Ion Current in Hall Thrusters


In order to match observed thrust and discharge current in Hall thrusters, computer simulations have typically assumed anomalous electron transport mechanisms, such as Bohm diffusion, to enhance electron mobility across magnetic field lines. Without enhanced electron transport, the simulations predict much lower discharge current than observed, and too much of the potential drop is downstream of the channel exit. Rather than search for mechanisms to increase the electron scattering frequency, we seek to identify mechanisms that would increase the fraction of the current carried by ions, thus reducing the required electron current. We describe two mechanisms that enhance the current carried by ions. The first increases the ion current carried in the channel by simply including the effects of doubly-charged ions on the plasma response. The importance of using accurate ionization cross sections and the need to include doubly-charged ions even for 300 V discharge voltages is discussed. The second is a process we term “ion reflux.” In this process, current is carried by ions generated downstream of the channel exit. A portion of these ions impact the center insulator and are neutralized by cathode electrons. A large fraction of the resultant neutral atoms are re-ionized as they pass through the main exhaust beam and these newly born ions then carry additional current through the plume. Both of these mechanisms tend to reduce the need to invoke anomalous electron transport mechanisms. These are just two specific mechanisms that enable ions to carry more of the cross-field current. There may be more mechanisms revealed as this general concept is further pursued.

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@inproceedings{Katz2007IonCI, title={Ion Current in Hall Thrusters}, author={Ira Katz and Richard Hofer and D . M . Goebel}, year={2007} }