MEASURED TEMPERATURE DROPS ALONG FIELD EMITTERS

Temperature drops down field electron emitter needles from their supporting (heated) filaments to their submicroscopic hemispherical tips were measured by a new technique. Emitter needles of hafnium, which undergo an allotropic solid phase transformation at a known high temperature, were heated until the alpha to beta transformation which occurred at the tip could be seen through the field electron emission pattern. An optical pyrometer was used to determine the filament temperature. Using published optical pyrometer was used to determine the filament temperature. Using published values of emissivity and thermal conductivity for bulk hafnium, computed results, using classical heat conduction and radiation theory, gave temperature drops that were much too small. Calculated temperature drops for Hf below the transformation temperature and for W needles are presented for comparison.