Mulvey has described microscope lenses which are considerably smaller than conventional lenses due to the higher current densities which he can achieve by using a more efficient cooling system. There are some difficulties associated with this type of lens, however, which make it potentially difficult to use in high resolution microscopes. First of all, the velocity of water flow is necessarily high in order to provide the cooling required (0.5 Watts/cm2) , making the Reynolds number high and turbulence inevitable. Such turbulence produces vibration. Secondly, the temperature rise is high so that one cannot easily avoid increasing the temperature of the column which can lead to outgassing and subsequent specimen contamination.
High temperature machine: Characterization of materials for the electrical insulation