Examination of Faraday probe measurements and plasma conditions supporting detachment

Magnetic nozzles are used in electric propulsion to expand magnetized plasmas to convert the thermal energy to directed kinetic energy, producing thrust. Plasma detachment from magnetic nozzles is a concern since the on-board coils create magnetic fields with closed field lines. A promising scenario for detachment involves expanding the plasma from low beta (sub-Alfvenic flow) to high beta (super-Alfvenic flow) inside the nozzle such that the outgoing plasma stretches the magnetic field lines.; A Faraday probe was designed to take ion current density measurements. With density and magnetic field measurements from other diagnostics, velocity and beta could be determined at axial positions in the plume. A simple model to calculate axial properties using Faraday probe measurements was also developed. When combined with test data, there is strong evidence that transition from sub-Alfvenic (beta < 1) to super-Alfvenic (beta > 1) velocity occurs inside the nozzle, the basic criteria for detachment.