The influence of neutral flow rate in the operation of Hall thrusters.

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Overview

Neutral flow dynamics in Hall thrusters are not often regarded as a critical aspect that controls thruster operation and discharge channel physics. This dissertation, combined with previous work, showed that neutral flow dynamics affect global properties including thruster performance, stability, thermal margin, and lifetime. In addition, the neutral flow rate, and more importantly, the electron-neutral collision rate in the channel have an impact on other thruster properties including the location, size, and intensity of the ionization, high electron temperature, and acceleration regions. The results of these findings are relevant to ongoing efforts to understand thruster operation, electron physics, and thruster lifetime.;Performance and plume measurements indicated that thruster efficiency remained constant from +/- 50% of the nominal flow rate of 20 mg/s. Current utilization was the primary loss mechanism and it decreased with flow rate due to increased ionization losses and electron-wall losses. To compensate, the divergence and mass utilizations increased with flow rate through a more compact ionization region and increased ionization efficiency from the increasing neutral density.;Electron collision frequencies and the electron Hall parameter were calculated from measurements of the ion density, electron temperature, and electric field inside the discharge channel. The peak Hall parameter moved downstream and decreased in magnitude as flow rate was increased, and the results confirmed that there exist at least three distinct electron mobility regions as implemented in some plasma simulations. Near the anode, the turbulence was approximated by the Bohm value. Near the channel exit, the turbulence was suppressed and electrons were most effectively trapped by the Hall current in this region. In the plume, the turbulence was an order of magnitude greater than the Bohm value, indicating large contributions to electron transport from turbulence or a currently unaccounted for anomalous transport mechanism. For most of the channel, the electron-neutral collisions were the primary contributor to electron energy loss and cross-field mobility. However, near the channel exit, electron-wall collisions increased and became the primary contributor to the measured decrease in electron temperature with increased flow rate.
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Product Details

  • ISBN-13: 9781109113273
  • Publisher: ProQuest LLC
  • Sold by: Barnes & Noble
  • Format: eTextbook
  • Pages: 348
  • File size: 5 MB

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