Computer modeling and comparison with diagnostic results of a downscaled High Efficiency Multi Stage Plasma Thruster

Transcription

1 Chart 1 Computer modeling and comparison with diagnostic results of a downscaled High Efficiency Multi Stage Plasma Thruster T. Brandt 1,3+, Th. Trottenberg 3, R. Groll 2, F. Jansen 1, Fr. Hey 4, U. Johann 4, H. Kersten 3, C. Braxmaier 1,2-1 DLR Institut für Raumfahrtsysteme Bremen - 2 ZARM Bremen - 3 Christian Albrechts Universität Kiel - 4 Airbus D & S, Friedrichshafen

2 Chart 2 Overview - Introduction - Simulation setup - Results - Outlook - Summary

3 Chart 3 Introduction - µn thruster: Need for Space Missions Demand - Future formation flying missions (LISA respectively NGO e.g., NGGM e.g.) need µn propulsion Specific requirement Thrust: µN Noise <0.1µN/ Hz LISA Image: Airbus Defence and Space

4 Chart 4 Introduction - Idea: Scaling Thales HEMP-Thruster down in µn domain feasible? thrust approx 100 mn specific impulse ~3000 s erosion free operation minimal complexity

5 Chart 5 Introduction - micro HEMP-T development and measurement campaign o Promising results, 10 µn region reached. o Possibly design changes necessary to reach 1 µn region. o Improved understanding of plasma behavior in discharge chamber required. o Computer modeling of discharge chamber and near plume region. Prototype 3

6 Chart 6 Model setup: Particle in cell (PIC) overview o Direct tracing of particles F = e(e + v B) Example: o Usually thousands of particles summed up to super particles o Large distance interactions (magnitude of Debye length) solved on a grid o Close distance interactions (e.g. Coulomb collisions) solved by Monte Carlo code grid super particle

7 Chart 7 Model setup: geometry / elements Model 1 Model 2 grounded potential anode potential (400 V) ceramic (surface charge accumulation) magnets magnetic field lines electron source

8 Chart 8 Model setup: two models common neutral gas inflow: 0,55 SCCM anode voltage: 400 V electron source current adjusted to get to the measured 7 ma anode current differences Model 1 Larger outside domain Electrons near exit region Not all electrons go through full potential step Time resolution allows for max electron speed of 2E6 m/s => 12 ev Model 2 Smaller outside domain Electrons at outer rim of outside domain =>all electrons go through full potential step Time resolution allows for max. electron speed of 8E6 m/s => 182 ev

9 Chart 9 Model setup : real and virtual measurement of angular depended ion beam current Simulation model 1, model 2: Virtual measurement-points Thruster: Real measurement-points (with Faraday cups) Measurement by Andreas Keller

10 Chart 10 Results: electric potential V grounded potential anode potential (400 V) ceramic surface Model 1 Model 2 Mostly flat potential in discharge chamber (not really multi-stage) Diagonal shaped potential drop at the exit.

11 Chart 11 Results: Xenon ion movement V_z Model 1 V_r Model 2

12 Chart 12 Results: angular depended ion beam current measurement Simulation model 1 Simulation model 2 85 µn 9 µn 80 µn

13 Chart 13 Outlook: to do list Combine best of both models: large exit region and high time resolution Replace static background neutral gas with moving neutral particles Additional effects, secondary electron emission, double charged Xenon ions, etc..

14 Chart 14 Summary Flat potential inside the thrusters discharge channel For model with large outside domain (model 1): Ion beam shows hollow cone - typical for HEMP- Thrusters Model 1: Ion beam angular distribution in good agreement with experimental results, but overall simulated ion beam flow to low, hence simulated thrust to low. Model 2: Simulated ion beam flow and thrust in good agreement with experimental results, but Ion beam angular distribution not. Several factors found for improvement of simulation to bring it to better agreement with experiment

15 Chart 15 THANKS FOR YOUR ATTENTION