Accession Number:

ADA482721

Title:

Advanced Cathodes for Next Generation Electric Propulsion Technology

Descriptive Note:

Master's thesis, Mar 2007-Mar 2008

Corporate Author:

AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT

Personal Author(s):

Report Date:

2008-03-01

Pagination or Media Count:

174.0

Abstract:

The research presented here investigated the feasibility of a 6.4 mm Lanthanum Hexaboride LaB6 and Cerium Hexaboride CeB6 hollow cathode for low power electric propulsion applications 100-300W. Two orifice geometries, one anode configuration, several anode and keeper currents, and a range of flow rates were tested for the LaB6 cathode. The CeB6 cathode underwent the same tests, with the exception of the second orifice geometry due to time constraints. The required instruments include an oscilloscope to monitor the keeper and anode voltages, a Langmuir probe measured electron temperature, plasma densities, and plasma potential for the coupling plasma, infrared imaging studied the thermal characteristics of each cathode, electron microscopy for surface contaminant analysis, and high-speed imaging for coupling plasma observations. The oscilloscope, Langmuir probe, and high-speed camera determined the cathodes mode of operation and gave information that indicated stable spot mode or unstable, destructive plume mode. The CeB6 cathode operated in spot mode as low as 1.5 A and 1.5 sccm with no heater or keeper power, and as high as 6 A, 1.5 sccm with 1 A keeper current. Increasing the flow rate and keeper current mitigated plume mode. The CeB6 cathode was more susceptible to poisoning than the LaB6 cathode, requiring more heater power and flow to start after running at low flow and current for long periods. The CeB6 cathode also operated at slightly higher temperatures than the LaB6 cathode, indicating a higher emissivity. The LaB6 cathode ran in spot mode as low as 2.5 A, at 1.5 sccm with no heater or keeper power. However, when the aspect ratio was reduced to 0.25, the cathode operated as low as 1.4 A, with 1.5 sccm until the cathode exceeded the voltage limit of the power supply. The same spotplume mode characteristics were observed for LaB6 as CeB6.

Subject Categories:

  • Electrical and Electronic Equipment
  • Electric and Ion Propulsion

Distribution Statement:

APPROVED FOR PUBLIC RELEASE