Effect of Conductive Walls on the Performance of a Pulsed Inductive Thruster

The magnetic field produced by the acceleration coil of a pulsed inductive thruster (PIT) interacts not only with the plasma current sheet but also with the conductive walls of the vacuum chamber in which testing is performed. A quantitative evaluation of this interaction and its effects is made through the use of both a magnetostatic model to compute the evolution of the magnetic field topology as the plasma moves and an inductive thruster performance model to calculate thruster performance. The 1-m-diameter PIT MkVa thruster is evaluated as it represents the most successful inductive thruster to date and was tested in a conductive vacuum chamber possessing a radius of 60 cm. As the conductive walls are moved radially inward, closer to the acceleration coil, the magnetic field topology becomes compressed, lowering the overall inductance of the coil and reducing the electromagnetic acceleration imparted to the plasma. The computed performance data indicate that as the chamber radius is increased from 60 cm to infinity, representing in space conditions, the specific impulse and thrust efficiency increase by 4% and 7.5%, respectively. This underscores the importance of testing a PIT in a chamber that is either constructed of a nonconducting material or is significantly larger than the thruster diameter when attempting to accurately measure thruster performance.