Design and Implementation of an Actuated Probe Suite for an Orificed Hollow Cathode

Abstract

A system of diagnostics consisting of a reciprocating triple probe was developed to measure the axial variation of the plasma density within an orificed hollow cathode. The system was created to validate a charge-exchange-limited diffusion model. Finite element models were created to ensure that the thermal and mechanical loads of steady-state cathode operation do not destroy or deform the structure. The reciprocating probe is actuated by a vacuum-rated stepper motor. A visual interface and controller was programmed in Labview to fully automate the system and track the position of the probe. The system was fabricated using computer-aided manufacturing techniques, and assessed during cathode operation. During operation, the position of the probe can traverse the active zone of the cathode in 2.5 seconds. Its position was tracked at a maximum rate of 30 queries per second. The system was tested under a vacuum of 10−5 torr, where a plasma was generated in the cathode. Steady-state operation was not achieved, and probe measurements were unable to be performed. The system experienced no deformation from the cathode initialization, indicating that the system is capable of withstanding the thermal and mechanical loads of steady-state operation. The diagnostics will be used for further experimentation within the Electric Propulsion and Plasma Dynamics Laboratory of Princeton University.