Numerical investigations of a cylindrical Hall thruster

K. Matyash, R. Schneider, O. KalentevGreifswald University, Greifswald, D-17487, Germany

Y. Raitses, N. J. FischPrinceton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA

Similar to conventional HTs, the operation involves closed EB 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

2d3v RZ Particle in Cell simulation of 2.6 cm CHT

Electron density profile Potential profile

anomalous electron transport due to Bohm diffusion is included via scattering of electron

perpendicular velocity with 16Bohm

ce

Kv

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 KBohm is too simplistic.

3D model, resolving the azymuthal dynamics is necessary

Length L = f L*

Magnetic field B = f-1 B*

Cross Sections Xs = 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

Simulation geometry

Top viewAxial cross-section

Rectangular Hall thruster is simulated

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

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

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, …)

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

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

Thank you for your attention !