| The study of enhanced field emission from broad area niobium cathodes, and the characterization of individual sites are presented. This experiment was built [1] in a UHV surface analysis system which included a SEM, a scanning Auger microscopy facility and also an in situ heat treatment unit where the samples could be annealed up to 2000°C. Upon heat treatment of the niobium samples, it is observed that the density of field emitting sites increases with the heat treatment temperature up to 900°C whereafter the density decreases sharply. After heat treatments at 1400°C and higher we have been able to obtain, consistently, emission free surfaces at 100 MV/m. Further heat treatments of the emission free sample show a maxima in the density of field emitting sites at 800°C. These sites were either activated or created during the heat treatment. Typical examples of the activated and created sites are presented. |
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