MODELING OF SMALL SCALE RADIO-FREQUENCY INDUCTIVE DISCHARGES FOR ELECTRIC PROPULSION APPLICATIONS

Open Access
Author:
Mistoco, Valerie Fabienne
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 13, 2011
Committee Members:
  • Sven G Bilen, Dissertation Advisor
  • Sven G Bilen, Committee Chair
  • Victor P Pasko, Committee Member
  • Stewart Kendall Kurtz, Committee Member
  • Michael Matthew Micci, Committee Member
  • Kultegin Aydin, Committee Member
Keywords:
  • inductive discharge
  • plasma
  • ion thruster
  • propulsion systems
Abstract:
This work is motivated by the increasing interest in small-scale radio-frequency ion thrusters for micro- and nanosatellite applications, in particular for station- keeping. This specific type of thruster relies on an inductive discharge to produce positive ions that are accelerated by an external electric field in order to produce thrust. Analyzing the particle dynamics within the discharge vessel is critical for determining the performance of these thrusters, particularly as scaling down the size and thrust level of ion thrusters remains a ma jor challenge. Until now the application of this type of propulsion system has been limited to large satellites and space platforms. The approach taken in this work was, first, to perform a simple analysis of the inductive discharge using a transformer model. However, the dimensions of the thruster and the pressure ranges at which it operates called for a different approach than those used in larger thrusters and reactors as the collisional domain and non-locality effects differ significantly. After estimating the non-locality effects by calculating the non-locality parameter, a kinetic description of the discharge was developed. From the input power, mass flow rate, and the properties of the gas used in the discharge, the density numbers, temperatures of the particles, and thrust are calculated. Simulation values are compared with experimental values obtained with the Miniature Radio-frequency Ion Thruster being developed at The Pennsylvania State University. The approach employed to model this small scale inductive discharge can be summarized as follows. First, conditions of operation and the various plasma parameters of the discharge were derived. Then, a one-dimensional kinetic model of an inductive discharge, using a Maxwellian electron distribution, was built. Results from this model were validated on data available in the literature. Finally, from the beam current derived from the 1-D model, using a two-grid ion optic configuration, thrust was calculated. In addition, an existing model of transition between capacitive and inductive modes was applied to the Miniature Radio-frequency Ion Thruster geometry and its electrical properties. A description of the different types of capacitively coupled radio-frequency initiation mechanisms is also given.