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Numerical investigations of a cylindrical Hall thruster K. Matyash, R. Schneider, O. Kalentev Greifswald University, Greifswald, D-17487, Germany Y. Raitses, N. J. Fisch Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA

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Similar to conventional HTs, the operation involves closed E B electron drift. Fundamentally different from conventional HTs in the way the electrons are confined and the ion space charge is neutralized: Electrons are confined in the hybrid magneto- electrostatic trap Ions are accelerated in a large volume-to- surface area channel (potentially lower erosion) Raitses and Fisch, Phys. Plasmas 8, 2579 (2001) Cylindrical Hall Thruster

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2d3v RZ Particle in Cell simulation of 2.6 cm CHT Electron density profilePotential profile anomalous electron transport due to Bohm diffusion is included via scattering of electron perpendicular velocity with K. Matyash, R. Schneider, O. Kalentev, Y. Raitses, N. J. Fisch, Annual meeting of APS-DPP, Nov. 2010 Although the simulated plasma parameters were in overall agreement with the experiment, the simulation did not reproduce the changes due to enhanced cathode emission: the model for anomalous electron transport with constant K Bohm is too simplistic. 3D model, resolving the azymuthal dynamics is necessary

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LengthL = f L * Magnetic fieldB = f -1 B * Cross SectionsXs = f -1 Xs * Geometry scaling e - + Xe → Xe + + 2e - ionization e - + Xe → Xe * + e - total excitation e - + Xe → Xe + e - elastic scattering Xe + + Xe → Xe + + Xe elastic scattering Xe + Xe + → Xe + + Xe charge exchange e -, Xe + Coulomb collisions All relevant collisions are included Scaling factor f = 0.1 is used in the present simulations Monte-Carlo secondary electron emission (SEE) model at the dielectric surface In the present simulations no SEE at the dielectric walls was accounted ( = 0 ) Neutral dynamics self-consistently resolved with direct simulation Monte Carlo (DSMC) Kinetic treatment of all plasma species 3 dimensional Particle in Cell code with Monte-Carlo collisions Cartesian geometry and the regular mesh (X,Y,Z) guarantees conservation of momentum and absence of self forces in the PIC algorithm 60x60x80 grid is used

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Simulation geometry Top view Axial cross-section Rectangular Hall thruster is simulated

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The plasma cloud in the annular part is rotating in direction of ExB drift with v ~ 1.8 km/s Strong oscillations of the azimuthal E-field and the azymuthal depletion of neutrals are associated with its rotation

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Rotating spoke in the CHT experiments Leland Ellison, Yevgeny Raitses and Nathaniel J. Fisch, IEPC-2011-173 The spoke rotating at 15-35 kHz, corresponding to a speed of 1.2 – 2.8 km/s in direction of ExB drift was observed experimentally in CHT

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Dependence of the spoke position on the cathode placement In the simulation the spoke position is defined by the cathode placement The further investigations are necessary to study dependence on other asymmetry sources (neutral gas injection, magnetic field, …)

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Oscillations of azimuthal E-field with E ~ 100 V/cm, f ~ 10 MHz and ~ 5 mm are responsible for the electron transport toward the anode in the simulations Such oscillations were not observed experimentally in CHT, possibly due to frequency bandwidth limitations Plasma dynamics inside the spoke

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Conclusions Full 3D PIC MCC model for CHT is developed The model is able to resolve the anomalous electron transport due to azimuthal E-field oscillations The spoke rotating with v ~ 1.8 km/s is observed in the simulations Spoke rotation is associated with azimuthal depletion of the neutral gas and strong azimuthal E-field oscillations with E ~ 100 V/cm and f ~ 10 MHz Further joint simulation and experiment efforts are necessary for clarification of the phenomena underlying the spoke formation and the dynamics as well as electron transport inside the spoke Funding by DLR is kindly acknowledged

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Thank you for your attention !

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