Turning plasma technology into an engineering discipline, it is necessary to understand, model and control the design and performance of plasma thrusters for space application there is a need for plasma measurement of the downstream plasma plume.
One of the most useful plasma diagnostics is the Langmuir probe. First developed in GE laboratories as a tool to understand plasma lighting application it is now a standard product used for the measurement of key plasma parameters.
It is necessary to measure the plasma parameters to know if your understanding of the behaviour of the plasma is repeatable and under control. There is little point in investing significant funds in a development project to develop a plasma thruster if the results are not repeatable. To engineer a robust solution you need a model of the process and that model needs to be tested to confirm the expected results.
The following paper is a good example of the use of a Langmuir to investigate the downstream decay of the plasma plume of thruster.
IEPC-2017-357
Presented at the 35th International Electric Propulsion Conference
Georgia Institute of Technology • Atlanta, Georgia USA October 8 – 12, 2017
Abstract:
it is desirable to develop and have access to plasma models usable in day-to-day industrial processes which are able to reproduce with sufficient accuracy the electric
field build-up and potential decay downstream the thruster and around the satellite, to
effectively predict the ions trajectory towards the surfaces. An experimental validation of those models is mandatory to gain confidence in the ir adequacy. In this context, the MODEX study, funded by the European Space Agency (ESA) and involving a consortium led by Airbus Defense and Space, aims at: i) identifying the key physical processes governing electron cooling and electric field build-up downstream the thruster in the far field, ii) proposing models of electron cooling that are physically representative and simple enough to be implemented in the SPIS software, iii) experimentally validating on-ground at ESTEC-EPL those models using a typical EP thruster used on telecom platforms, and tuning the model to the data, iv) performing system applications including erosion analyses, using both the data obtained and the models implemented, and compare the two approaches. The first 3 phases have been done so far and are described in this paper.
Mike B Hopkins 