Experimenal Characterization of a Carbon Nanotube Field Emission Cathode

There is interest in the use of carbon nanotubes (CNTs) to create a field emission cathode. The primary benefit of this cathode is that a gas flow is not required to create electrons, which is of critical importance for space missions that must minimize propellant mass. A field emission cathode consisting of CNT arrays is fabricated by the Georgia Tech Research Institute and the Georgia Tech High-Power Electric Propulsion Laboratory. The cathode is tested at pressures below 3 x 10 -5 Torr. The average output current density is measured over a cathode voltage range of 250-800 V relative to the gate for several CNT cathodes. The highest stable emission current density is 0. 6 mA/cm 2 . The emission current density is measured throughout a 50-hour life test at a cathode voltage of 550 V which demonstrated an overall constant emission current density of 0.51 mA/cm 2 with an emission current to input power ratio of 1.7 mA/W.