High-current Cold Cathode Field Emission Array for Electron Lens Application

During Phase I, the following goals were achieved: (1) design and fabrication of a novel, nano-dimensional CNT field emitter assembly for high current density application, with high durability; (2) fabrication of a ceramic based micro channel plate (MCP) and characterization of its secondary electron emission; and (3) characterizing the CNT/MCP cathode for high field emission and durability. As a result of these achievements, a relatively high current density of ~ 1.2 A/cm 2 from a CNT cathode and single channel MCP were measured. The emission current was also extremely stable with a peak-to-peak variation of only 1.8%. The emission current could be further enhanced to meet requirements for electron lens applications by increasing the number of MCP channels. A calculation for maximum possible current density with a 1200 channel/cm 2 MCP, placed over a cathode with 1200 uniformly functioning CNTs, would be ~1.46 kA/cm 2 , neglecting space charge limitations. Clearly this level of emission is far greater than what is needed for the electron lens application, but it does offer a highly comforting margin to account for sub-standard emitters and/or to allow the lesser challenge of building a cathode with fewer channels/cm 2 . A satisfactory goal for the electron lens application would be a controllable emission of 2-4 mA per channel in an ensemble of 8001200 uniformly-functioning channels/cm 2 , and a cathode with overall area of about 1 cm 2 .