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Gaussian e-beam pattern generators should use the highest obtainable brightness of the electron source to improve the throughput for a given definition 1. Therefore in these machines it is desirable to use sharp-tip cathodes. When LaB6 is the cathode material the optimization of the relevant parameters is very difficult due to the non-homogeneous emission pattern 2 . Usually direct observation of the source is not possible in these production machines. The only means which give an insight into the electron-optic column are emission current, beam current, spot characteristics and settings of alignment coils and lenses. Moreover, when only one alignment unit is used with several lenses, several local optima can exist in the alignment. As a result, the optimum of these non-orthogonal parameters is difficult to obtain, even for a skilled operator. Mang pattern generators avoid these difficulties by using a flat-tipped cathode, but at the penalty of lower brightness. Therefore, software has been developed to achieve the optimum setting automatically using the knowledge of the dynamic behaviour of the different parameters to limit the multi-dimensional space in which these parameters have to be optimised. This limitation is necessary because a search through all possible settings would require an unacceptable amount of machine time. For a full understanding of the algorithms an explanation of the physical processes is necessary. Also the effect of handling by the operator and the change of parameters with time must be included. The software adjusts the cathode temperature, according to the specified brightness (while never overheating the tip), selects the correct part of the beam and sets the required spotsize. The optimization time is dominated b physics and electronics and not b the algorithms. The adjustment time of the tip temperature is determined mainly b the heat capacitance of the complete cathode assembly mounting; the time to find the correct lobe and alignment is determined by the time constant of the alignment coils and drivers and the spotsize setting by the time constants of lenses and drivers. A short overview will be given about the conditions for use of LaB6 as a cathode material to obtain high brightness and long life, particularly the vacuum specifications (P< 2.10E-8 torr) and filament temperature (T< 1800 K).
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