Comparison of SPT and HEMP thruster concepts from kinetic simulations

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1 Comparison of SPT and HEMP thruster concepts from kinetic simulations K. Matyash, R. Schneider, A. Mutzke, O. Kalentev Max-Planck-Institut für Plasmaphysik, EURATOM Association, Greifswald, D-1749, Germany F. Taccogna Istituto di Metodologie Inorganiche e dei Plasmi-CNR, Via Amendola 122/D, Bari, Italy N. Koch, M. Schirra THALES Electron Devices GmbH, D Ulm, Germany

2 Particle in Cell simulation of HEMP DM3a thruster Schematic view of HEMP thruster concept HEMP thruster DM3a has been developed and tested in an early stage of HEMP thruster development in 2002 and has demonstrated the feasibility of this new thruster concept

3 Particle in Cell simulation of HEMP DM3a thruster Electrostatic Particle in Cell code with Monte-Carlo collisions t 2 dimensional in space (RZ) 3 dimensional in velocity (2d3v)

4 Particle in Cell simulation of HEMP DM3a thruster Scaling laws used in the model Collisions included in the model Length Magnetic field Neutral density Current Plasma Density Electric potential L = f L * B = f -1 B * n G =f -1 n * G I = f 2 I * n p = n * p V = V * e - + Xe Xe + + 2e - e - + Xe Xe * + e - e - + Xe Xe + e - Xe + + Xe Xe + + Xe Xe + Xe + Xe + + Xe ionization total excitation elastic scattering elastic scattering charge exchange Temperature Electric field T = T * E = E * f = 0.1 is applied in the simulation Energy is not scaled atomic physics is preserved Debye length remains unchanged reduction of the computational grid cell number

5 Particle in Cell simulation of HEMP DM3a thruster Computational domain with potential profile L max = 89 mm R max = 24 mm Uniform grid 890x240 Extended domain with the nearfield region Ions accelerated at the exit

6 Particle in Cell simulation of HEMP DM3a thruster Electron density profile Xe + density profile Plasma contacts the wall only in magnetic cusps positions Ion space charge in exit remains uncompensated no need for neutralizer

7 Particle in Cell simulation of SPT100 ML z y j B x

8 Particle in Cell simulation of SPT100 ML Computational domain with magnetic field L thruster = 25 mm R INthruster = 34.5 mm R OUTthruster = 50 mm U Anode = 300 V B max = 180 Gauss Magnetic field used as reference L max = 80 mm R max = 80 mm Magnetic field was calculated with Finite Element Magnetic Field Solver (FEMM) L. Garrigues et. al., Phys. Plasmas, 10 (2003) 4886

9 Particle in Cell simulation of SPT100 ML Radial magnetic field along the system (at r = mm) Simulation L. Garrigues et. al., Phys. Plasmas, 10 (2003) 4886

10 Particle in Cell simulation of SPT100 ML Potential profile Ions accelerated along the whole channel

11 Particle in Cell simulation of SPT100 ML Electron density profile Xe + density profile Quasi-neutrality holds also after exit neutralization of ion beam necessary

12 Particle in Cell simulation of SPT100 ML Electron temperature profile E z /B r ratio along the median line in the SPT100 ML channel The efficiency of the electron heating rate is proportional to the energy electrons gain from the electric field on the Larmour radius ~E z /B r

13 Particle in Cell simulation of SPT100 ML Electron-impact ionization rate profile Ionization region close to the anode

14 PIC MCC simulation of HEMP DM3a and SPT100 ML Ion fluxes to the channel wall Mean energy of the ions Ion flux non-negligible in HEMP only at cusp position Corresponding energy below the sputtering threshold

15 Erosion simulation with SDTrimSP code SDTrimSP Monte-Carlo binary collision approximation code Erosion rates for Xe + on BN for various incidence angles Very good match of physical sputtering Dynamical changes of surface composition Erosion threshold ~ V Pronounced angle dependence

16 Erosion simulation with SDTrimSP code Erosion rate calculated with SDTrimSP code for SPT100 ML and HEMP DM3a The energy-, angle-, axial positionresolved ion fluxes calculated with PIC MCC code are used as input data for SDTrimSP simulations. No erosion in the dielectric channel of HEMP thruster

17 Particle-in-Cell simulations of plasma thrusters Suitable for different types (SPT, HEMP) Inclusion of near-field region of plume Coupling to binary collision model for plasma-surface interaction Next steps: Self-consistent neutral dynamics Further extension of domain (plume) Full 3D (anomalous electron transport) Acknowledgments German Space Agency DLR Project No. 50 RS R.S. : Initiative and Networking Fund of the Helmholtz Association.