as input and/or testing properties for plume expansion models in further work.This work was performed in the framework of the 'Model and Experimental validation of spacecraft-thruster Interactions (erosion) for electric propulsion thrusters plumes' (MODEX) project. MODEX is a collaboration between Airbus-DS, ESA, UC3M, ONERA, CNRS-ICARE and KTH aiming to provide a better understanding of the plasma properties in the far-plume of a Hall thruster. The project aimed at providing experimental measurements to better constrain the modelling, and therefore includes both the theoretical/modelling aspect (UC3M and ONERA) and the experimental aspect (KTH, CNRS, ESA and Airbus-DS). The test campaign was conducted at ESA/ESTEC in April-May 2017, using a SPT-100 Hall thruster provided by Airbus-DS. G Giono and J T Gudmundsson were partially supported by the Swedish Government Agency for Innovation Systems (VINNOVA) contracts no. 2016-04094 and 2014-0478, respectively

Characterisation of the analogue read-out chain for the CCDs onboard the mesospheric airglow/aerosol tomography and spectroscopy (MATS)

The MATS satellite aims at observing airglow and noctilucent clouds in the mesosphere. The main instrument consists of a six channels limb imager in the near-ultraviolet and near-infrared. A high signal-to-noise ratio is required for detecting these mesospheric phenomena: 100 and 500 for ultraviolet and infrared, respectively. This is achieved by an optical design minimizing stray-light, but also with a dedicated design of the read-out analogue chain for the CCD on each channel. The requirements and expected light level on the imaging channels are brie y discussed before focusing on the CCD read-out analogue chain, for which the design and performances are presented

Non-Maxwellian electron energy probability functions in the plume of a SPT-100 Hall thruster

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